AbstractThis study herein develops a novel tumor-targeting photothermal heating-responsive nanoplatform for enhanced photodynamic therapy (PDT). The nanoplatform is prepared by using dopamine-reduced graphene oxide nanosheets (rGO-PDA) to enhance photothermal ability, mesoporous silica coated on the rGO-PDA surface to load drug, and hyaluronic acid to act as gate keeper as well as targeting moiety. The developed nanoplatform has outstanding biocompatibility, well targeting ability, excellent near-infrared radiation (NIR) photothermal conversion ability, controllable drug release with NIR irradiation response, and the capacity of delivering diverse drugs. The proposed nanoplatform is successfully used to specifically deliver chlorin e6 (Ce6) to CD-44 over-expressing cancer cells for PDT with a loading capacity of 0.605 mg mg−1 and controllable Ce6 release with NIR irradiation response. The combination of excellent NIR photothermal conversion ability and controllable Ce6 release confers the nanoplatform with enhanced singlet oxygen generation, which leads to more significant destruction of target cancer cells. The prepared photothermal heating-responsive nanoplatform can enhance photodynamic therapeutic efficiency and hold great potential for multimodal cancer therapy.

•A MeHg ion-imprinted magnetic nanoparticle was developed for rapidly extract ultra-trace MeHg from water.•It has better stability, specificity and a 25 mg MeHg/g of adsorption capacity.•It can specifically extract MeHg from water within 30 min with a recovery >95% and a 250 enrichment factor.•It can be used for simple and accurate detection of trace MeHg in water by combining with CE-ICP-MS.For rapidly and sensitively determining ultra-trace methyl mercury (MeHg) in aqueous environment, we herein synthesized a MeHg ion-imprinted magnetic nanoparticle (MeHg IIMN) to simply and specifically extract/concentrate ultra-trace MeHg from water samples. The MeHg IIMN employed core-shell Fe3O4@SiO2 nanoparticles (Fe3O4@SiO2 NPs) as supporting structure, the complex ion of 1-pyrrolidinecarbodithioic acid and MeHg (PDC-CH3Hg+) as template, methacrylic acid (MAA) as functional monomer and trimethylolpropane trimethacrylate (TMPTM) as cross linker. The MeHg IIMN offered obvious advantages such as low cost, easy manipulation, better specificity and stability, and recycling characteristics. It can be used to separate/concentrate ultra-trace MeHg from natural water sample within 30 min with a recovery >95%, an enrichment factor of 250, a relative standard deviation (RSD, n = 5) <7%, a 25 mg MeHg/g of maximum adsorption capacity, 50 times of recycling, and without obvious interference of other ions. Combining with capillary electrophoresis-inductively coupled plasma mass spectrometry (CE-ICP-MS), it can be used for the accurate detection of ultra-trace methyl mercury in natural water samples with a limit of detection of 0.084 pg/mL, a recovery of 92–99% and a RSD (n = 5) <8%. The success of this study promises a valuable technique for relatively simple detection of ultra-trace methyl mercury in aqueous environment.

We herein reported on novel phosphatidylserine-functionalized Fe3O4@SiO2 NPs (nanoparticles) and enzyme-encapsulated liposomes for the visual detection of Cu2+ by employing phosphatidylserine for Cu2+ recognition and the enzymatic catalysis/oxidation of 3,3′,5,5′-tetramethylbenzidine sulfate (TMB) as a signal generator. Phosphatidylserine (1,2-dioleoyl-sn-glycero-3-phospho-L-serine, DOPS) was covalently assembled on the Fe3O4@SiO2 NP surface to obtain DOPS-functionalized Fe3O4@SiO2 NPs, and was used to encapsulate horseradish peroxidase (HRP) to form HRP-encapsulated DOPS liposomes. It was demonstrated that DOPS-functionalized Fe3O4@SiO2 NPs can specifically bind HRP-encapsulated DOPS liposomes in the presence of Cu2+ at basic pH. The HRP-encapsulated DOPS liposome bound on the DOPS-functionalized Fe3O4@SiO2 NPs was then separated from solution with a magnet. Upon the addition of TMB–H2O2 solution, the HRP-encapsulated DOPS liposome bound on the DOPS-functionalized Fe3O4@SiO2 NPs was broken to release HRP, and the released HRP catalyzes the H2O2-mediated oxidation of TMB, which gives rise to a change from colourless to blue in solution colour and a new absorption peak at 652 nm. This provided a sensing platform for the sensitive, specific and field-portable colorimetric detection of Cu2+. By using the sensing platform, a selective and sensitive visual sensor for the detection of Cu2+ was developed. The proposed method has outstanding advantages including adequate sensitivity (the sensitivity can be improved by using a greater volume of the water sample), shorter analysis time, relatively low cost, operation at room temperature and stronger resistibility to the matrix. It can be used to detect as little as 0.1–0.5 μM of Cu2+ in river water using naked-eye observation and 0.05 μM of Cu2+ in river water using UV-visible spectrophotometry when 2 mL of the water sample was used for detection, within 15 min and with a recovery of 95–101% and a RSD < 5% (n = 5). A visual detection limit of 0.1–0.5 μM is much lower than the maximum allowable level of Cu2+ (∼20 μM) in drinking water defined by the USA EPA. The above features make our sensor a promising approach for the rapid and on-site detection of trace free copper ions in aqueous environments by only naked-eye observation.

Early diagnostic methods are the most effective way to increase the survival rate of cancer patients. In this study, we present a novel method for sensitively and specifically counting cancer cells using a magnetic bead (MB)-based AuNP–aptamer labelling technique and inductively coupled plasma mass spectrometry (ICP-MS) detection. A MB-based AuNP–aptamer labelling technique can specifically recognize cancer cells and tag AuNPs to the cancer cells, which provides a platform for indirectly counting cancer cells via the detection of Au with ICP-MS. The method reported in this study combines the merits of a MB-based AuNP–aptamer labelling technique and ICP-MS detection, resulting in better specificity and stability, high sensitivity, short analysis time, and robust resistance to a complicated matrix. Especially, the employment of ICP-MS detection and the presence of MBs that facilitate the magnetic separation of target cells, not only greatly shorten the analysis time but also greatly enhance the resistance of our method to a complicated matrix. The proposed method can be used to count as few as 100 human hepatocellular carcinoma SMMC-7721 cells in 1 mL of serum with a recovery of 93–104% and a RSD < 4% (n = 5) within 3 hours. The success of this study provides a promising rapid approach for the early detection of human hepatocellular carcinoma cells in clinical diagnosis.

•A simple, cost-efficient and rapid determination method of baicalin is proposed.•The method is based on the MoS2 nano-sheets-modified glassy carbon electrode.•It was successfully applied to determine baicalin in pharmaceutical preparations.In this study, a molybdenum disulfide (MoS2) nano-sheets-modified glassy carbon electrode (GCE) was prepared, and the electrochemical behavior of baicalin on the proposed electrode was investigated by cyclic voltammetry (CV) in PBS buffer solution (pH 7.0). The experimental results showed that baicalin exhibits enhanced voltammetric response on the MoS2-modified GCE. Based on the enhanced voltammetric response of baicalin on the MoS2-modified GCE, a sensitive and selective electrochemical method for the determination of baicalin was developed by using differential pulse voltammetry (DPV). Various experimental parameters including the pH of supporting electrolyte, amount of MoS2 nano-sheets and accumulation time were optimized. Under the optimized conditions, the oxidation peak current was linearly proportional to the baicalin concentrations in the range of 1.25 × 10− 7 M–1.25 × 10− 5 M, and the detection limit (S/N = 3) was calculated to be 5.0 × 10− 8 M. The developed method was successfully used to detect baicalin in pharmaceutical samples with a recovery of 97–109% and a relative standard deviation (RSD, n = 6) < 6%.

To extract and pre-concentrate ultra-trace methyl mercury (MeHg) from natural water, a novel MeHg ion imprinted silica microsphere (MeHg IISM) was designed and synthesized by using silica microspheres as a supporting material, the complex ion of 1-pyrrolidinecarbodithioic acid and MeHg (PDC–CH3Hg+) as a template, methacrylic acid (MAA) as a functional monomer, azodiisobutyronitrile (AIBN) as an initiator, trimethylolpropane trimethacrylate (TMPTM) as a cross-linking agent and ethanol as a solvent. The as prepared MeHg IISM is easy to fabricate with low cost, and has excellent stability, specificity and adsorption capacity. It can be used to specifically extract and pre-concentrate ultra-trace MeHg from natural water samples with a recovery of 92–105%, a intraday relative standard deviation (RSD, n = 5) <5%, a inter-day RSD (n = 5) <7% and less interference of other ions within 30 min. The as prepared MeHg IISM can be repeatedly used more than 50 times with a 30 mg MeHg per gram adsorption capacity. Combined with ICP-MS, it can be used for the rapid and cost-effective detection of ultra-trace methyl mercury in natural water. The success of this study promises a valuable technique for rapid, low-cost extraction/pre-concentration and detection of ultra-trace methyl mercury in aqueous environments.

•A novel biosensor for the visual detection of trace UO22+ in aqueous environment was reported.•The biosensor employs DNAzyme-functionalized MBs for UO22+ recognition.•The biosensor is simple, rapid, cost-effective and has a high sensitivity and specificity.•It can be used to detect 0.02 ppb of UO22+ in aqueous environment by only naked-eye observation.We herein developed a novel biosensor for the visual detection of trace uranyl ion (UO22+) in aqueous environment with high sensitivity and specificity by using DNAzyme-functionalized magnetic beads (MBs) for UO22+ recognition and gold nano-particles (AuNPs)-based enzymatic catalysis oxidation of TMB (3,3′,5,5′-tetramethylbenzidine sulfate) for signal generation. The utilization of MBs facilitates the magnetic separation and collection of sensing system from complex sample solution, which leads to more convenient experimental operation and more strong resistibility of the biosensor to the matrix of sample, and the utilization of AuNPs-based enzymatic catalysis amplification greatly improved the sensitivity of the biosensor. Compared with the previous DNAzyme-based UO22+ sensors, the proposed biosensor has outstanding advantages such as relative high sensitivity and specificity, operation convenience, low cost and more strong resistibility to the matrix of sample. It can be used to detect as low as 0.02 ppb (74 pM) of UO22+ in aqueous environment by only naked-eye observation and 1.89 ppt (7.0 pM) of UO22+ by UV–visible spectrophotometer with a recovery of 93–99% and a RSD≤5.0% (n=6) within 3 h. Especially, the visual detection limit of 0.02 ppb (74 pM) is much lower than the maximum allowable level of UO22+ (130 nM) in the drinking water defined by the U.S. Environmental Protection Agency (EPA), indicating that our method meets the requirement of rapid and on-site detection of UO22+ in the aqueous environment by only naked-eye observation.

We herein reported a novel spiro-rhodamine B lactam derivative (RhBLA), which can be coupled to Fe3O4 nanoparticles (NPs) and act as a Cu2+-selective visual sensor. We demonstrated that the RhBLA-functionalized Fe3O4 NPs can specifically chelate with Cu2+ to create a colour change from colourless to pink, which provides a sensing platform for the simple, rapid and field-portable visual detection of trace Cu2+. By using this sensing platform, a sensitive and specific visual sensor for the rapid and on-site detection of trace Cu2+ was developed. The coupling of RhBLA to Fe3O4 NPs facilitates the magnetic separation of Cu2+ from a bulk sample solution, which leads to the selective detection of Cu2+ at low concentration and the robust resistibility of the sensor to the matrix of the sample. The proposed visual sensor can be used to directly detect as little as 50 nM of Cu2+, which is much lower than the maximum allowable level of Cu2+ (∼20 μM) in drinking water defined by the USA EPA, in 100 mL of river or tap water by only naked-eye observation within 15 min. In addition, the method proposed in this study is simple, cost effective, rapid, and does not need any sophisticated instruments. The above features make our sensor a promising approach for the rapid and on-site visual detection of ultra-trace free copper ions in aqueous environments by only naked-eye observation.

In this paper, we have reported on novel phosphatidylserine-functionalized AuNPs (gold nanoparticles) for the visual detection of Cu2+ by employing phosphatidylserine for Cu2+ recognition and AuNPs for signal generation. The phosphatidylserine (1,2-dioleoyl-sn-glycero-3-phospho-L-serine, DOPS) was covalently assembled on the AuNP surface to obtain DOPS-functionalized AuNPs. It was demonstrated that DOPS-functionalized AuNPs could specifically bind Cu2+ and lead to the aggregation of AuNPs, which gave rise to a colour change from wine-red to blue and a new absorption band around 650 nm. This provides a sensing platform for the simple, rapid and field portable colorimetric detection of Cu2+. By using the sensing platform, a selective and sensitive visual biosensor for the detection of Cu2+ was developed. The proposed biosensor has outstanding analytical advantages such as good stability, relatively high sensitivity, low cost and short analysis time. It can be used to detect concentrations of Cu2+ as low as 30 μM in river water by observation with the naked eye and of 1.55 μM Cu2+ in river water by UV-visible spectrophotometry, within 10 min and with a recovery of 98–103% and a relative standard deviation (RSD) < 4% (n = 6). The proposed biosensor is promising for on-site detection of trace Cu2+ in clinical diagnosis or environmental monitoring.

•An ultra-sensitive method for detecting lysozyme based on CE–ICP–MS was described.•The proposed method has an extremely low detection limit of 3.89 attomole.•It can be used to detect trace lysozyme in saliva sample with a satisfied recovery.•The method provides a new potential for sensitive detection of low-abundant proteins.In this study, an ultra-sensitive method for the quantification of lysozyme based on the Gd3+ diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid labeling and capillary electrophoresis–inductively coupled plasma mass spectrometry (CE–ICP–MS) was described. The Gd3+-tagged lysozyme was effectively separated by capillary electrophoresis (CE) and sensitively determined by inductively coupled plasma mass spectrometry (ICP–MS). Based on the gadolinium-tagging and CE–ICP–MS, the lysozyme was determined within 12 min with an extremely low detection limit of 3.89 attomole (3.89 × 10−11 mol L−1 for 100 nL of sample injection) and a RSD < 6% (n = 5). The proposed method has been successfully used to detect lysozyme in saliva samples with a recovery of 91–106%, suggesting that our method is sensitive and reliable. The success of the present method provides a new potential for the biological assays and sensitive detection of low-abundant proteins.An ultra-sensitive method for the determination of lysozyme was developed based on the Gd3+ chelate labeling and CE–ICP–MS. The proposed method has an extremely low detection limit of 3.89 attomole and has been successfully used to detect lysozyme in saliva sample, showing excellent reliability. The success of the present method provides a new possibility for biological assays and clinical diagnoses.

•A method for the simultaneous detection of 7 benzoylurea pesticides was reported.•The method can be used to detect 7 benzoylurea pesticides in tea and its infusion.•The leaching behaviour of benzoylurea pesticides in Oolong tea was also studied.•Two different leaching behaviours were observed for different benzoylurea pesticides.A method for the simultaneous determination of 7 benzoylurea pesticides (chlorfluazuron, diflubenzuron, fluazuron, flufenoxuron, hexaflumuron, teflubenzuron and triflumuron) in the manufactured Oolong tea leaves and its infusion was described. The method has a LOD of 0.03–1.00 ng/mL, a recovery of 90.4–103% for made tea and 90.3–102% for tea-infused liquid, respectively. By using the proposed method, the leaching characteristics of above 7 pesticides during infusing process were investigated. The experimental results revealed that: (1) diflubenzuron can be most easily extracted out during infusing process, followed by triflumuron, teflubenzuron, hexaflumuron, chlorfluazuron, flufenoxuron and fluazuron. (2) The leaching of flufenoxuron and chlorfluazuron during infusing process seems to be controlled by only their solubility, whereas, the leaching of other 5 benzoylurea insecticides was primarily controlled by their partitioning coefficient between made tea and hot water. The results of this study are helpful for the accurate evaluation of the safety of Oolong tea.

•A ICP-MS-based assay was developed for the specific and sensitive detection of DNA.•The assay employs ICP-MS detection together with MBs-based rolling circle amplification and AuNPs-aptamer labeling.•The method is simple, rapid, cost-effective and has a detection limit of 0.1 fM.•The assay has an excellent discriminating ability for single-base mismatch.A novel method for the ultra specific and sensitive detection of DNA in biological samples was described in this paper based on magnetic beads (MBs)-based rolling circle amplification combined with gold nano-particles (AuNPs)-aptamer labeling technique and inductively coupled plasma mass spectrometry (ICP-MS) detection. The proposed assay has an ultra-high sensitivity and stability, excellent specificity and more robust resistibility to the complex matrix due to the utilization of MBs-based rolling circle amplification, AuNPs-aptamer labeling technique and ICP-MS detection. It can be used to determine DNA or single nucleotide polymorphisms (SNP) with an extremely low detection limit of 0.1 fM (1.0×10−16 M) and a discrimination factor for single-base mismatch of 27. The proposed assay has been successfully used to detect DNA in serum sample with a recovery of 91–106% and a relative standard deviation (RSD) <6% (n=6), suggesting that our method is sensitive and reliable. The ultra-high sensitivity and specificity, easiness of fabrication, operational convenience, short analysis time, better stability and robust resistibility to the complex matrix, make the assay a promising alternative for the detection of various DNA sequence in the clinical diagnosis.

•g-C3N4 was demonstrated to catalyze the oxidation of TMB by H2O2 to produce a blue color product.•A colorimetric method for H2O2 was achieved with a limit of detection 0.9 μM.•Using g-C3N4 and GOx, a colorimetric method for glucose was developed with a detection limit of 1.0 μM.•The visual detection of glucose in serum samples could be realized.g-C3N4 was found to possess intrinsic peroxidase-like activity, and could catalytically oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 to produce a color reaction. Using g-C3N4 peroxidase-like catalytic activity and glucose oxidase (GOx), a colorimetric method for glucose detection in serum samples has been developed. The linear range for glucose was from 5 to 100 μM (R2=0.9987) and the limit of detection was as low as 1.0 μM. The proposed method was applied to detect glucose in serum samples by the naked eyes.

•WS2 nanosheets was discovered to possess intrinsic peroxidase-like activity.•Colorimetric methods for H2O2 and glucose were developed.•A portable test kit for the visual detection of blood glucose was developed.•The visual detection of glucose in serum samples could be realized.Tungsten disulfide (WS2) nanosheets were discovered to possess intrinsic peroxidase-like activity and catalyze the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) to produce a color reaction in the presence of H2O2. Based on this finding, a colorimetric method and a portable test kit for the visual detection of blood glucose have been developed by using glucose oxidase (GOx) and WS2 nanosheets-catalyzed reactions. The linear range for glucose was ranged from 5 to 300 μM (R2=0.999) with the detection limit of 2.9 μM. The portable test kit was successfully evaluated glucose levels in serum samples from normal persons and diabetes persons by the observable color change from pale yellow to yellow–green, blue–green.

•An amplified colorimetric method for the detection of Hg2+ is proposed.•The method based on the combination of T–Hg2+–T base pairs and hybridization chain reaction.•This “turn-on” sensing system enables the high sensitive and selective detection of Hg2+.•The method's detection limit is 3 orders of magnitudes lower than the MAL defined by EPA.•In this sensing system, no labeled oligonucleotides and expensive instruments are required.An amplified colorimetric detection of Hg2+ is proposed by combining T–Hg2+–T base pairs and hybridization chain reaction (HCR). Two hairpins consisting of three-fourths and one-fourth of the horseradish peroxidase (HRP)-mimicking DNAzyme in inactive configuration are used as functional elements. In the presence of Hg2+, one of the hairpins is opened by an assistant probe with the help of T–Hg2+–T base pairs and this triggers an autonomous cross-opening of the two hairpins using the strand displacement principle, resulting in the formation of DNA nanowires consisting of numerous reunited Q-quadruplex DNAzyme units. The resulting catalytically active hemin/G-quadruplex HRP-mimicking DNAzymes catalyze the oxidation of ABTS2− by H2O2 into a green-colored cationic radical ABTS•+ for the colorimetric readout. This “turn-on” sensing system enables the high sensitive and selective detection of aqueous Hg2+ with a detection limit of 9.7 pM.

A novel controllable magnetic electrochemical biosensor for the ultra-sensitive detection of single nucleotide polymorphisms (SNPs) of trace HIV-related salivary DNA is first described here based on a home-made electrically controllable magnetic gold electrode (ECM-GE).

Non-invasive early diagnosis of oral cancer is the most effective means to reduce mortality rate from this disease. In this paper, we described a novel magnetic-controllable electrochemical RNA biosensor for the ultra sensitive and specific detection of oral cancer-related microRNA (miRNA) based on a home-made electrically magnetic-controllable gold electrode. The electrically magnetic-controllable gold electrode combined the merits of heated electrode and magnetic electrode, has notable advantage such as that the strength and direction of the magnetic field and the temperature of the electrode's surface can be easily regulated. The advantage of electrically magnetic-controllable gold electrode, as well as the utilization of “junction-probe” strategy and magnetic beads (MBs)-based enzymatic catalysis amplification, make the biosensor has ultra-high sensitivity and discrimination ability even for the detection of similar miRNAs. It can be used to detect as low as 0.22 aM (2.2×10−19 M) of oral cancer-related miRNA with a recovery of 93–108% and a RSD<6 (n=5). The high sensitivity and selectivity, as well as the easiness of fabrication, operational convenience, short analysis time, good stability and re-usability, make the biosensor a promising alternative for the early point-of-care diagnosis of oral cancer. The success of the biosensor also leads to a great potential in the development of biosensor for the early diagnosis of other diseases.Highlights► A magnetic-controllable electrochemical biosensor for the detection of miRNA was reported. ► The biosensor has ultra-high sensitivity and discrimination ability for similar miRNA. ► It can be used to detect as low as 2.2×10−19 M of oral cancer-related microRNA. ► The biosensor provides a alternative for the early point-of-care diagnosis of oral cancer.

A novel DNA biosensor, which combines the merits of micro-fluidic chips, the electrophoretic driving mode, paramagnetic beads amplification, and laser-induced fluorescence detection was developed for the rapid and sequence-specific detection of DNA in this study. The proposed DNA biosensor has much higher discrimination ability for the detection of single-base mismatch and much stronger resistibility to the complex matrixes of real samples in comparison with previous biosensors. These features, as well as its ease of fabrication (the fabrication of the sensor takes only 10 min except the fabrication of micro-fluidic chip), operation convenience, stability, better re-usability (micro-fluidic chip can be reused without any extra treatment) and short analysis time (one determination only takes 15 min), make it a promising alternative to rapid detection of DNA in clinical diagnosis. With the help of the biosensor, we successfully determined DNA, which related to oral cancer, in a saliva sample without any pre-separation or dilution with a detection limit of 4.2 × 10−11 M and a relative standard deviation (n = 5) <5 %. The success in the present biosensor served as a significant step toward the practical application of the biosensor in clinical diagnosis.

A sensitive and selective Pb2+ sensor based on GR-5 DNAzyme has been developed by a flow cytometric method.

Laver samples (Porphyra haitanensis) were collected from the coastal waters of Fujian province, south-eastern China and then the speciation characteristics of arsenic in the samples were studied in detail. These laver samples contained five arsenical species, namely arsenobetaine, monomethylarsonic acid, As(V) and two kinds of arsenic-containing ribosides (arsenosugars), with a relatively high concentration of total arsenic in the range of 28.85–63.03 μg As/g dried weight. DMAsSugarMethoxy was found to be the predominant species of arsenic in lavers, accounting for 90–98% of total arsenic. As3+ was not detected and the level of inorganic arsenic was much lower than the national tolerable average residue level (TARL), suggesting that the lavers are safe for consumption.Highlights► The characterisation of arsenic in laver (Porphyra haitanensis) was reported for the first time. ► Five different arsenical species were detected in laver. ► DMAsSugarMethoxy was found to be the predominant species of arsenic in laver. ► The speciation of arsenic in seaweeds is dependent on the seaweed’s species.

More and more efforts are endeavored in the ultra-sensitive quantification of peptides and proteins, because many important peptides and proteins are present at ultra-low levels and only the quantity of them or the changes in their abundance really reflects the status and changes of a biological system. We herein report a novel ultra-sensitive method for the simultaneous quantification of three β-casomorphins (β-CMs) based on the Eu3+ diethylenetriamine-N,N,N′,N′′,N′′-pentaacetic acid labeling and capillary electrophoresis with on-line inductively coupled plasma mass spectrometry detection (CE-ICP-MS). The europium-tagged β-CMs were effectively separated by capillary electrophoresis and were sensitively determined by inductively coupled plasma mass spectrometry. Based on the europium-tagging and CE-ICP-MS, three β-CMs were baseline separated and detected within 15 min with an extremely low detection limit of 1.79–2.13 amol (1.79–2.13 × 10−11 mol L−1 for 100 nL of sample injection) and a RSD (n = 4) < 6%. The proposed method has been successfully used to detect β-CMs in real cheese samples with a recovery of 85–103%, suggesting that our method is sensitive and reliable. The success of the present method provides a new possibility for biological assays and clinical diagnoses and a new potential for simultaneous detection of low-abundant proteins or multiple biomarkers.

In this work, a reflux injection mode for the cross form micro-fluidic chip was studied. This injection mode could flexibly control the length of sample plug from less than one channel width (<83 μm) to tens of channel widths (millimeter-sized) by adjusting the injection time. Namely, the separation resolution or sample detection sensitivity could be selectively improved by changing injection time. Composed of four steps, the reflux injection mode alleviated the electrophoretic sampling bias and prevented sample leakage successfully. On a micro-fluidic chip coupled with laser induced fluorescence (LIF) detector, the injection mode was applied to separate seven oligopeptides, namely GG, GL, RPP, KPV, VKK, WYD and YWS. All analytes were completely separated and detected within 12 min with detection limits of 25–625 nmol/L. At last, the proposed method had been successfully applied to detect oligopeptides consumed by bacillus licheniformis in anode chamber of microbial fuel cell (MFC) to study the effect of oligopeptides on the MFC running.Highlights► A reflux injection mode was developed for the cross form micro-fluidic chip. ►The injection mode can control the length of sample plug from one to ten channel widths. ► The injection mode overcome electrophoretic bias and prevented sample leakage successfully. ► Seven oligopeptides were separated and determined by microchip with reflux injection mode.

A environment-friendly microwave-assisted extraction used to extract trace mercury compounds from fish samples, and a ultra-sensitive method for the analysis of Hg(II), methylmercury (MeHg) and ethylmercury (EtHg) by using capillary electrophoresis–inductively coupled plasma mass spectrometry (CE–ICP–MS) were described in this study. The extraction method is environment-friendly, simple, effective, and can be used to extract trace mercury compounds in fish samples with a satisfied recovery within several minutes. The CE–ICP–MS analytical method has a detection limit as lower as 0.021–0.032 ng Hg/mL for MeHg, EtHg and Hg(II), and can be used to determined ultratrace MeHg, EtHg and Hg(II) in natural water and fish samples directly without any preconcentration. With the help of the above methods, we have successfully determined MeHg, EtHg and Hg(II) in dried fish (Tapertail anchovy) muscle and natural water within 25 min with a RSD (relative standard deviation, n = 6) <5% and a recovery of 94–103%. Our results showed that dried muscle of T. anchovy contained only one species of mercury, MeHg, indicating that MeHg is easier to be accumulated by aquatic organisms.Highlights► A environment-friendly extraction was developed to extract trace mercury in fish. ► A sensitive method for analysis of Hg(II), MeHg and EtHg by CE–ICP–MS was reported. ► The method has a detection limit of 0.021–0.032 ng Hg/mL for MeHg, EtHg and Hg(II). ► MeHg, EtHg and Hg(II) in fish can be directly detected without any preconcentration.

We here report a novel fluorescent method for the detection of melamine based on the high fluorescence quenching ability of gold nanoparticles. The fluorescence was significantly quenched viafluorescence resonance energy transfer when fluorescein molecules were attached to the surface of gold nanoparticles by electrostatic interaction. Upon addition of melamine, the fluorescence was enhanced due to the competitive adsorption of gold nanoparticles between melamine and fluorescein. Under the optimum conditions, the fluorescence enhancement efficiency [(I − I0)/I0] showed a linear relationship with the concentration of melamine in the range of 1.0 × 10−7 mol L−1∼4.0 × 10−6 mol L−1, and the detection limit was calculated to be 1.0 × 10−9 mol L−1. The proposed method showed several advantages such as high sensitivity, short analysis time, low cost and ease of operation.

A Tb3+-promoted G-quadruplex-hemin DNAzyme was first reported in here. We demonstrated that trace Tb3+ is able to induce guanine-rich DNA (5′-TGGGTAGGGCGGGTTGGGAAA-3′) folding into a compact antiparallel G-quadruplex structure and thus allows the formation of G-quadruplex-hemin DNAzyme. The proposed DNAzyme can effectively catalyze the H2O2-mediated oxidation of TMB (3,3′,5,5′-tetramethylbenzidine sulfate) and leads to a change from colorless to blue in solution color, which provides a sensing platform for the label-free visual detection of Tb3+. Using above sensing platform, a selective and sensitive label-free visual method for the detection of trace Tb3+ was developed. The proposed method can be used to detect as low as 1.13 × 10−7 M of Tb3+ by the naked eyes observation and 9.0 × 10−9 M of Tb3+ by UV–vis spectrophotometry with a better stability and reproducibility. Compared with K+-promoted G-quadruplex-hemin DNAzyme reported in previous study, the novel Tb3+-promoted G-quadruplex-hemin DNAzyme has much higher peroxidase activity and better specificity, which lead to a great potential in the development of optical, electrochemical and chemiluminescence DNAzyme-based biosensors.

An enzyme-assisted extraction used to extract all species of selenium in rice sample and a sensitive analytical method for the determination of ultratrace Se(VI), Se(IV), SeCys2 (selenocystine) and SeMet (selenomethionine) with capillary electrophoresis-inductively coupled plasma mass spectrometry were firstly described in this study. The extraction method is simple, effective and can be used to extract trace selenium compounds in rice with high extraction efficiency and no altering its species. The analytical method has a detection limit of 0.1–0.9 ng Se/mL, and can be used to determine trace Se(VI), Se(IV), SeCys2 and SeMet in rice directly without any derivatization and pre-concentration. With the help of above methods, we have successfully determined Se(VI), Se(IV), SeCys2 and SeMet in selenium-enriched rice within 18 min with a recovery of 90–103% and a RSD (relative standard deviation, n = 6) of 3–7%. Our results indicated that selenium-enriched rice contained only one species of selenium, SeMet, and its concentration is in range of 0.136–0.143 μg Se/g dried weight. The proposed method providing a realistic approach for the nutritional and toxical evaluation of different selenium compounds in nutritional supplements.

A novel electrochemical biosensor for the genotyping/detection of single-nucleotide polymorphisms (SNPs) of trace oral-cancer salivary DNA based on junction probes containing 2′-deoxyinosine (dI) residues is described.

A simple, rapid, field-portable colorimetric method for the detection of melamine based on melamine-induced color change of label-free gold nanoparticles (Au NPs) was developed in this study. Melamine can induced the aggregation of Au NPs and results in the color change from wine-red to purple, which provided a platform for rapid and field-portable colorimetric detection of melamine. The proposed method can be used to detect melamine in liquid milk and infant formula with a detection limit of 1.0 and 4.2 ppm, respectively, within 30 min by naked eyes observation without the aid of any advanced instrument and the need of any complex pretreatment, and detect as low as 0.15 ppm of melamine in liquid milk and 2.5 ppm of melamine in infant formula with UV–vis-spectroscopy. The proposed method is promising for on-site screening of melamine adulterant in milk products.

A capillary zone electrophoresis-ultraviolet detection (CZE-UV) method for the analysis of five arsenic compounds, namely As(III), dimethylarsinic acid (DMA), p-aminophenyl arsenic acid (p-As), monomethylarsonic acid (MMA), and As(V), in sea foods was described. The optimum conditions of CE determination including detection wavelength, chemical component of buffer solution, pH value, buffer concentration, separation voltages, and injection times were studied in detail. The results indicated that the five species of arsenic were base line separated within 11 min under the optimum conditions. The relative standard deviation (RSD) of migration times was 0.50%–1.51%, and the RSD of peak areas was 1.65%–3.36%, and the detection limits were in the range of 0.004–0.30 mg l−1. The method was successfully used to determine different species of arsenic in dried shrimps with the recoveries of 93%–106%.

A new electrochemical biosensor for the monitoring of ultratrace terbium based on the conformational change of DNA containing a single guanine (G)-rich stretch was described here. The biosensor was fabricated by immobilizing a thiolated DNA containing a single G-rich stretch on the gold surface as probe surface. The G-rich DNA probe was found to be capable of changing its configuration from flexible single-stranded structures to rigid tetramolecular G-quadruplex in the presence of terbium III, which provided a switchable charge transport path for the oxidation of [Fe(CN)6]4−. The switchable surface provided a sensing platform for the single-step and reagentless detection of Tb3+. Using this reusable electrochemical sensing platform, a simple, rapid, and selective biosensor for the determination of ultratrace terbium ions with a detection limit of 6.0 × 10−11 M has been developed. The success in the present biosensor served as a significant step toward the development of monitoring ultratrace Tb3+ in river water or seawater.

A novel junction-probe electrochemical biosensor for the sequence-specific detection of DNA with higher sensitivity and higher discrimination ability was described in here. This DNA biosensor is based on “junction-probe” detection strategy, which operates via a concept called template-enhanced hybridization processes (TeHyP). TeHyP encompasses a design strategy whereby two probes that do not hybridize to each other at a specific temperature can be made to anneal to each other in the presence of a template (target) via the formation of a ternary complex (“Y” junction structure). The resulting structure that forms after the template-enhanced hybridization then was detected by electrochemical method with [Ru(NH3)6]3+ as signal molecule. We demonstrated that the formation of “Y” junction structure brings more [Ru(NH3)6]3+ to the electrode surface via electrostatic interaction and results in an increasing electrochemical signal. The increasing electrochemical signal sensitively reflects the concentration of target DNA and shows a good linear relationship with the concentration of target DNA. By employing above strategy, this DNA biosensor could detect as low as 7.6 × 10−13 M target DNA and exhibited high discrimination ability even against single-base mismatch. In addition, this novel DNA biosensor is easy to fabricate and convenient to operate, and shows good stability, reproducibility and reusability.

An improved sheath-flow interface used to couple capillary electrophoresis (CE) with inductively coupled plasma mass spectrometry (ICP-MS) and a microwave-assisted extraction used to extract each arsenic species in seafood were developed in this work. The improved sheath-flow interface completely avoids laminar flow in CE capillary caused by the suction from ICP-MS, makes electric supply more stable in CE, and transports analyte solution to ICP-MS easily and more efficiently. CE-ICP-MS coupled with our interface have two quantitative analysis modes: continuous sample-introduction mode and collective sample-introduction mode. The collective sample-introduction technique greatly reduced the dead volume of interface to approximately zero, obviously avoided the excessive dilution of analyte, and eventually led to a much lower detection limit and a much better electrophoretic resolution. This was demonstrated by the better symmetry and narrow peak widths (10–12 s) and much lower detection limits (0.030–0.042 μg/L) of four species of arsenic determined with collective sample-introduction mode.With the help of this improved sheath-flow interface and the microwave-assisted extraction, we have successfully separated and determined four arsenic species, As(III), As(V), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in dried Mya arenaria Linnaeus and Shrimp samples using CE-ICP-MS within 10 min with a relative standard deviation of 2–4% (peak areas, n = 6) and a recovery of 96–105%.

The mass concentration and size distribution of aerosols in Tokaimura were investigated using a high-volume and a low-volume Andersen sampler. A difference was found using the two samplers: the concentration of total aerosols determined with the high-volume sampler is smaller than that of the low-volume sampler by 70–90% throughout the year. Compared to the high-volume sampler, low-volume sampler gave lower concentration for aerosols >7 μm, higher concentration for aerosols of 3.3–7.0 μm and <1.1 μm, though similar results for aerosols of 1.1–3.3 μm. The low-volume sampler was found to have better separation efficiency and higher accuracy.

In order to obtain the exact chemical structure and further discuss the global warming effect of elemental carbon (EC) particles, the morphology and the chemical structure of EC particles emitted from diesel vehicles were first investigated in detail using scan electron microscopy equipped with an energy dispersive X-ray spectrometer (SEM-EDX), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), Fourier Transformation Infrared (FT-IR) spectrum and 13C Nuclear Magnetic Resonance (NMR) spectrum in this study. The SEM-EDX results showed that EC particles emitted from diesel bus are 50 nm spherical particles with smooth surface and an O/C ratio (mass ratio) of 0.07±0.01. The 50 nm EC particles were further deduced to be an aggregate of new fullerene C36(OH)2 according to the results of MALDI-TOF-MS, FT-IR and 13C NMR. Fullerenes smaller than 60C were considered to be unstable since they cannot fulfill the so-called isolated pentagon rule. So far, most of our knowledge regarding small fullerenes comes from gas-phase experiments and theoretical investigations, the production and separation of small fullerene solids in the macroscopic quantity has been reported. The present report is the first discovery of C36(OH)2-based solid.Highlights► Morphology and chemical structure of nanometer-sized EC particles were studied. ► Nanometer-sized EC particle emitted from diesel bus was found to be 50 nm ball. ► Structure of the 50 nm EC particle was studied by MALDI-TOF-MS, FT-IR and 13C NMR. ► The 50 nm EC particle was further deduced to be an aggregate of new fullerene C36(OH)2. ► Present report is the first discovery of C36(OH)2-based solid.

•A visual biosensor for sensitive and specific detection of trace UO22+ in seafood was developed.•All detecting procedures of the biosensor were carried out at room temperature.•The biosensor can be used to detect as low as 2.5 ppb UO22+ in seafood by naked-eye observation.•1000-folds of other environmentally relevant metal ions do not interfere with the detection of UO22+.A novel colorimetric biosensor, which employs DNAzyme-functionalized magnetic beads (MBs) as recognition probe, enzyme-assisted catalytic oxidation of TMB (3,3′,5,5’-tetramethylbenzidine sulfate) as signal and DNA hybridization chain reaction as amplification strategy, has been developed for detecting trace uranyl ion (UO22+) in seafood and aqueous environment with high sensitivity and specificity. We demonstrated that UO22+ can specifically cleave DNAzyme immobilized on MBs surface to release a short single-strand DNA (primer), and the released primer trigger DNA hybridization chain reaction to form a long one dimensional DNA concatamer on the MBs surface. The resulting long DNA concatamer could capture a large amount of HRP to generate the one UO22+-to-multiple HRP amplification effect. Upon the addition of TMB-H2O2 solution, the HRP-tagged DNA concatamer-MBs conjugates could catalyze the H2O2-mediated oxidation of TMB, and thus results in a color change from colorless to blue in solution. This provided a sensitive and selective sensing platform for the visual or colorimetric detection of UO22+. The proposed biosensor has high sensitivity and strong anti-interference capability, it can be used to detect as low as 2.5 ppb (9.25 nM) of UO22+ by naked-eye observation and 0.09 ppb (0.33 nM) of UO22+ by UV-visible spectrometry with no interference of other ions and a RSD ≤ 6% (n = 5). With the help of this method, we have successfully determined trace UO22+ in fish muscle and river water with a recovery of 93–106%. High sensitivity and specificity, as well operation convenience, low cost and strong resistibility to the matrix, which makes our method a potential approach for the on-site detection of UO22+ in seafood and aqueous environment.

We herein reported on novel phosphatidylserine-functionalized Fe3O4@SiO2 NPs (nanoparticles) and enzyme-encapsulated liposomes for the visual detection of Cu2+ by employing phosphatidylserine for Cu2+ recognition and the enzymatic catalysis/oxidation of 3,3′,5,5′-tetramethylbenzidine sulfate (TMB) as a signal generator. Phosphatidylserine (1,2-dioleoyl-sn-glycero-3-phospho-L-serine, DOPS) was covalently assembled on the Fe3O4@SiO2 NP surface to obtain DOPS-functionalized Fe3O4@SiO2 NPs, and was used to encapsulate horseradish peroxidase (HRP) to form HRP-encapsulated DOPS liposomes. It was demonstrated that DOPS-functionalized Fe3O4@SiO2 NPs can specifically bind HRP-encapsulated DOPS liposomes in the presence of Cu2+ at basic pH. The HRP-encapsulated DOPS liposome bound on the DOPS-functionalized Fe3O4@SiO2 NPs was then separated from solution with a magnet. Upon the addition of TMB–H2O2 solution, the HRP-encapsulated DOPS liposome bound on the DOPS-functionalized Fe3O4@SiO2 NPs was broken to release HRP, and the released HRP catalyzes the H2O2-mediated oxidation of TMB, which gives rise to a change from colourless to blue in solution colour and a new absorption peak at 652 nm. This provided a sensing platform for the sensitive, specific and field-portable colorimetric detection of Cu2+. By using the sensing platform, a selective and sensitive visual sensor for the detection of Cu2+ was developed. The proposed method has outstanding advantages including adequate sensitivity (the sensitivity can be improved by using a greater volume of the water sample), shorter analysis time, relatively low cost, operation at room temperature and stronger resistibility to the matrix. It can be used to detect as little as 0.1–0.5 μM of Cu2+ in river water using naked-eye observation and 0.05 μM of Cu2+ in river water using UV-visible spectrophotometry when 2 mL of the water sample was used for detection, within 15 min and with a recovery of 95–101% and a RSD < 5% (n = 5). A visual detection limit of 0.1–0.5 μM is much lower than the maximum allowable level of Cu2+ (∼20 μM) in drinking water defined by the USA EPA. The above features make our sensor a promising approach for the rapid and on-site detection of trace free copper ions in aqueous environments by only naked-eye observation.

A sensitive and selective Pb2+ sensor based on GR-5 DNAzyme has been developed by a flow cytometric method.

More and more efforts are endeavored in the ultra-sensitive quantification of peptides and proteins, because many important peptides and proteins are present at ultra-low levels and only the quantity of them or the changes in their abundance really reflects the status and changes of a biological system. We herein report a novel ultra-sensitive method for the simultaneous quantification of three β-casomorphins (β-CMs) based on the Eu3+ diethylenetriamine-N,N,N′,N′′,N′′-pentaacetic acid labeling and capillary electrophoresis with on-line inductively coupled plasma mass spectrometry detection (CE-ICP-MS). The europium-tagged β-CMs were effectively separated by capillary electrophoresis and were sensitively determined by inductively coupled plasma mass spectrometry. Based on the europium-tagging and CE-ICP-MS, three β-CMs were baseline separated and detected within 15 min with an extremely low detection limit of 1.79–2.13 amol (1.79–2.13 × 10−11 mol L−1 for 100 nL of sample injection) and a RSD (n = 4) < 6%. The proposed method has been successfully used to detect β-CMs in real cheese samples with a recovery of 85–103%, suggesting that our method is sensitive and reliable. The success of the present method provides a new possibility for biological assays and clinical diagnoses and a new potential for simultaneous detection of low-abundant proteins or multiple biomarkers.

A novel electrochemical biosensor for the genotyping/detection of single-nucleotide polymorphisms (SNPs) of trace oral-cancer salivary DNA based on junction probes containing 2′-deoxyinosine (dI) residues is described.

Early diagnostic methods are the most effective way to increase the survival rate of cancer patients. In this study, we present a novel method for sensitively and specifically counting cancer cells using a magnetic bead (MB)-based AuNP–aptamer labelling technique and inductively coupled plasma mass spectrometry (ICP-MS) detection. A MB-based AuNP–aptamer labelling technique can specifically recognize cancer cells and tag AuNPs to the cancer cells, which provides a platform for indirectly counting cancer cells via the detection of Au with ICP-MS. The method reported in this study combines the merits of a MB-based AuNP–aptamer labelling technique and ICP-MS detection, resulting in better specificity and stability, high sensitivity, short analysis time, and robust resistance to a complicated matrix. Especially, the employment of ICP-MS detection and the presence of MBs that facilitate the magnetic separation of target cells, not only greatly shorten the analysis time but also greatly enhance the resistance of our method to a complicated matrix. The proposed method can be used to count as few as 100 human hepatocellular carcinoma SMMC-7721 cells in 1 mL of serum with a recovery of 93–104% and a RSD < 4% (n = 5) within 3 hours. The success of this study provides a promising rapid approach for the early detection of human hepatocellular carcinoma cells in clinical diagnosis.

A novel controllable magnetic electrochemical biosensor for the ultra-sensitive detection of single nucleotide polymorphisms (SNPs) of trace HIV-related salivary DNA is first described here based on a home-made electrically controllable magnetic gold electrode (ECM-GE).

In this paper, we have reported on novel phosphatidylserine-functionalized AuNPs (gold nanoparticles) for the visual detection of Cu2+ by employing phosphatidylserine for Cu2+ recognition and AuNPs for signal generation. The phosphatidylserine (1,2-dioleoyl-sn-glycero-3-phospho-L-serine, DOPS) was covalently assembled on the AuNP surface to obtain DOPS-functionalized AuNPs. It was demonstrated that DOPS-functionalized AuNPs could specifically bind Cu2+ and lead to the aggregation of AuNPs, which gave rise to a colour change from wine-red to blue and a new absorption band around 650 nm. This provides a sensing platform for the simple, rapid and field portable colorimetric detection of Cu2+. By using the sensing platform, a selective and sensitive visual biosensor for the detection of Cu2+ was developed. The proposed biosensor has outstanding analytical advantages such as good stability, relatively high sensitivity, low cost and short analysis time. It can be used to detect concentrations of Cu2+ as low as 30 μM in river water by observation with the naked eye and of 1.55 μM Cu2+ in river water by UV-visible spectrophotometry, within 10 min and with a recovery of 98–103% and a relative standard deviation (RSD) < 4% (n = 6). The proposed biosensor is promising for on-site detection of trace Cu2+ in clinical diagnosis or environmental monitoring.