As well-known, the excessive discharge of heavy-metal mercury not only destroys the ecological environment, bust also leads to severe damage of human health after ingestion via drinking and bioaccumulation of food chains, and mercury ion (Hg2+) is designated as one of most prevalent toxic metal ions in drinking water. Thus, the high-performance monitoring of mercury pollution is necessary. Functional nucleic acids have been widely used as recognition probes in biochemical sensing. In this work, a carbazole derivative, ethyl-4-[3,6-bis(1-methyl-4-vinylpyridium iodine)-9H-carbazol −9-yl)] butanoate (EBCB), has been synthesized and found as a target-lighted DNA fluorescent indicator. As a proof-of-concept, Hg2+ detection was carried out based on EBCB and Hg2+-mediated conformation transformation of a designed DNA probe. By comparison with conventional nucleic acid indicators, EBCB held excellent advantages, such as minimal background interference and maximal sensitivity. Outstanding detection capabilities were displayed, especially including simple operation (add-and-read manner), ultrarapidity (30 s), and low detection limit (0.82 nM). Furthermore, based on these advantages, the potential for high-performance screening of mercury antagonists was also demonstrated by the fluorescence change of EBCB. Therefore, we believe that this work is meaningful in pollution monitoring, environment restoration and emergency treatment, and may pave a way to apply EBCB as an ideal signal transducer for development of high-performance sensing strategies.

Accurate determination of intracellular glucose is very important for exploring its chemical and biological functions in metabolism events of living cells. In this paper, we developed a new noninvasive and highly selective nanokit for intracellular glucose monitoring via two-step recognition. The liposome-based nanokit coencapsulated the aptamer-functionalized gold nanoparticles (AuNPs) and the Shinkai’s receptor together. When the proposed nanokit was transfected into living cells, the Shinkai’s receptor could recognize glucose first and then changed its conformation to endow aptamers with binding and sensing properties which were not readily accessible otherwise. Then, the binary complexes formed by the intracellular glucose and the Shinkai’s receptor can in situ displace the complementary oligonucleotide of the aptamer on the surface of AuNPs. The fluorophore-labeled aptamer was away from the AuNPs, and the fluorescent state switched from “off” to “on”. Through the secondary identification of aptamer, the selectivity of the Shinkai’s receptor could be greatly improved while the intracellular glucose level was assessed by fluorescence signal recovery of aptamer. In the follow-up application, the approach exhibits excellent selectivity and is noninvasive for intracellular glucose monitoring under normoxia and hypoxia. To the best of our knowledge, this is the first time that the advantages of organic receptors and nucleic acids have been combined and highly selective monitoring of intracellular glucose has been realized via two-step recognition. We expect it to open up new possibilities to integrate devices for diagnosis of various metabolic diseases and insulin delivery.

•Recent concepts and strategies in ctDNA detection is reviewed.•Targeted approaches with known mutations and untargeted approaches without knowledge of specific changes are described.•Advantages and limitations of different types of strategies are summarized and discussed.•The future trends for clinical application is pointed out.Circulating tumour DNA (ctDNA) isolated from peripheral blood has recently been shown to be a biomarker to detect gene mutations for the diagnosis, treatment, and prognosis of cancer. Utilizing ctDNA as the liquid biopsy has significant potential to pave the way toward a better understanding of cancer at the molecular level and improve patient outcomes in the future. Over the past decades, a large number of efforts have been devoted to the development of valid methods for analysing ctDNA, which provide researchers and clinicians a variety of tools to detect and monitor tumours. In this review, we displayed an overview of current representative technologies for the detection of ctDNA and discuss recent technical advancements. Then, the challenges and outlooks in this promising field are featured on the basis of its current development.

Nitric oxide (NO) is often involved in many different physiological processes including the regulation of lysosomal functions. However, it remains a great challenge to explore the variations of NO levels in lysosomes, limiting the understanding behind its biological functions in cellular signaling pathways and various diseases. Herein, a pH-activatable fluorescent probe, Rhod-H-NO, was designed and synthesized for the determination of lysosomal NO, in which the activation response model is beneficial towards getting accurate biological information. To ensure that Rhod-H-NO can accumulate effectively and exist stably in lysosomes without interference and degradation from other active species, Rhod-H-NO was engineered into the nanopores of mesoporous silica nanoparticles (MSNs) with β-cyclodextrin (β-CD) as the gatekeeper to obtain a nanolab. The nanolab was successfully applied to detect lysosomal NO in living cells and in vivo with high time and spatial resolution. This nanolab could serve as an excellent molecular tool to exploit and elucidate the function of NO at sub-cellular levels.

A ratiometric two-photon fluorescent probe for SO2 derivatives was first proposed based on acedan–merocyanine dyads via a TP-FRET strategy. It was successfully applied to visualization of the fluctuations of enzymatically generated SO2 derivatives in the mitochondria of HepG2 cells and rat liver tissues using two-photon fluorescence microscopy imaging.

By virtue of its high sensitivity and rapidity, Fenton reaction has been demonstrated as a powerful tool for in vitro biochemical analysis; however, in vivo applications of Fenton reaction still remain to be exploited. Herein, we report, for the first time, the design, formation and testing of Fenton reaction for in vivo fluorescence imaging of hydrogen peroxide (H2O2). To realize in vivo fluorescence imaging of H2O2 via Fenton reaction, a functional nanosphere, Fc@MSN-FDNA/PTAD, is fabricated from mesoporous silica nanoparticle (MSN), a Fenton reagent of ferrocene (Fc), ROX-labeled DNA (FDNA), and a cationic perylene derivative (PTAD). The ferrocene molecules are locked in the pore entrances of MSN, and exterior of MSN is covalently immobilized with FDNA. As a key part, PTAD acts as not only the gatekeeper of MSN but also the efficient quencher of ROX. H2O2 can permeate into the nanosphere and react with ferrocene to product hydroxyl radical (·OH) via Fenton reaction, which cleaves FDNA to detach ROX from PTAD, thus in turn, lights the ROX fluorescence. Under physiological condition, H2O2 can be determined from 5.0 nM to 1.0 μM with a detection limit of 2.4 nM. Because of the rapid kinetics of Fenton reaction and high specificity for H2O2, the proposed method meets the requirement for real applications. The feasibility of Fc@MSN-FDNA/PTAD for in vivo applications is demonstrated for fluorescence imaging of exogenous and endogenous H2O2 in cells and mice. We expect that this work will not only contribute to the H2O2-releated studies but also open up a new way to exploit in vivo Fenton reaction for biochemical research.

The levels of circulating tumor DNA (ctDNA) in the peripheral blood have been associated with tumor burden and malignant progression. However, ultrasensitive detection of ctDNA in blood remains to be explored. Herein, we have developed a new approach, employing DNA-mediated surface-enhanced Raman scattering (SERS) of single-walled carbon nanotubes (SWNTs), that allows ultrasensitive detection of a broad range of ctDNAs in human blood. Combined with the efficient ctDNA recognition capacity of our designed triple-helix molecular switch and RNase HII enzyme-assisted amplification, the T-rich DNA-mediated SERS enhancement of SWNTs could read out a content of KRAS G12DM as low as 0.3 fM, with a detection of 5.0 μL of sample volume, which has potential for point-of-care testing in clinical analysis.

G-quadruplex analogues have been widely used as molecular tools for detection of potassium ion (K+). However, interference from a higher concentration of sodium ion (Na+), enzymatic degradation of the oligonucleotide, and background absorption and fluorescence of blood samples have all limited the use of G-quadruplex for direct detection of K+ in blood samples. Here, we reported, for the first time, an intermolecular G-quadruplex-based assay capable of direct fluorescent detection of blood K+. Increased stringency of intermolecular G-quadruplex formation based on our screened G-rich oligonucleotide (5′-TGAGGGA GGGG-3′) provided the necessary selectivity for K+ against Na+ at physiological ion level. To increase long-term stability of oligonucleotide in blood, the screened oligonucleotide was modified with an inverted thymine nucleotide whose 3′-terminus was connected to the 3′-terminus of the upstream nucleotide, acting as a blocking group to greatly improve antinuclease stability. Lastly, to avoid interference from background absorption and autofluorescence of blood, a G-quadruplex-binding, two-photon-excited ligand, EBMVC-B, was synthesized and chosen as the fluorescence reporter. Thus, based on selective K+ ion-induced formation of intermolecular G-quadruplex and EBMVC-B binding, this approach could linearly respond to K+ from 0.5 to 10 mM, which matches quite well with the physiologically relevant concentration of blood K+. Moreover, the system was highly selective for K+ against other metal ions, including Na+, Ca2+, Mg2+, Zn2+ common in blood. The practical application was demonstrated by direct detection of K+ from real blood samples by two-photon fluorescence technology. To the best of our knowledge, this is the first attempt to exploit molecular G-quadruplex-based fluorescent sensing for direct assay of blood target. As such, we expect that it will promote the design and practical application of similar DNA-based sensors in complex real systems.

Visual biopsy has attracted special interest by surgeons due to its simplicity and practicality; however, the limited sensitivity of the technology makes it difficult to achieve an early diagnosis. To circumvent this problem, herein, we report a visual signal amplification strategy for establishing a marker-recognizable biopsy that enables early cancer diagnosis. In our proposed approach, hydrogen peroxide (H2O2) was selected as a potential underlying marker for its compact relationship in cancer progression. For selective recognition of H2O2 in the process of visual biopsy, a benzylbenzeneboronic acid pinacol ester-decorated copolymer, namely, PMPC–Bpe, was synthesized, affording the final formation of the H2O2-responsive micelles in which amylose was trapped. The presence of H2O2 activates the boronate ester recognition site and induces it releasing abundant indicator amylose, leading to signal amplification. The indicator came across the solution of KI/I2 added to the sample, and the formative amylose–KI/I2 complex has a distinct blue color at 574 nm for visual amplification detection. The feasibility of the proposed method is demonstrated by visualizing the H2O2 content of cancer at different stages and three kinds of actual cancerous samples. As far as we know, this is the first paradigm to rationally design a signaling amplification-based molecular recognizable biopsy for visual and sensitive disease identification, which will extend new possibilities for marker-recognition and signal amplification-based biopsy in disease progressing.

It is well-known that cyanide ion (CN–) is a hypertoxic anion, which can cause adverse effects in both the environment and living beings; thus, it is highly desirable to develop strategies for detecting CN–, especially in water and food. However, due to the short half-life of free cyanide, long analysis time and/or interference from other competitive ions are general challenges for accurate monitoring of CN–. In this work, through the investigation on the sequence-dependent optical interaction of DNA-CuNPs with the fluorophore (e.g., EBMVC-B), we found, for the first time, that DNA-CuNPs were an ideal alternative as fluorescence quencher in constructing a sensor which could be illuminated by CN– based on an Elsner-like reaction and that the signal switching was dependent on poly(AT/TA) dsDNA sequence. By virtue of CuNPs’ small size and its high chemical reactivity with cyanide, the lighting of fluorescence was ultrarapid and similar to the hairtrigger “turn-on” of a lamp, which is significant for accurately monitoring a target of short half-life (e.g., cyanide). Attributed to the unique Elsner-like reaction between CN– and the Cu atoms, high selectivity was achieved for CN– monitoring by the nanolamp, with practical applications in real water and food samples. In addition, because of the highly efficient in situ formation of DNA-CuNPs and the approximative stoichiometry between CN– and Cu2+ in the fluorescence switching, the nanolamp could be reversibly turned on and off through the alternate regulation of CN– and Cu2+, displaying potential for developing reusable nanosensors and constructing optical molecular logic circuits.

The development of nanoprobes suitable for two-photon microscopy techniques is highly desirable for mapping biological species in living systems. However, at the current stage, the nanoprobes are restricted to single-color fluorescence changes, making it unsuitable for quantitative detection. To circumvent this problem, we report here a rational design of a dual-emission and two-photon (TP) graphene quantum dot (GQD420) probe for imaging of hydrogen peroxide (H2O2). For specific recognition of H2O2 and lighting the fluorescence of TPGQD420, a boronate ester-functionalized merocyanine (BMC) fluorophore was used as both target-activated trigger and the dual-emission fluorescence modulator. Upon two-photon excitation at 740 nm, TPGQD420–BMC displays a green-to-blue resolved emission band in response to H2O2 with an emission shift of 110 nm, and the H2O2 can be determined from 0.2 to 40 μM with a detection limit of 0.05 μM. Moreover, the fluorescence response of the TPGQD420–BMC toward H2O2 is rapid and extremely specific. The feasibility of the proposed method is demonstrated by two-photon ratiometrically mapping the production of endogenous H2O2 in living cells as well as in deep tissues of murine mode at 0–600 μm. To the best of our knowledge, this is the first paradigm to rationally design a dual-emission and two-photon nanoprobe via fluorescence modulation of GQDs with switchable molecules, which will extend new possibility to design powerful molecular tools for in vivo bioimaging applications.

•Endogenous redox group in spiropyran skeleton avoids the appearance of the false positive signals.•SWCNTs effectively amplify the electrochemical signal to improve the detection sensitivity.•The specific reaction between F− and silica shows excellent anti-interference ability in urine and blood samples.In the past decades, numerous electrochemical sensors based on exogenous electroactive substance have been reported. Due to non-specific interaction between the redox mediator and the target, the instability caused by false signal may not be avoided. To address this issue, in this paper, a new electrochemical sensor based on spiropyran skeleton, namely SPOSi, was designed for specific electrochemical response to fluoride ions (F−). The breakage of Si–O induced by F− based on the specific nucleophilic substitution reaction between F− and silica would directly produce a hydroquinone structure for electrochemical signal generation. To improve the sensitivity, SPOSi probe was assembled on the single-walled carbon nanotubes (SWCNTs) modified glassy carbon electrode (GCE) through the π–π conjugating interaction. This electrode was successfully applied to monitor F− with a detection limit of 8.3 × 10−8 M. Compared with the conventional F− ion selected electrode (ISE) which utilized noncovalent interaction, this method displays higher stability and a comparable sensitivity in the urine samples.

Amyloid-β (Aβ) peptide as one of the main components of senile plaques is closely related to the onset and progression of incurable Alzheimer's disease (AD). Numerous efforts have been devoted to develop probes for Aβ species/plaque imaging for AD diagnostics and to develop aggregation inhibitors preventing formation of toxic soluble oligomeric Aβ for therapeutics. Herein, for the first time, a series of novel charged molecules, which can simultaneously perform near infra-red in vivo imaging of Aβ species/plaques in animal model and inhibition of self-aggregation of Aβ monomer from forming toxic oligomers, are reported. Among them, DBA-SLOH showed excellent blood-brain barrier (BBB) permeability and biocompatibility due to the incorporation of lipophilic alkyl chains with moderate length into the charged skeleton. Importantly, DBA-SLOH was found to have a high binding affinity toward Aβ species exhibiting a dramatic fluorescence enhancement upon interacting with Aβ species. Despite a weaker binding with Aβ monomers as compared to Aβ aggregates, DBA-SLOH could effectively prevent the Aβ1-40 and Aβ1-42 peptides from self-aggregation and forming toxic oligomers. This multifunctional fluorescent molecule shows promising potential as a theranostic agent for the diagnosis and therapy of AD.

•This work developed a quadratic SERS signal amplified method for telomerase activity detection.•This method is PCR-free and enzyme-free.•The limit of detection was calculated to be as low as single cell.•It is capable of distinguishing cancer cell from a vast majority of normal cells.•This method allowed the sensing of telomerase activity from cancer tissues.As an important biomarker and therapeutic target, telomerase has attracted extensive attention concerning its detection and monitoring. Recently, enzyme-assisted amplification approaches have provided useful platforms for the telomerase activity detection, however, further improvement in sensitivity is still hindered by the single-step signal amplification. Herein, we develop a quadratic signal amplification strategy for ultrasensitive surface-enhanced Raman scattering (SERS) detection of telomerase activity. The central idea of our design is using telomerase-induced silver nanoparticles (AgNPs) assembly and silver ions (Ag+)-mediated cascade amplification. In our approach, each telomerase-aided DNA sequence extension could trigger the formation of a long double-stranded DNA (dsDNA), making numerous AgNPs assembling along with this long strand through specific Ag–S bond, to form a primary amplification element. For secondary amplification, each conjugated AgNP was dissolved into Ag+, which can effectively induce the 4-aminobenzenethiol (4-ABT) modified gold nanoparticles (AuNPs@4-ABT) to undergo aggregation to form numerous “hot-spots”. Through quadratic amplifications, a limit of detection down to single HeLa cell was achieved. More importantly, this method demonstrated good performance when applied to tissues from colon cancer patients, which exhibits great potential in the practical application of telomerase-based cancer diagnosis in early stages. To demonstrate the potential in screening the telomerase inhibitors and telomerase-targeted drugs, the proposed design is successfully employed to measure the inhibition of telomerase activity by 3’-azido-3’-deoxythymidine.

Hypoxia is considered to contribute to pathophysiology in various cells and tissues, and a clear understanding about the relationship between hypoxia and intracellular acidification will help to elucidate the complex mechanism of glycolysis under hypoxia. However, current studies are mainly focused on overexpression of intracellular reductases accelerated by hypoxia, and the investigations focusing on the relationship between hypoxic degree and intracellular acidification remain to be explored. For this vacuity, we report herein a new activatable nanoprobe for sensing pH change under different degrees of hypoxia by surface-enhanced Raman spectroscopy (SERS). The monitoring was based on the SERS spectra changes of 4-nitrothiophenol (4-NTP)-functionalized gold nanorods (AuNR@4-NTP) resulting from the nitroreductase (NTR)-triggered reduction under hypoxic conditions while the as-generated 4-aminothiophenol (4-ATP) is a pH-sensitive molecule. This unique property can ensure the SERS monitoring of intracellular acidification in living cells and tissues under hypoxic conditions. Dynamic pH analysis indicated that the pH decreased from 7.1 to 6.5 as a function of different degrees of hypoxia (from 15 to 1%) due to excessive glycolytic activity triggered by hypoxia. Given the known advantages of SERS sensing, these findings hold promise in studies of pathophysiological pathways involving hypoxia.

•A new label-free fluorescent method is proposed for Cu2+ detection.•Cu2+ can be detected by a one-step manner.•Attractively, the detection process is ultrafast; there is an absolute selectivity and zero-background interference.•The method can be practically applied for Cu2+ monitoring in real drinking and environmental water; and good potential has been verified for Cu2+ toxicides screening.Copper pollution has become more and more serious in modern society as the increasing industrial emission and the acid mine drainage, and exposure to excess copper can result in damage to living organisms. Thus, the development of efficient strategy for copper ion (Cu2+) detection is very essential and significant. Here, a high-efficiency fluorescent method is proposed for Cu2+ monitoring. The detection mechanism is based on the in situ formation of fluorescent copper nanoparticles (CuNPs). When the water sample is polluted by Cu2+, fluorescence emission of CuNPs can be observed by a one-step manner, and the emission intensity is proportional to Cu2+ concentration. Attractively, besides its advantages in operation and good detection capability, the generation of fluorescent signal is ultrafast, with a good signal response in 1 min; and there is no interference from background and other ions due to the in situ formation of signal unit. By virtue of its advantages, this strategy has been used to detect Cu2+ from polluted tap and river water samples, good performances demonstrate that the proposed method can be practically applied for Cu2+ monitoring in real drinking and environmental water. Simultaneously, great potential for Cu2+ toxicides screening has been verified by direct analysis of the effects of different model molecules on Cu2+, which will contribute to Cu2+-related sewage treatment and medical therapy.

Targeting nanocontainers to the pathological zone and controlling release of their cargoes, in particular delivery of anticancer drugs to specific tumor cells in a targeted and controlled manner, remain the key challenges in drug delivery. This paper reports the development of a traceable and tumor-targeted intracellular drug release nanocontainer. The nanocontainer is obtained by in situ growth of silver nanoparticles (AgNPs) on the surfaces of mesoporous silica nanospheres (MSNs) using a DNA-templated process. Additionally, drug release from the nanopores is achieved by selective glutathione (GSH)-triggered dismantle of the AgNPs, and the concurrent fluorescence change allows real-time monitoring of drug release efficacy and facile visualization of in vivo delivery events. After being functionalized with sgc8 aptamer on the outer shell of the AgNPs, the targeted nanocontainers are delivered into acute lymphoblastic leukemia cells by aptamer-mediated recognition and endocytosis. Moreover, the GSH-responsive process presents an improvement in the cell-specific drug release and chemotherapeutic inhibition of tumor growth.Keywords: DNA; drug delivery; glutathione; mesoporous silica nanoparticle; silver sphere;

Multifunctional nanoparticles integrated with an imaging module and therapeutic drugs are promising candidates for future cancer diagnosis and therapy. Mesoporous silica coated gold nanorods (AuNR@MS) have emerged as a novel multifunctional cancer theranostic platform combining the large specific surface area of mesoporous silica, which guarantees a high drug payload, and the photothermal modality of AuNRs. However, premature release and side effects of exogenous stimulus still hinder the further application of AuNR@MS. To address these issues, herein, we proposed a glutathione (GSH)-responsive multifunctional AuNR@MS nanocarrier with in situ formed silver nanoparticles (AgNPs) as the capping agent. The inner AuNR core functions as a hyperthermia agent, while the outer mesoporous silica shell exhibits the potential to allow a high drug payload, thus posing itself as an effective drug carrier. With the incorporation of targeting aptamers, the constructed nanocarriers show drug release in accordance with an intracellular GSH level with maximum drug release into tumors and minimum systemic release in the blood. Meanwhile, the photothermal effect of the AuNRs upon application to near-infrared (NIR) light led to a rapid rise in the local temperature, resulting in an enhanced cell cytotoxicity. Such a versatile theranostic system as AuNR@MS@AgNPs is expected to have a wide biomedical application and may be particularly useful for cancer therapy.Keywords: gold nanorods; GSH; mesoporous silica nanoparticles; photodynamic therapy; photothermal therapy; silver nanoparticle

One main source of cyanide (CN–) exposure for mammals is through the plant consumption, and thus, sensitive and selective CN– detection in plants tissue is a significant and urgent work. Although various fluorescence probes have been reported for CN– in water and mammalian cells, the detection of endogenous biological CN– in plant tissue remains to be explored due to the high background signal and large thickness of plant tissue that hamper the effective application of traditional one-photo excitation. To address these issues, we developed a new two-photo excitation (TPE) nanosensor using graphene quantum dots (GQDs)/gold nanoparticle (AuNPs) conjugate for sensing and imaging endogenous biological CN–. With the benefit of the high quenching efficiency of AuNPs and excellent two-photon properties of GQDs, our sensing system can achieve a low detection limit of 0.52 μM and deeper penetration depth (about 400 μm) without interference from background signals of a complex biological environment, thus realizing sensing and imaging of CN– in different types of plant tissues and even monitoring CN– removal in food processing. To the best of our knowledge, this is the first time for fluorescent sensing and imaging of CN– in plant tissues. Moreover, our design also provides a new model scheme for the development of two-photon fluorescent nanomaterial, which is expected to hold great potential for food processing and safety testing.Keywords: cyanide; gold nanoparticle; graphene quantum dot; imaging; plant tissue; two-photon

Intracellular pH is an important parameter associated with cellular behaviors and pathological conditions. Quantitative sensing pH and monitoring its changes by near-infrared (NIR) fluorescence imaging with high resolution in living systems are essential but challenging due to the lack of effective probes. To achieve good adaptability, in this study, a class of resolution-tunable ratiometric NIR fluorescent probes, which possess a stable NIR hemicyanine skeleton bearing different substituents, are rationally designed and synthesized, enabling detection through noninvasive optical imaging of organisms. Based on the protonation/deprotonation of the hydroxy group, a marked NIR emission shift provides a ratio signal in response to pH. Meanwhile, two states exhibit good photostability, sensitivity and reversibility, conducive to longtime monitoring of persistent pH changes without disturbance of other biological active species. Among the series, NIR-Ratio-BTZ modified with an electron-withdrawing substituent of benzothiazole exhibited the largest emission shift of about 76 nm from 672 to 748 nm with the pH environment changing from acidic to basic, which could be considered as a good candidate for high resolution pH imaging in live cells, tissues and organisms. Moreover, NIR-Ratio-BTZ has an ideal pKa value (pKa ≈ 7.2) for monitoring the minor fluctuations of physiological pH near neutrality. The ratiometric fluorescence measurement is beneficial to ensure the accuracy of quantitative measuring pH changes, as well as the real-time monitoring pH-related physiological effects both in living cells and living mice. The results demonstrate that NIR-Ratio-BTZ is a highly sensitive ratiometric pH probe in vivo, giving it potential for biological applications.

Methylmercury (CH3Hg+), the common organic source of mercury, is well-known as one of the most toxic compounds that is more toxic than inorganic or elemental mercury. In seabeds, the deposited Hg2+ ions are converted into CH3Hg+ by bacteria, where they are subsequently consumed and bioaccumulated in the tissue of fish, and finally, to enter the human diet, causing severe health problems. Therefore, sensitive and selective detection of bioaccumulation of CH3Hg+ in fish samples is desirable. However, selective assay of CH3Hg+ in the mercury-containing samples has been seriously hampered by the difficulty to distinguish CH3Hg+ from ionic mercury. We report here that metal amalgamation, a natural phenomenon occurring between mercury atoms and certain metal atoms, combining with DNA-protected silver nanoparticles, can be used to detect CH3Hg+ with high sensitivity and superior selectivity over Hg2+ and other heavy metals. In our proposed approach, discrimination between CH3Hg+ and Hg2+ ions was realized by forming Ag/Hg amalgam with a CH3Hg+-specific scaffold. We have found that Ag/Hg amalgam can be formed on a CH3Hg+-specific DNA template between silver atoms and mercury atoms but cannot between silver atoms and CH3Hg+. With a dye-labeled DNA strand, the sensor can detect CH3Hg+ down to the picomolar level, which is >125-fold sensitive over Hg2+. Moreover, the presence of 50-fold Hg2+ and 106-fold other metal ions do not interfere with the CH3Hg+ detection. The results shown herein have important implications for the fast, easy, and selective detection and monitoring of CH3Hg+ in environmental and biological samples.

•This two-photon probe exhibits an improved sensitivity and response time to H2S.•This probe shows excellent membrane permeability and fast visualization of H2S in living cells and tissues.•This probe is successfully applied to measure the endogenously produced H2S levels in different viscera of mouse.Development of efficient methods for detection of endogenous H2S in living cells and tissues is of considerable significance for better understanding the biological and pathological functions of H2S. Two-photon (TP) fluorescent probes are favorable as powerful molecular tools for studying physiological process due to its non-invasiveness, high spatiotemporal resolution and deep-tissues imaging. Up to date, several TP probes for intracellular H2S imaging have been designed, but real-time imaging of endogenous H2S-related biological processes in tissues is hampered due to low sensitivity, long response time and interference from other biothiols. To address this issue, we herein report a novel two-photon fluorescent probe (TPP-H2S) for highly sensitive and fast monitoring and imaging H2S levels in living cells and tissues. In the presence of H2S, it exhibits obviously improved sensitivity (LOD: 0.12 μM) and fast response time (about 2 min) compared with the reported two-photon H2S probes. With two-photon excitation, TPP-H2S displays high signal-to-noise ratio and sensitivity even no interference in cell growth media. As further application, TPP-H2S is applied for fast imaging of H2S in living cells and different fresh tissues by two-photon confocal microscope. Most importantly we first measured the endogenous H2S level in different viscera by vivisection and found that the distribution of endogenous H2S mostly in brain, liver and lung. The excellent sensing properties of TPP-H2S make it a practically useful tool for further studying biological roles of H2S.

Fluorescent chemodosimeters for a fluoride ion (F–) based on a specifically F–-triggered chemical reaction are characterized by high selectivity. However, they are also subjected to intrinsic limits, such as long response time, poor stability under aqueous solution, and unpredictable cell-member penetration. To address these issues, we reported here that the self-assembly of fluorescent chemodosimeter molecules on a graphene oxide (GO) surface can solve these problems by taking advantage of the excellent chemical catalysis and nanocarrier functions of GO. As a proof of concept, a new F–-specific fluorescent chemodosimeter molecule, FC-A, and the GO self-assembly structure of GO/FC-A were synthesized and characterized. Fluorescent sensing and imaging of F– with FC-A and GO/FC-A were performed. The results showed that the reaction rate constant of GO/FC-A for F– is about 5-fold larger than that of FC-A, so that the response time was shortened from 4 h to about 30 min, while for F–, the response sensitivity of GO/FC-A was >2-fold higher than that of FC-A. Furthermore, GO/FC-A showed a better bioimaging performance for F– than FC-A because of the nanocarrier function of GO for cells. It is demonstrated that this GO-based strategy is feasible and general, which could help in the exploration of the development of more effective fluorescent nanodosimeters for other analytes of interest.Keywords: biosensing and bioimaging; fluorescent chemodosimeter; fluoride ion; graphene oxide;

A novel two-photon absorption (TPA) nanomicelle through the “host-guest” chemistry has been developed and successfully applied in tumor tissue imaging in this work.

A growing body of evidence suggests that hydrogen peroxide (H2O2) plays an active role in the regulation of various physiological processes. Development of sensitive probes for H2O2 is an urgent work. In this study, we proposed a DNA-mediated silver nanoparticle and graphene quantum dot hybrid nanocomposite (AgNP-DNA@GQDs) for sensitive fluorescent detection of H2O2. The sensing mechanism is based on the etching effect of H2O2 to AgNPs and the cleavage of DNA by as-generated hydroxyl radicals (•OH). The formation of AgNP-DNA@GQDs nanocomposite can result in fluorescence quenching of GQDs by AgNPs through the resonance energy transfer. Upon H2O2 addition, the energy transfer between AgNPs and GQDs mediated by DNA was weakened and obvious fluorescence recovery of GQDs could be observed. It is worth noting that the reaction product •OH between H2O2 and AgNPs could cleave the DNA-bridge and result in the disassembly of AgNP-DNA@GQDs to achieve further signal enhancement. With optimal conditions, the approach achieves a low detection limit of 0.10 μM for H2O2. Moreover, this nanocomposite is further extended to the glucose sensing in human urine combining with glucose oxidase (GOx) for the oxidation of glucose and formation of H2O2. The glucose concentrations in human urine are detected with satisfactory recoveries of 94.6–98.8% which holds potential for ultrasensitive quantitative analysis of glucose and supplies valuable information for diabetes mellitus research and clinical diagnosis.

Using photons as external triggers to realize remote-controlled release of oligonucleotide is superior to other intracellular or external stimulus. UV light is a valid photon-controlled manner due to high efficiency. However, further applications of these approaches in living cells are hampered by the large dose of UV-light irradiation. To address this issue, a simultaneous light and host/guest mediation was proposed in this paper. Gold nanoparticles (AuNPs) encoding with mercapto-β-cyclodextrin (βCD) served as a carried agent. Azobenzene (Azo), which was labeled on a releasing oligonucleotide, acted as a photochemically controlled switch. Ferrocene (Fc), an excellent guest for inclusion complexation by βCD, serves as “enhancers” and shifts the equilibrium of the inclusion–exclusion process between trans-Azo and βCD under UV-light irradiation, thus making the dose of UV-light irradiation reduced obviously. For further application, transfected green fluorescent protein (GFP)-expressing human lung cancer A549 cells were used to determine cellular uptake and gene silencing mediated by our constructed system in vivo. The results demonstrate that by employing Fc host–guest interaction, about 62.4% gene silencing was achieved within 30 min, which is significantly higher than that without Fc competition. Our strategy provides the potential for orthogonal DNA delivery and therapeutic activation that would be capable of achieving higher levels of site-specific activity and reduced amounts of side effects.

Up to now, the successful fabrication of efficient hot-spot substrates for surface-enhanced Raman scattering (SERS) remains an unsolved problem. To address this issue, we describe herein a universal aptamer-based SERS biodetection approach that uses a single-stranded DNA as a universal trigger (UT) to induce SERS-active hot-spot formation, allowing, in turn, detection of a broad range of targets. More specifically, interaction between the aptamer probe and its target perturbs a triple-helix aptamer/UT structure in a manner that activates a hybridization chain reaction (HCR) among three short DNA building blocks that self-assemble into a long DNA polymer. The SERS-active hot-spots are formed by conjugating 4-aminobenzenethiol (4-ABT)-encoded gold nanoparticles with the DNA polymer through a specific Au–S bond. As proof-of-principle, we used this approach to quantify multiple target analytes, including thrombin, adenosine, and CEM cancer cells, achieving lowest limit of detection values of 18 pM, 1.5 nM, and 10 cells/mL, respectively. As a universal SERS detector, this prototype can be applied to many other target analytes through the use of suitable DNA-functional partners, thus inspiring new designs and applications of SERS for bioanalysis.

Inner filter effect (IFE), a well-known phenomenon of fluorescence quenching resulting from absorption of the excitation or emission light of luminescent species by absorbent, has been used as a smart approach to design fluorescent sensors, which are characterized by the simplicity and flexibility with high sensitivity. However, further application of IFE-based sensors in complex environment is hampered by the insufficient IFE efficiency and low sensitivity resulting from interference of the external environment. In this paper, we report that IFE occurring on a solid substrate surface would solve this problem. As a proof of concept, a fluorescent sensor for intracellular biothiols has been developed on the basis of the absorption of a newly designed thiols-specific chromogenic probe (CP) coupled with the use of a thiols-independent fluorophore, rhodamine 6G (R6G), operative on the IFE on graphene oxide (GO). To construct an efficient IFE system, R6G was covalently attached to GO, and the CP molecules were adsorbed on the surface of R6G-GO via π–π stacking interaction. The reaction of thiols with CP on R6G-GO decreases the absorption of CP, resulting in the increase of the intensity of R6G fluorescence. The results showed that the IFE efficiency, sensitivity, and dynamic response time of R6G-GO/CP for biothiols could be significantly improved compared with R6G/CP, and furthermore, R6G-GO/CP functioned under complex system and could be used for assaying biothiols in living cells and in human serum samples. This new strategy would be general to explore the development of more effective IFE-based sensors for other analytes of interest.

Molecular tools capable of providing information on a target analyte in an organelle of interest are especially appreciated. Traditionally, organelle-targetable probes are designed by incorporating an organelle-specific guiding unit to target the probe molecules into the organelle. The imperfect targeting function of the guiding unit and nonspecific distribution of the analyte in cytosol and each organelle would lead to low spatiotemporal resolution and limited sensitivity. To solve this problem, we report herein a new approach for detection of a target analyte in a specific organelle by engineering a target and location dual-controlled molecular switch. For this proof-of-concept study, fluorescent detection of H2S in lysosomes was performed with a simultaneous H2S and proton-activatable probe based on the acidic environment of lysosomes. The new synthesized fluorescent sensor, “SulpHensor”, which contains a spirolactam moiety to bind hydrogen protons and an azide group to react with H2S, displays highly sensitive and selective fluorescence response to H2S under lysosomal pH environment but is out of operation in neutral cytosol and other organelles. Fluorescence imaging shows that SulpHensor is membrane-permeable and suitable for visualization of both the exogenous and endogenous H2S in lysosomes of living cells. The good performance of our proposed approach for H2S sensing demonstrates that this strategy might open up new opportunities for the development of efficient subcellular molecular tools for bioanalytical and biomedical applications.

Two-photon excitation (TPE) with near-infrared (NIR) photons as the excitation source has important advantages over conventional one-photon excitation (OPE) in the field of biomedical imaging. β-cyclodextrin polymer (βCDP)-based two-photon absorption (TPA) fluorescent nanomicelle exhibits desirable two-photon-sensitized fluorescence properties, high photostability, high cell-permeability and excellent biocompatibility. By combination of the nanostructured two-photon dye (TPdye)/βCDP nanomicelle with the TPE technique, herein we have designed a TPdye/βCDP nanomicelle-based TPA fluorescent nanoconjugate for enzymatic activity assay in biological fluids, live cells and tissues. This sensing system is composed of a trans-4-[p-(N,N-diethylamino)styryl]-N-methylpyridinium iodide (DEASPI)/βCDP nanomicelle as TPA fluorophore and carrier vehicle for delivery of a specific peptide sequence to live cell through fast endocytosis, and an adamantine (Ad)-GRRRDEVDK-BHQ2 (black hole quencher 2) peptide (denoted as Ad-DEVD-BHQ2) anchored on the DEASPI/βCDP nanomicelle’s surface to form TPA DEASPI/βCDP@Ad-DEVD-BHQ2 nanoconjugate by the βCD/Ad host–guest inclusion strategy. Successful in vitro and in vivo enzymatic activities assay of caspase-3 was demonstrated with this sensing strategy. Our results reveal that this DEASPI/βCDP@Ad-DEVD-BHQ2 nanoconjugate not only is a robust, sensitive and selective sensor for quantitative assay of caspase-3 in the complex biological environment but also can be efficiently delivered into live cells as well as tissues and act as a “signal-on” fluorescent biosensor for specific, high-contrast imaging of enzymatic activities. This DEASPI/βCDP@Ad-DEVD-BHQ2 nanoconjugate provides a new opportunity to screen enzyme inhibitors and evaluate the apoptosis-associated disease progression. Moreover, our design also provides a methodology model scheme for development of future TPdye/βCDP nanomicelle-based two-photon fluorescent probes for in vitro or in vivo determination of biological or biologically relevant species.

•A novel dual-control activatable electron transfer strategy has been proposed.•A new β-galactosidase specific electrochemistry probe SP-β-gal has been designed.•The kinetics of β-galactosidase has been assayed using the proposed strategy.•β-galactosidase has been successfully detected in the 10% calf thymus.•SP-β-gal shows approximate performance with β-galactosidase staining kit.In traditional electrochemical sensors, the electrochemical signal transduction of the redox-active material is usually controlled by the analytical target. Due to non-specific interaction between the redox mediator and the target, false signal by single stimulus may not be avoided. To address this issue, we have developed a new electrochemical sensor that uses a functional spiropyran, an important class of photo and thermochromic compounds, as both recognition receptor and latent redox mediator, to realize simultaneous photochemical and target-modulated electron transfer. As a proof of principle, β-galactosidase was chosen as a model target. The new synthesized spiropyran probe, SP-β-gal, undergoes reversibly structural isomerization to form merocyanine under UV light irradiation. After the glycosidic bond being cleaved by β-galactosidase, the opened merocyanine of SP-β-gal forms redox-active 2-(2.5-dihydroxystyryl)-1.3.3-trimethyl-3H-indolium, and thus produces a pair of reversible redox current peaks under the electrochemical scanning. To amplify the detection signal, SP-β-gal was self-assembled with single-walled carbon nanotubes (SWCNTs) on the surface of glass carbon electrode. Kinetics experiments confirm that the probe is an ideal candidate for the determination of different concentrations of β-galactosidase digestion kinetics. Further, the SP-β-gal/SWCNTs-modified electrode is chemically stable in complex biological fluids. It was successfully applied to monitor β-galactosidase activity in the 10% calf thymus. This work represents not only a significant step forward in the further development of low-dimensional carbon nanomaterials/small organic molecular probes-based electrochemical biosensors, but also a new platform which may be extended to the assay of other enzyme such as β-d-glycosidase and so on by translating the biorecognition into electrochemical signal responses.

By engineering a gold nanoparticle and thymine–Hg2+–thymine-based hairpin DNA probe, a gold nanocarrier-based strategy for in vitro detection and live-cell imaging of thiol-containing amino acids/peptides was proposed.

In this communication, we molecularly engineered a light-switching excimer oligonucleotide-based probe for time-resolved fluorescent detection of Hg2+. By combining a time-resolved fluorescence technique and magnetic nanoparticles, Hg2+ spiked in human urine was detected.

Combining the inhibition of aptamer degradation with DNA Enzyme (DNAzyme) cascade-based signal amplification, a label-free and sensitive colorimetric protein assay strategy was proposed.

Fluorescence anisotropy (FA) is a reliable, sensitive, and robust assay approach for determination of many biological targets. However, it is generally not applicable for the assay of small molecules because their molecular masses are relatively too small to produce observable FA value changes. To address this issue, we report herein the development of a FA signal amplification strategy by employing graphene oxide (GO) as the signal amplifier. Because of the extraordinarily larger volume of GO, the fluorophore exhibits very high polarization when bound to GO. Conversely, low polarization is observed when the fluorophore is dissociated from the GO. As proof-of-principle, the approach was applied to FA detection of adenosine triphosphate (ATP) with a fluorescent aptamer. The aptamer exhibits very high polarization when bound to GO, while the FA is greatly reduced when the aptamer complexes with ATP, which exhibits a maximum signal change of 0.316 and a low detection limit of 100 nM ATP in buffer solution. Successful application of this strategy has been demonstrated that it can be constructed either in a “signal-off” or in a “signal-on” detection scheme. Moreover, because FA is less affected by environmental interferences, FA measurements could be conveniently used to directly detect as low as 1.0 μM adenosine triphosphate (ATP) in human serum. The universality of the approach could be achieved to detect an array of biological analytes when complemented with the use of functional DNA structures.

Heavy metal ion pollution poses severe risks in human health and the environment. Driven by the need to detect trace amounts of mercury, this article demonstrates, for the first time, that silver/mercury amalgamation, combining with DNA-protected silver nanoparticles (AgNPs), can be used for rapid, easy and reliable screening of Hg2+ ions with high sensitivity and selectivity over competing analytes. In our proposed approach, Hg2+ detection is achieved by reducing the mercury species to elemental mercury, silver atoms were chosen as the mercury atoms’ acceptors by forming Ag/Hg amalgam. To signal fluorescently this silver amalgamation event, a FAM-labeled ssDNA was employed as the signal reporter. AgNPs were grown on the DNA strand that resulted in greatly quenching the FAM fluorescence. Formation of Ag/Hg amalgam suppresses AgNPs growth on the DNA, leading to fluorescence signal increase relative to the fluorescence without Hg2+ ions, as well as marked by fluorescence quenching. This FAM fluorescence enhancement can be used for detection of Hg2+ at the a few nanomolar level. Moreover, due to excellent specificity of silver amalgamation with mercury, the sensing system is highly selective for Hg2+ and does not respond to other metal ions with up to millimolar concentration levels. This sensor is successfully applied to determination of Hg2+ in tap water, spring water and river water samples. The results shown herein have important implications in the development of new fluorescent sensors for the fast, easy, and selective detection and quantification of Hg2+ in environmental and biological samples.

Fluoride ion (F–), the smallest anion, exhibits considerable significance in a wide range of environmental and biochemical processes. To address the two fundamental and unsolved issues of current F– sensors based on the specific chemical reaction (i.e., the long response time and low sensitivity) and as a part of our ongoing interest in the spiropyran sensor design, we reported here a new F– sensing approach that, via assembly of a F–-specific silyl-appended spiropyran dye with graphene oxide (GO), allows rapid and sensitive detection of F– in aqueous solution. 6-(tert-Butyldimethylsilyloxy)-1′,3′,3′-trimethylspiro [chromene- 2,2′-indoline] (SPS), a spiropyran-based silylated dye with a unique reaction activity for F–, was designed and synthesized. The nucleophilic substitution reaction between SPS and F– triggers cleavage of the Si–O bond to promote the closed spiropyran to convert to its opened merocyanine form, leading to the color changing from colorless to orange-yellow with good selectivity over other anions. With the aid of GO, the response time of SPS for F– was shortened from 180 to 30 min, and the detection limit was lowered more than 1 order of magnitude compared to the free SPS. Furthermore, due to the protective effect of nanomaterials, the SPS/GO nanocomposite can function in a complex biological environment. The SPS/GO nanocomposite was characterized by XPS and AFM, etc., and the mechanism for sensing F– was studied by 1H NMR and ESI-MS. Finally, this SPS/GO nanocomposite was successfully applied to monitoring F– in the serum.

•We assembled split aptamer and γ-cyclodextrin fluorescence biosensors for ATP detection.•The biosensor increased quantum yield and emission lifetime of the excimer.•Time-resolved fluorescence is effective for ATP assay in complicated environment.A highly sensitive and selective fluorescence aptamer biosensors for the determination of adenosine triphosphate (ATP) was developed. Binding of a target with splitting aptamers labeled with pyrene molecules form stable pyrene dimer in the γ-cyclodextrin (γ-CD) cavity, yielding a strong excimer emission. We have found that inclusion of pyrene dimer in γ-cyclodextrin cavity not only exhibits additive increases in quantum yield and emission lifetime of the excimer, but also facilitates target-induced fusion of the splitting aptamers to form the aptamer/target complex. As proof-of-principle, the approach was applied to fluorescence detection of adenosine triphosphate. With an anti-ATP aptamer, the approach exhibits excimer fluorescence response toward ATP with a maximum signal-to-background ratio of 32.1 and remarkably low detection limit of 80 nM ATP in buffer solution. Moreover, due to the additive fluorescence lifetime of excimer induced by γ-cyclodextrin, time-resolved measurements could be conveniently used to detect as low as 0.5 μM ATP in blood serum quantitatively.Adenosine-binding aptamer was splitted into two fragments P2 and P3 which labeled pyrene molecules, mainly produce monomer signal. γ-CD cavity brings P2 and P3 in close proximity, allowing for weak excimer emission. In the presence of target, P2 and P3 are expected to bind ATP and form an aptamer/target complex, leads to large increase of the pyrene excimer fluorescence.

A new colorimetric and fluorescent probe, 2-(2,4-dinitrostyryl)-1,3,3-trimethyl-3H-indolium iodide (DTI), for selective and sensitive detection of biological thiols is reported. In aqueous solution at physiological pH 7.4, biological thiols react with DTI via Michael addition to give the brownish red adduct concomitant with fluorescence emission decrease.Biological thiols could be detected in 100% aqueous solution with high selectivity and sensitivity in physiological pH conditions.

Based on their enhanced cellular uptake, stability, biocompatibility, and versatile surface functionalization, spherical nucleic acids (SNAs) have become a potentially useful platform in biological applications. It still remains important to expand the SNAs’ “toolbox”, especially given the current interest in multimodal or theranostic nanomaterials, that is, composites capable of multiple simultaneous applications such as imaging, sensing, and drug delivery. In this paper, we have engineered a nanoparticle-conjugated initiator that triggers a cascade of hybridization reactions resulting in the formation of a long DNA polymer as the nanoparticle shell. By employing different DNA fragments, self-assembled multifunctional SNAs can be constructed. Therefore, using one capped ligand, these SNAs can combine imaging fluorescent tags, target recognition element, and targeted delivery molecules together. Since these SNAs possess high drug loading capacity and high specificity by the incorporation of an aptamer, our approach might find potential applications in new drug development, existing drug improvement, and drug delivery for cancer therapy.Keywords: cancer therapy; DNA hybridization reaction; DNA polymer; drug delivery; spherical nucleic acids

A DNA configuration switch is designed to fabricate a reversible and regenerable Raman-active substrate. The substrate is composed of a Au film and a hairpin-shaped DNA strand (hot-spot-generation probes, HSGPs) labeled with dye-functionalized silver nanoparticles (AgNPs). Another ssDNA that recognizes a specific trigger is used as an antenna. The HSGPs are immobilized on the Au film to draw the dye-functionalized AgNPs close to the Au surface and create an intense electromagnetic field. Hybridization of HSGP with the two arm segments of the antenna forms a triplex-stem structure to separate the dye-functionalized AgNPs from the Au surface, quenching the Raman signal. Interaction with its trigger releases the antenna from the triplex-stem structure, and the hairpin structure of the HSGP is restored, creating an effective “off–on” Raman signal switch. Nucleic acid sequences associated with the HIV-1 U5 long terminal repeat sequences and ATP are used as the triggers. The substrate shows excellent reversibility, reproducibility, and controllability of surface-enhanced Raman scattering (SERS) effects, which are significant requirements for practical SERS sensor applications.

Combining a DNA intercalator, SYBR Green I, and enzyme-linkage reactions with carbon nanoparticles, a low-background biosensing platform for label-free and sensitive fluorescent assay of DNA methylation is reported.

Combining the specific recognization of MutS protein for mismatched DNA sequences with the target-driven molecular switch that acts as both the template and primer of the polymerization reaction, a new label-free and sensitive fluorescent assay strategy for specific single-stranded DNA sequences or SNPs is proposed.

Complementary electrostatic interaction between the zwitterionic merocyanine and dipolar molecules has emerged as a common strategy for reversibly structural conversion of spiropyrans. Herein, we report a concept-new approach for thermal switching of a spiropyran that is based on simultaneous nucleophilic-substitution reaction and electrostatic interaction. The nucleophilic-substitution at spiro-carbon atom of a spiropyran is promoted due to electron-deficient interaction induced by 6- and 8-nitro groups, which is responsible for the isomerization of the spiropyran by interacting with thiol-containing amino acids. Further, the electrostatic interaction between the zwitterionic merocyanine and the amino acids would accelerate the structural conversion. As proof-of-principle, we outline the route to glutathione (GSH)-induced ring-opening of 6,8-dinitro-1′,3′,3′-trimethylspiro [2H-1-benzopyran-2,2′-indoline] (1) and its application for rapid and sensitive colorimetric detection of GSH. In ethanol–water (1:99, v/v) solution at pH 8.0, the free 1 exhibited slight-yellow color, but the color changed clearly from slight-yellow to orange-yellow when GSH was introduced into the solution. Ring-opening rate of 1 upon accession of GSH in the dark is 0.45 s–1, which is 4 orders of magnitude faster in comparison with the rate of the spontaneous thermal isomerization. The absorbance enhancement of 1 at 480 nm was in proportion to the GSH concentration of 2.5 × 10–8–5.0 × 10–6 M with a detection limit of 1.0 × 10–8 M. Furthermore, due to the specific chemical reaction between the probe and target, color change of 1 is highly selective for thiol-containing amino acids; interferences from other biologically active amino acids or anions are minimal.

A new approach for simple and rapid colorimetric detection of Hg2+ in aqueous solution is proposed based on Hg2+-induced aggregation of mononucleotides-stabilized gold nanoparticles.

On the basis of simultaneous electrostatic repulsion and π–π stacking interactions of carboxylic carbon nanoparticles (cCNPs) with single-stranded DNA, a noncovalent assembly of cCNPs and fluorescent aptamers is reported for rapid, sensitive, and selective detection of thrombin.

We report here a carbon nanotube-based approach for label-free and time-resolved luminescent assay of lysozyme (LYS) by engineering an antilysozyme aptamer and luminescent europium(III) (Eu3+) complex. The sensing mechanism of the approach is based on the exceptional quenching capability of carbon nanotubes for the proximate luminescent Eu3+ complex and different propensities of single-stranded DNA and the DNA/protein complex to adsorb on carbon nanotubes. The luminescence of a mixture of chlorosulfonylated tetradentate β-diketone−Eu3+ and the antilysozyme aptamer was efficiently quenched by single-walled carbon nanotubes (SWNTs) unless the aptamer interacted with LYS. Due to the highly specific recognition ability of the aptamer for the target and the powerful quenching property of SWNTs for luminescence regents, this proposed approach has a good selectivity and high sensitivity for LYS. In the optimum conditions described, >700-fold signal enhancement was achieved for micromolar LYS, and a limit of detection as low as 0.9 nM was obtained, which is about 60-fold lower than those of commonly used fluorescent aptamer sensors. Moreover, due to the much longer lifetime of the Eu3+ luminescence than those of the ubiquitous endogenous fluorescent components, the time-resolved luminescence technique could be conveniently used for application in complicated biological samples. LYS concentrations in human urine were thus detected using time-resolved luminescence measurement with satisfactory recoveries of 95−98%.

Ultrasensitive fluorescent analysis or monitoring of significant molecules in complex samples is important for many biological studies, clinical diagnosis, and forensic investigations, the major obstacle for which is the background signals from ubiquitous endogenous fluorescent components of the environments. Herein, a room-temperature phosphorescence (RTP)-based molecular beacon (MB), employing a Eu3+ complex of chlorosulfonylated tetradentate β-diketone (L) and the quencher BHQ-2, was engineered for highly sensitive detection of DNA sequences in biological fluids. Complexation of Eu3+ with the ligand L formed a strongly luminescent complex EuL2. But when EuL2 and BHQ-2 were labeled to two ends of a DNA molecule with hairpin structure, the luminescence of EuL2 was quenched by BHQ-2 due to the stem-closed conformation of the beacon. Due to very low background luminescence from the probe molecule, >200-fold signal enhancement was achieved when nanomolar target sequence was introduced. This sensitivity is about 20-fold higher than the level achieved with conventional fluorescence-based molecular beacons. Furthermore, because the Eu3+ complex has a much longer luminescence lifetime (≈0.8 ms) than that of the background (<10 ns), RTP measurements were used to directly detect as low as 500 pM DNA in cell media quantitatively without any sample pretreatment.

Despite that considerable efforts have been devoted to the design of various fluorogenic enzyme substrates, they are single-enzyme assay approaches that cannot afford detection of multienzyme activity. In this study, we set out our first attempt to design a new probe that could measure intracellular β-d-glucosidase and phosphodiesterase I activities. Unlike the commonly used fluorogenic enzyme substrates that contain one recognition site and signaling reporter, the new probe molecule possesses two cleavage sites, specificly corresponding to β-d-glucosidase and phosphodiesterase I, and three fluorescent reporters, 7-β-d-glucopyranosyloxycoumarin, 7-hydroxycoumarin, and meso-tetraphenylporphyrin. On the basis of intramolecular photoinduced electron transfer and fluorescence resonance energy transfer mechanisms, interaction of the probe with the two enzymes, whether only one or both, produces different signal readouts with high sensitivity. Remarkably, the probe is chemically stable in complex biological fluids. Fluorescence outputs are not significantly affected by biologically related metal ions, anions, amino acids, and proteins. Furthermore, fluorescence microscopy confirmed that the probe is an excellent candidate for intracellular delivery and can be accumulated intensively in cells. We demonstrated the applicability for the simultaneous images of intracellular β-d-glucosidase and phosphodiesterase I activities using the different optical imaging modes.

For successful assay development of an aptamer-based biosensor, various design principles and strategies, including a highly selective molecular recognition element and a novel signal transduction mechanism, have to be engineered together. Herein, we report a new type of aptamer-based sensing platform which is based on a triple-helix molecular switch (THMS). The THMS consists of a central, target specific aptamer sequence flanked by two arm segments and a dual-labeled oligonucleotide serving as a signal transduction probe (STP). The STP is doubly labeled with pyrene at the 5′- and 3′-end, respectively, and initially designed as a hairpin-shaped structure, thus, bringing the two pyrenes into spacer proximity. Bindings of two arm segments of the aptamer with the loop sequence of STP enforce the STP to form an “open” configuration. Formation of aptamer/target complex releases the STP, leading to new signal readout. To demonstrate the feasibility and universality of our design, three aptamers which bind to human α-thrombin (Tmb), adenosine triphosphate (ATP), and l-argininamide (L-Arm), respectively, were selected as models. The universality of the approach is achieved by virtue of altering the aptamer sequence without change of the triple-helix structure.

Inorganic nanomaterials have generated considerable interest in connection to the design of biosensors. Here we exploit the DNA-induced generation of silver nanoparticles for developing an electrical biosensing protocol for chloride ions. Conjugated with thiol modified oligonucleotide, silver nanoparticles were template-synthesized and immobilized on gold electrode. During cyclic voltammogram (CV) scans, the silver nanoparticles were oxidized at high potential to form a layer of Ag/AgCl complex in the presence of Cl−, giving off sharp solid state redox signals. Under the optimum condition, the electrode responded to Cl− over a dynamic range of 2.0 × 10−5–0.01 M, with a detection limit of 5.0 × 10−6 M. Moreover, the specific solubility product constant-based anion recognition made the electrode applicable at a wide pH range and in complex biological systems. To demonstrate the analytical applications of this sensor in real samples, the Cl− concentrations in human urine were measured without any sample pretreatment. Urinary Cl− detected by the proposed sensor ranged from 110 to 200 mM, which was comparable to the results obtained by standard silver titration.

To develop the high-performance fluorescent bio-sensors, the metal nanoparticles were employed as nanoquenchers and attracted reasonable attention in the design of fluorescent biosensors. In this work, silver nanoparticles (AgNPs) were obtained via reduction of Ag+ on FAM-labeled DNA template. For the tight binding between AgNPs and DNA, the template-synthesized AgNPs turned out high quenching efficiency and could be applied as super nanoquenchers to establish the biosensing platform for fluorescent detection. As an example, the template-synthesized DNA-AgNPs conjugates were employed in sensing thiols. By forming S-Ag bonds, thiols interact intensely with AgNPs and replace the FAM-labeled DNA off from the surface of AgNPs, resulting in a fluorescence enhancement. Besides the advantages of lower background and higher signal-to-background ratio (S/B), the conjugates present better stability, making them applicable in complicated biological fluids. To further evidence the feasibility of sensing thiols in real samples, the thiols in human urine were detected. The total amount of free thiols found in human urine was ranging from 229 μM to 302 μM with the proposed sensor. To conclude the reliability, low content of Cys was added and the recovery was 98%–103%.

Two new anthryl-appended porphyrin dyads have been synthesized and used as highly selective and sensitive fluorescence probes for singlet oxygen (1O2). The design strategy for the probes is directed by the idea of intramolecular fluorescence resonance energy transfer (FRET) interactions and carried out by incorporation of an electron-rich fluorophore (porphyrin) with a reactive anthracene for 1O2. The molecular recognition is based on the specific interaction of 1O2 with the inner anthracene moiety, and the signal reporter for the recognition process is the porphyrin fluorescence. As a result of overlap of the emission band of the anthracene with the absorbance band of the porphyrin, intramolecular FRET occurs between the anthracene (donor) and the porphyrin (acceptor). The effective light absorbed by the porphyrin and, concomitantly, the emitted light intensity are thus modulated by the emission intensity of the anthracene. Upon reaction with reactive oxygen species such as hydrogen peroxide, hypochlorite, superoxide, hydroxyl radicals, and 1O2, the probes exhibit a selective response toward 1O2. In addition, significant amplification of the signal transducer is observed. The feasibility of the design was demonstrated by monitoring the 1O2 generated from a MoO42−/H2O2 system. The results clearly demonstrate that the synthesized probes exhibit both high selectivity and high sensitivity for 1O2. The fluorescence reaction and signal amplification mechanism of the system were both discussed, clearly confirming that the introduction of electron-rich porphyrin units into the 9,10-positions of anthracene can improve the response sensitivity and activate the probe’s reactivity toward 1O2.

A highly sensitive and specific colorimetry-based rolling circle amplification (RCA) assay method for single-nucleotide polymorphism genotyping has been developed. A circular template is generated by ligation upon the recognition of a point mutation on DNA targets. An RCA amplification is then initiated using the circular template in the presence of Phi29 polymerase. The RCA product can be digested by a restricting endonuclease, and the cleaved DNA fragments can mediate the aggregation of gold nanoparticle-tagged DNA probes. This causes a colorimetric change of the solution as the indicator of the mutation occurrence, which can be detected using UV−vis spectroscopy or viewed by naked eyes. On the basis of the high amplification efficiency of Phi29 polymerase, a mutated target of ∼70 fM can be detected in this assay. In addition, the protection of the circle template using phosphorothioated nucleotides allows the digestion reaction to be performed simultaneously in RCA. Moreover, DNA ligase offers high fidelity in distinguishing the mismatched bases at the ligation site, resulting in positive detection of mutant targets even when the ratio of the wild-type to the mutant is 10 000:1. The developed RCA-based colorimetric detection scheme was demonstrated for SNP typing of β-thalassemia gene at position −28 in genomic DNA.

To construct efficient oligonucleotide probes, specific nucleic acid is designed as a conformationally constrained form based on the formation of a Watson−Crick-based duplex. However, instability of Watson−Crick hydrogen bonds in a complex biological environment usually leads to high background signal from the probe itself and false positive signal caused by nonspecific binding. To solve this problem, we propose a way to restrict the labeled-dyes in a hydrophobic cavity of cyclodextrin. This bounding, which acts like extra base pairs to form the Watson−Crick duplex, achieves variation of level of space proximity of the two labels and thus the degree of conformational constraint. To demonstrate the feasibility of the design, a stem-containing oligonucleotide probe (P1) for DNA hybridization assay and a stemless one (P2) for protein detection were examined as models. Both oligonucleotides were doubly labeled with pyrene at the 5′- and 3′- ends, respectively. It is the cyclodextrin/pyrene inclusion interaction that allows modulating the degree of conformational constraints of P1 and P2 and thus their background signals and selectivity. Under the optimal conditions, the ratio of signal-to-background of P1/γ-CD induced by 1.0 equiv target DNA is near 174, which is 4-fold higher than that in the absence of γ-CD. In addition, the usage of γ-CD shifts the melting temperature of P1 from 57 to 68 °C, which is reasonable for improving target-binding selectivity. This approach is simple in design, avoiding any variation of the stem’s length and sequences. Furthermore, the strategy is generalizable which is suited for not only the stem-containing probe but also the linear probe with comparable sensitivity and selectivity to conventional structured DNA probes.

In recent decades, numerous spiropyran derivatives have been designed and utilized for optical sensing of metal ions. However, there is still less research on spiropyran-based anion sensors. In this work, a new spiropyran compound (L) appended with a pendant bis(2-pyridylmethyl)amine was synthesized and used in fluorescent sensing of pyrophosphate ion (PPi) in aqueous solution. The molecular recognition and signal transduction are based on the cooperative ligation interactions and the ligation-induced structural conversion of the spiropyran, which leads to a significant change in the photophysical property of the spiropyran. In an ethanol/water solution (30:70, v/v) at pH 7.4, ligation of L with Zn2+ causes an intense fluorescence emission at 620 nm at the expense of the original fluorescence at 560 nm. Once PPi was introduced, interaction between PPi and the L−Zn2+ complex leads to full quenching of the 620 nm band emission which was concomitant with recovery of the 560 nm band emission, and the fluorescence intensity ratio, F560/F620, is proportional to the PPi concentration. Under the optimum condition, the L−Zn2+ complex responds to PPi over a dynamic range of 1.0 × 10−6 to 5.0 × 10−4 M, with a detection limit of 4.0 × 10−7 M. The fluorescence response is highly selective for PPi over other biologically related substrates, especially the structurally similar anions, such as phosphate and adenosine triphosphate. The mechanism of interaction among L, Zn2+, and PPi was primarily studied by 1H NMR, 31P NMR, and HRMS. To demonstrate the analytical application of this approach, the PPi concentration in human urine was determined. It was on the order of 3.18 × 10−5 M, and the mean value for urinary PPi excretion by three healthy subjects was 62.4 μmol/24 h.

Conformationally constraint nucleic acid probes were usually designed by forming an intramolecular duplex based on Watson−Crick hydrogen bonds. The disadvantages of these approaches are the inflexibility and instability in complex environment of the Watson−Crick-based duplex. We report that this hydrogen bonding pattern can be replaced by metal-ligation between specific metal ions and the natural bases. To demonstrate the feasibility of this principle, two linear oligonucleotides and silver ions were examined as models for DNA hybridization assay and adenosine triphosphate detection. The both nucleic acids contain target binding sequences in the middle and cytosine (C)-rich sequences at the lateral portions. The strong interaction between Ag+ ions and cytosines forms stable C−Ag+-C structures, which promises the oligonucleotides to form conformationally constraint formations. In the presence of its target, interaction between the loop sequences and the target unfolds the C−Ag+-C structures, and the corresponding probes unfolding can be detected by a change in their fluorescence emission. We discuss the thermodynamic and kinetic opportunities that are provided by using Ag+ ion complexes instead of traditional Watson−Crick-based duplex. In particular, the intrinsic feature of the metal-ligation motif facilitates the design of functional nucleic acids probes by independently varying the concentration of Ag+ ions in the medium.

A new fluorescent sensing approach for detection of single-nucleotide polymorphisms (SNPs) is proposed based on the ligase reaction and gold nanoparticle (AuNPs)-quenched fluorescent oligonucleotides. The design exploits the strong fluorescence quenching of AuNPs for organic dyes and the difference in noncovalent interactions of the nanoparticles with single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA), where ssDNA can be adsorbed onto the surface of AuNPs while dsDNA cannot be. In the assay, two half primer DNA probes, one being labeled with a dye and the other being phosphorylated, were first incubated with a target DNA template. In the presence of DNA ligase, the two captured ssDNAs are linked for the perfectly matched DNA target to form a stable duplex, but the duplex could not be formed by the single-base mismatched DNA template. After addition of AuNPs, the fluorescence of dye-tagged DNA probe will be efficiently quenched unless the perfectly matched DNA target is present. To demonstrate the feasibility of this design, the performance of SNP detection using two different DNA ligases, T4 DNA ligase and Escherichia coli DNA ligase, were investigated. In the case of T4 DNA ligase, the signal enhancement of the dye-tagged DNA for perfectly matched DNA target is 4.6-fold higher than that for the single-base mismatched DNA. While in the presence of E. coli DNA ligase, the value raises to be 30.2, suggesting excellent capability for SNP discrimination.

Using classic DNA-intercalating dye and carbon nanotubes, a simple, but efficient, method for fluorescent detection of DNA hybridization has been developed.

We report that the hydrogen-bonding pattern in a molecular beacon can be replaced by metal-dependent pairs of Hg2+ and DNA thymine (T) bases. A molecular beacon based on T–Hg2+–T exhibits a lower background signal and higher thermostability than regular molecular beacons.

A new strategy for molecular beacon binding readout is proposed by using separation of the molecular recognition element and signal reporter. The signal transduction of the target binding event is based on displacing interaction between the target DNA and a competitor, the signal transducer. The target-free capture DNA is first interacted with the competitor, forming an assembled complex. In the presence of a target DNA that the affinity is stronger than that of the competitor, hybridization between capture DNA and the target disassembles the assembled complex and releases the free competitor to change the readout of the signal reporter. To demonstrate the feasibility of the design, a thymine-rich oligonucleotide was examined as a model system. Hg2+ was selected as the competitor, and mercaptoacetic acid-coated CdTe/ZnS quantum dots served as the fluorescent reporter. Selective binding of Hg2+ between the two thymine bases of the capture DNA forms a hairpin-structure. Hybridization between the capture DNA and target DNA destroys the hairpin-structure, releasing Hg2+ ions to quench the quantum dots fluorescence. Under the optimal conditions, fluorescence intensity of the quantum dots against the concentration of perfect cDNA was linear over the concentration range of 0.1−1.6 μM, with a limit of detection of 25 nM. This new assay method is simple in design, avoiding any oligonucleotide labeling. Furthermore, this strategy is generalizable since any target binding can in principle release the signal transducer and be detected with separated signal reporter.

Spiropyrans are an attractive starting point in design of optical approaches for metal ions sensing. However, the high background in aqueous solution and non-specific chelation of the spiropyran with heavy metal ions has hindered their application as reliable sensors for environmental and biological species. Here, we report on a new spiropyran-based approach for sensitive and selective sensing of Hg2+ in aqueous solution, based on cooperative ligation interactions among the spiropyran probe, an intermediate, cysteine, and the metal ion. To test the feasibility of this design, three spiropyran scaffolds, L1–L3, with different ligation functions at the 8′-position were examined as model systems. The results demonstrate that by using cysteine, a potential ligand of Hg2+, the spiropyran could detect 1.0 × 10−7 M Hg2+ in aqueous solution. Due to the specific metal–amino acid interaction, the approach exhibits selective response toward Hg2+ over other metal ions and anions, although possible interference from Cu2+ has to be considered at the high level of the metal ion. This approach has been used for the determination of Hg2+ in water samples containing potential interferents with satisfactory recovery.

A single anthryl appended meso-tetraphenylporphyrin (TPP) dyad has been synthesized and applied in fluorescence sensing of iodine based on the intramolecular excitation energy transfer. The molecular recognition of the sensor is based on the interaction of iodine with inner anthracene moiety of the dyad, while the signal reporter for the recognition process is the TPP fluorescence quenching. Because the emission spectrum of anthracene is largely overlapped with the Soret band absorption of TPP, intramolecular excitation energy transfer interaction occurs between the donor, anthracene and acceptor, TPP. This energy transfer leads to TPP fluorescence emission by excitation of anthracene. The sensor was constructed by immobilizing the dyad in a plasticized poly(vinyl chloride) (PVC) membrane. The sensing membrane shows higher sensitivity compared to the sensors by using anthracene, TPP, or a mixture of anthracene and TPP as sensing materials. Under the optimum conditions, iodine in a sample solution can be determined from 2.04 to 23.6 mmol·L−1 with a detection limit of 33 nmol·L−1. The sensing membrane shows satisfactory response characteristics including good reproducibility, reversibility and stability, as well as the short response time of less than 60 s. Except for Cr2O72− and MnO4−, other common metal ions and anions in foodstuff do not interfere with iodine determination. The proposed method was applied in the determination of iodine in table salt samples. The results agree well with those obtained by other methods.

Four tetradentate β-diketonate–Eu3+ complexes were developed as probes for the luminescent sensing of multi-phosphates. By using an appropriate ligand, the pyrophosphate ion (PPi) could be selectively and sensitively detected.

An approach for visual and fluorescent sensing of Hg2+ in aqueous solution is presented. This method is based on the Hg2+-induced conformational change of a thymine (T)-rich single-stranded DNA (ssDNA) and the difference in electrostatic affinity between ssDNA and double-stranded (dsDNA) with gold nanoparticles. The dye-tagged ssDNA containing T−T mismatched sequences was chosen as Hg2+ acceptor. At high ionic strength, introduction of the ssDNA to a colloidal solution of the aggregates of gold nanoparticles results in color change, from blue-gray to red of the solution, and the fluorescence quenching of the dye. Binding of Hg2+ with the ssDNA forms the double-stranded structure. This formation of dsDNA reduces the capability to stabilize bare nanoparticles against salt-induced aggregation, remaining a blue-gray in the color of the solution, but fluorescence signal enhancement compared with that without Hg2+. With the optimum conditions described, the system exhibits a dynamic response range for Hg2+ from 9.6 × 10−8 to 6.4 × 10−6 M with a detection limit of 4.0 × 10−8 M. Both the color and fluorescence changes of the system are extremely specific for Hg2+ even in the presence of high concentrations of other heavy and transition metal ions, which meet the selective requirements for biomedical and environmental application. The combined data from transmission electron microscopy, fluorescence anisotropy measurements, and dialysis experiments indicate that both the color and the fluorescence emission changes of the DNA-functioned gold nanoparticles generated by Hg2+ are the results of the metal-induced formation of dsDNA and subsequent formation of nanoparticle aggregates.

α, β, γ, δ-Tetrakis(3,5-dibromo-2-hydroxylphenyl)porphyrin (TDBHPP) was synthesized and used for the fluorimetric determination of trace amount of lead ion in aqueous solution based on the inclusion interaction of the porphyrin with β-cyclodextrin (β-CD). In aqueous solution, the interaction of β-CD with TDBHPP caused a large enhancement of the porphyrin fluorescence intensity. In addition, the increased fluorescence of TDBHPP by β-CD was sensitive to metal ion following the fluorescence quenching of TDBHPP at its maximum emission wavelength. The quenching of TDBHPP fluorescence at room temperature was fast and nearly complete upon lead ion interaction. The organizing ability of the β-CD medium and the protection of the ligand from the micro-environment conferred in increased sensitivity, selectivity and detection limit, and allowed the determination of 2.8 × 10−7 to 7.4 × 10−5 mol/L lead compared with those obtained in the absence of β-CD. The method was applied in the analysis of synthetically biological samples with satisfactory results.

We report that the hydrogen-bonding pattern in a molecular beacon can be replaced by metal-dependent pairs of Hg2+ and DNA thymine (T) bases. A molecular beacon based on T–Hg2+–T exhibits a lower background signal and higher thermostability than regular molecular beacons.

Combining a DNA intercalator, SYBR Green I, and enzyme-linkage reactions with carbon nanoparticles, a low-background biosensing platform for label-free and sensitive fluorescent assay of DNA methylation is reported.

Combining the specific recognization of MutS protein for mismatched DNA sequences with the target-driven molecular switch that acts as both the template and primer of the polymerization reaction, a new label-free and sensitive fluorescent assay strategy for specific single-stranded DNA sequences or SNPs is proposed.

A ratiometric two-photon fluorescent probe for SO2 derivatives was first proposed based on acedan–merocyanine dyads via a TP-FRET strategy. It was successfully applied to visualization of the fluctuations of enzymatically generated SO2 derivatives in the mitochondria of HepG2 cells and rat liver tissues using two-photon fluorescence microscopy imaging.

A novel two-photon absorption (TPA) nanomicelle through the “host-guest” chemistry has been developed and successfully applied in tumor tissue imaging in this work.

A new approach for simple and rapid colorimetric detection of Hg2+ in aqueous solution is proposed based on Hg2+-induced aggregation of mononucleotides-stabilized gold nanoparticles.

Combining the inhibition of aptamer degradation with DNA Enzyme (DNAzyme) cascade-based signal amplification, a label-free and sensitive colorimetric protein assay strategy was proposed.

In this communication, we molecularly engineered a light-switching excimer oligonucleotide-based probe for time-resolved fluorescent detection of Hg2+. By combining a time-resolved fluorescence technique and magnetic nanoparticles, Hg2+ spiked in human urine was detected.

By engineering a gold nanoparticle and thymine–Hg2+–thymine-based hairpin DNA probe, a gold nanocarrier-based strategy for in vitro detection and live-cell imaging of thiol-containing amino acids/peptides was proposed.

Using classic DNA-intercalating dye and carbon nanotubes, a simple, but efficient, method for fluorescent detection of DNA hybridization has been developed.

Four tetradentate β-diketonate–Eu3+ complexes were developed as probes for the luminescent sensing of multi-phosphates. By using an appropriate ligand, the pyrophosphate ion (PPi) could be selectively and sensitively detected.

Nitric oxide (NO) is often involved in many different physiological processes including the regulation of lysosomal functions. However, it remains a great challenge to explore the variations of NO levels in lysosomes, limiting the understanding behind its biological functions in cellular signaling pathways and various diseases. Herein, a pH-activatable fluorescent probe, Rhod-H-NO, was designed and synthesized for the determination of lysosomal NO, in which the activation response model is beneficial towards getting accurate biological information. To ensure that Rhod-H-NO can accumulate effectively and exist stably in lysosomes without interference and degradation from other active species, Rhod-H-NO was engineered into the nanopores of mesoporous silica nanoparticles (MSNs) with β-cyclodextrin (β-CD) as the gatekeeper to obtain a nanolab. The nanolab was successfully applied to detect lysosomal NO in living cells and in vivo with high time and spatial resolution. This nanolab could serve as an excellent molecular tool to exploit and elucidate the function of NO at sub-cellular levels.

On the basis of simultaneous electrostatic repulsion and π–π stacking interactions of carboxylic carbon nanoparticles (cCNPs) with single-stranded DNA, a noncovalent assembly of cCNPs and fluorescent aptamers is reported for rapid, sensitive, and selective detection of thrombin.