The authors describe a sensing interface that is capable of selectively adsorbing gold nanopartices (AuNPs). It was applied to electrochemiluminescent (ECL) detection of microRNA (miRNA). The AuNPs are used as signal transduction probes and luminol acts as the ECL reagent. The sensing interface was generated by sequential assembly of Nafion-carbon nanotubes (CNTs) and polyvinylpyrrolidone (PVP) at a glassy carbon electrode (GCE). If only ss-DNA probes and AuNPs are present, the interaction between them leads to the formation of ss-DNA-capped AuNPs. In this case, the capped-AuNP do not assemble at the interface of the modified electrode. As a result, the ECL is weak due to the poor electroconductivity of PVP. Conversely, if ss-DNA probes bind to target miRNA, the AuNPs can’t interact with the DNA/miRNA hybrids formed because of its rigid structure. Hence, aggregated-AuNP are generated. These are concentrated in the sensing interface due to the strong interaction between AuNP and PVP assembled at the modified electrode surface via Au-N chemical bonds. The AuNP concentrated at the surface of the modified GCE electrocatalyze the oxidation of luminol which results in strong ECL. These findings were used to design a quantitative assay for trace levels of miRNA. To confirm the viability of the method, let-7a was used as a model analyte. Under the optimal conditions, the resulting calibration plot is linear in the 40 fM. to 1.0 pM concentration range with a detection limit as low as 20 fM. The method is even capable of discriminating most let-7 miRNA family members and was successfully applied to real sample assay. In our perception, the results demonstrate that this sensing interface represents a cost-effective and sensitive tool for determination of clinically relevant cancer biomarkers.

In this work, we report a new scheme to prepare a DNA nanoprobe by adsorbing oligonucleotides on the surface of electrochemiluminescence (ECL) active chitosan/Ru(bpy)32+/silica nanoparticles (CRuS NPs). Then, the characteristics of the DNA nanoprobes were also investigated by transmission electron microscopy (TEM), gel electrophoresis (GE), and zeta potential and contact angle experiments. Our results showed that, compared to the preparation schemes of previously reported nanoprobes, this new scheme is simple and general. More importantly, the proposed DNA nanoprobes also presented the features of rapidity, specificity and sensitivity for binding to target miRNA. In the initial state of the DNA nanoprobes, the DNA nanoprobes were hardly adsorbed on a Nafion/MWNT modified electrode, and only a very low ECL signal was detected from the ECL active CRuS NPs. However, while target miRNA was present in DNA nanoprobe solution, target miRNA could hybridize with DNA probes on the DNA nanoprobe surface. As a result, this reaction forced the DNA probes away from the surface of the nanoprobes. Rigid structured double stranded DNA-miRNA products and naked CRuS NPs were formed in the solution. In this case, based on the strong affinity interaction of CRuS NPs with the Nafion film, these naked CRuS NPs could effectively be pre-concentrated on the Nafion/MWNT modified electrode and produce a stronger ECL signal. Based on this ECL signal difference, this new ECL DNA nanoprobe could detect miRNA at a 0.03 pM level and was also successfully used for miRNA detection in serum samples.

•Differential adsorption ability for single-/double-stranded nucleic acid onto U-AuNP.•Selective preconcentration of U-AuNPs to mediate amperometric signal.•Amplified amperometric signal and low background current.•105 times improved sensitivity compared to colorimetric method.•Novel sensing platform with general feasibility.The common drawback of optical methods for rapid detection of nucleic acid by exploiting the differential affinity of single-/double-stranded nucleic acids for unmodified gold nanoparticles (AuNPs) is its relatively low sensitivity. In this article, on the basis of selective preconcentration of AuNPs unprotected by single-stranded DNA (ssDNA) binding, a novel electrochemical strategy for nucleic acid sequence identification assay has been developed. Through detecting the redox signal mediated by AuNPs on 1, 6-hexanedithiol blocked gold electrode, the proposed method is able to ensure substantial signal amplification and a low background current. This strategy is demonstrated for quantitative analysis of the target microRNA (let-7a) in human breast adenocarcinoma cells, and a detection limit of 16 fM is readily achieved with desirable specificity and sensitivity. These results indicate that the selective preconcentration of AuNPs for electrochemical signal readout can offer a promising platform for the detection of specific nucleic acid sequence.

In this work, polyethyleneimine (PEI) core–silica shell nanoparticles were synthesized and used for densely grafting fluorescent receptor units inside the core of these particles to result in multi-receptor units collectively sensing a target. Herein, copper ion quenching of the fluorescence intensity of a fluorescein isothiocyanate (FITC) system was selected as a model to confirm our proof-of-concept strategy. Our results showed that, compared to free FITC in solution, a 10-fold enhancement of the Stern–Volmer constant value for Cu2+ quenching of the fluorescence intensity of the grafted state of FITC in PEI core–silica shell nanoparticles was achieved. Furthermore, compared to a previous collective sensing scheme by densely grafting fluorescent receptor units on a silica nanoparticle surface, the proposed scheme, which grafted fluorescent receptor units inside a polymer nano-core, was simple, highly efficient and presented higher sensitivity.

We report on the preparation of fluorescent silica nanoparticles (SiNPs) modified with chitosan and lucigenin by using a reverse microemulsion method. The introduction of chitosan to the lucigenin doped SiNPs is shown to improve the fluorescence quantum yield. The modified SiNPs were used as fluorescent markers in an aptamer-based method for selective determination of thrombin. In this protocol, thrombin was sandwiched between streptavidin-coated magnetic beads and the fluorescent SiNPs modified with a thrombin-binding aptamer. The method was successfully applied to the determination of thrombin in human serum and showed a detection limit as low as 0.02 nM. In our perception, the protocol presented here is promising in that such SiNPs may be applied to the sensitive fluorescent detection of other analytes by changing the corresponding aptamer.

In this work, a label-free and sensitive electrogenerated chemiluminescence (ECL) aptasensing scheme for K+ was developed based on G-rich DNA aptamer and chitosan/Ru(bpy)32+/silica (CRuS) nanoparticles (NPs)-modified glass carbon electrode. This ECL aptasensing approach has benefited from the observation that the G-rich DNA aptamer at the unfolded state showed more ECL enhancing signal at CRuS NPs-modified electrode than the binding state with K+, which folds into G-quadruplex structure. As such, the decreasing ECL signals could be used to detect K+. Compared to other aptasensing K+ approaches previously reported, the proposed ECL sensing scheme is a label-free aptasensing strategy, which eliminates the labeling, separation, and immobilization steps, and behaves in a simple, low-cost way. More importantly, because the proposed ECL sensing mechanism utilizes the nanosized ECL active CRuS NPs to sense the nanoscale conformation change from the aptamer binding to target, it is specific. In addition, due to the great conformation changes of the aptamer’s G-bases on CRuS NPs and the excellent ECL enhancing effect of guanine bases to the Ru(bpy)32+ ECL reaction, a 0.3 nM detection limit for K+ was achieved with the proposed ECL method. On the basis of these advantages, the proposed ECL aptasensing method was also successfully used to detect K+ in colorectal cancer cells.

Fluorescence sensing of an analyte based on the fluorophore collective effect is a reliable, sensitive sensing approach. Many ultralow targets can be detected on the basis of the high sensitivity and signal amplification of the fluorescence sensing system. However, the complicated synthesis procedures, harsh conditions required to design and control the fluorescence molecular probes and conjugated chain length, and the higher cost of synthesis are still challenges. To address these issues, we developed a simple, rapid, and sensitive collective effect based fluorescence sensing platform. In this sensing platform, the fluorophore unit was self-assembled on the wall of the nanopores of the porous structural silica/chitosan nanoparticles (SCNPs) on the basis of the electrostatic interaction and supermolecular interaction between the fluorophores and SiO– groups and chitosan. Since these self-assembled fluorophores are close enough to communicate with each other on the basis of the space confinement effect of the pore size, many fluorophore units could interact with a single analyte and produce an amplified fluorescence sensing ability. Chloride ion, an important anion in biological fluids, and lucigenin, a typical fluorescent dye, were used as a model to confirm the proof-of-concept strategy. Our results showed that, compared to free-state lucigenin in solution, the assembled-state lucigenin in SCNPs presented an about 10-fold increase in its Stern–Volmer constant when the concentration of Cl– was lower than 10 mM, and this fluorescence nanosensor was also successfully used to sense the chloride ion in living cells.

As one of the powerful molecular recognition elements, the functional DNA probes have been successfully utilized to construct various biosensors. However, the accurate readout of the recognition event of DNA probe binding to the specific target by label-free means is still challenging. Here, a simple and label-free electrochemiluminescence (ECL) method for sensing the recognition event of DNA probe to sequence-specific DNA is developed. Oxalate is used as an ECL co-reactant and p53 tumor suppressor gene as a model of target analyte. In the ECL sensing platform, the nanochannel structural film, which contains silica-sol, chitosan and Ru(bpy)32+, is prepared by an electrochemical deposition method. Then, DNA probes are attached onto the surface of the nanochannel-based composite film electrode based on the stronger interaction between DNA probes and chitosan embedded in the ECL composite film. These nanochannels were capped by the DNA probes. As a result, the mass-transfer channel between the Ru(bpy)32+ embedded in the nanochannel-based composite film and the ECL co-reactant in the bulk solution was greatly blocked and a weak ECL signal was observed. Conversely, in the presence of target sequences, the hybridizing reaction of targets with DNA probes could result in the escape of the DNA probes from the composite film due to the rigid structure of the duplex DNA. Thus, these nanochannels were uncapped and a stronger ECL signal was detected. Our results show that this ECL method could effectively discriminate complementary from single-base mismatch DNA sequences. Under the optimal conditions, the linear range for target DNA was from 1.0 × 10−11 to 1.0 × 10−9 mol L−1 with a detect limit of 2.7 × 10−12 mol L−1. This work demonstrates that porous structures on the silica–chitosan composite film can provide a label-free and general platform to measure the change of DNA configuration.

A new closed bipolar electrode electrochemiluminescence (ECL)-based device was designed and used to investigate the ECL behaviors of luminol in this device. The results showed that while a suitable voltage was applied to the two poles of the closed bipolar electrode, both the positive charge ions and luminol-based anionic ions could be enriched on the two poles of the closed bipolar electrode, respectively. More importantly, the ECL signals, generated from the electro-oxidation of luminol on anodic pole, was found to be related to the total amount of positive charged ions on the cathodic pole of the closed bipolar electrode. Under the optimum conditions, the ECL response was linearly to the concentration of analyte in the range of 1.0 × 10−9−1.0 × 10−8 M with a detection limit of 1.1 × 10−10 M. Based on this finding, a new ECL method for sensing the solution conductance was firstly developed.Here we design a new closed bipolar electrode electrochemiluminescence (ECL)-based device. When a suitable voltage is applied to the two poles of the closed bipolar electrode, luminol anionic ions are enriched on anodic pole and the ECL signals from the electro-oxidation of luminol are related to the total amount of positive charged ions on the cathodic pole of the closed bipolar electrode. Based on this finding, a new ECL method for sensing the solution conductance is firstly developed.

Cysteine and thioglycolic acid were immobilized on gold nanoparticles via established thiolgold surface chemistry. It is found that calcium ions rapidly induce the aggregation of the functional gold nanoparticles due to the complexation of Ca(II) by immobilized cysteine. It was also found that triethanolamine enhances the effect of calcium ions by decreasing the electrostatic repulsion between the gold nanoparticles. Transmission electron microscopy, electrophoresis, zeta potential measurements and absorptiometry were used to investigate the mechanism. Under the optimum experimental condition, the cysteine/thioglycolate/triethanolamine-modified nanoparticles were highly sensitive (the detection limit being 0.3 μM) and selective towards calcium and magnesium ions, with a linear detection range between 1.0 μM and 14 μM. Based on these findings, a rapid and selective colorimetric method was developed for assaying Ca(II) ions in serum.

This paper describes a sensitive electrogenerated chemiluminescence (ECL) method for cystine determination with improved analytical characteristics based on the combination of electrochemical parallel catalytic reaction and chemiluminescence (CL) signal sensing. Cystine can be electrochemically reduced and gives a parallel catalytic wave effect in the presence of potassium persulfate. The reaction circulated on the electrode and the amount of the reduced product of the potassium persulfate was accumulated at the electrode surface. Then the reduced product of potassium persulfate reacts with fluorescein to emit a sensitive CL signal. Investigation of the characteristics of the electrochemical and chemiluminescence reactions revealed that the speed of the electrochemical reaction was much faster than that of the subsequent CL reaction, which proved the possibility of the combination of electrochemical parallel catalytic reaction with CL signal sensing. The ECL intensity is linearly related to the cystine concentration in the range from 60 nM to 8.0 μM.

Poly(luminol–aniline) nanowires composite (PLANC) was synthesized on the surface of graphite electrode by electro-oxidizing the mixture of luminol with aniline in the H2SO4 acidic medium. The properties of the nanowires composite were characterized by transmission electron microscopy, electrogenerated chemiluminescence and electrochemical impedance spectroscopy. The investigating results showed that: firstly, while the luminol alone was electro-oxidized on the surface of the graphite electrode with the proposed synthetic method, only the polyluminol film was formed on electrode surface. However, while a suitable amount of the aniline was present in the luminol solution, the PLANC could be formed on the electrode surface and this PLANC presented better ECL properties for H2O2 compared with pure polyluminol film; secondly, since the PLANC modified electrode not only provided a larger surface area for higher glucose enzyme loading but also formed the nano-structured interface on the electrode surface to improve the analytical performances of the electrogenerated chemiluminescence (ECL) biosensor for glucose, the resulting ECL biosensor presented good response to glucose and a novel ECL biosensor for glucose was proposed.

A novel space- and time-resolved photo-induced chemiluminescence (PICL) analytical method was developed based on the photocatalysis of the Co2+-doped TiO2 nanoparticles. The PICL reaction procedure under the photocatalysis of Co2+-doped TiO2 nanoparticles was investigated using cyclic voltammetry and potentiometry. Meanwhile, the effect of the electrical double layer outside the Co2+-doped TiO2 nanoparticles on the PICL was investigated by contrasting with the Co2+-doped TiO2–SiO2 core–shell nanoparticles. Significantly, the CL intensity increased apparently and the time of the CL was prolonged in the presence of procaterol hydrochloride because the mechanism of the enhanced PICL reaction may be modified. The route of the PICL was changed due to the participation of the procaterol hydrochloride enriched at the surface of the Co2+-doped TiO2–SiO2 in the PICL reaction, which prolonged the time of the CL reaction and resulted in the long-term PICL. The analytical characteristics of the proposed in-situ PICL method were investigated using the procaterol hydrochloride as the model analyte. The investigation results showed that this new PICL analytical method offered higher sensitivity to the analysis of the procaterol hydrochloride and the PICL intensity was linear with the concentration of the procaterol hydrochloride in the range from ca. 2.0 × 10−10 to 1.0 × 10−8 g mL−1.

In this paper, it was found that the multi-wall carbon nanotubes (MWNTs) could be effectively assembled on the surface of C18 based on the strong hydrophobic interaction between MWNTs and C18. It was further found that, when the MWNTs/C18 composite was doped into the carbon paste microelectrode, it offered the powerful ability not only as the solid phase extraction materials but also as the conducting pathway to accelerate the electron exchange between the analyte, which were extracted and located within the C18 microparticles, and the electrode surface. Based on those findings, isoniazid was used as the model analyte to explore the electrochemiluminescence (ECL) analytical performance of this composite. Experimental results revealed that the composite showed rapid extraction process of isoniazid due to the powerful absorption ability of C18 and rapid electrochemical desorption process due to the conducting pathway effect of MWNTs. The highly selective and sensitive ECL determination of isoniazid was also achieved at MWNTs/C18 composite modified micro-carbon-paste electrode. Under the optimal experimental conditions, the ECL intensity was linear with the concentration of isoniazid in the range of 5.0 × 10-8–9.0 × 10-6 g/mL. The detection limit was 8.0 × 10-9 g/mL. The proposed method has been successfully applied to the determination of isoniazid in the urine samples.

In the present work, a novel method for immobilization of carbon nanotubes (CNTs) on the surface of graphite electrode was proposed. We further found that superoxide ion was electrogenerated on this CNTs-modified electrode, which can react with sulfide ion combing with a weak but fast electrogenerated chemiluminescence (ECL) emission, and this weak ECL signal could be enhanced by the oxidative products of rhodamine B. In addition, the rate constant of this electrochemical reaction k0 was investigated and confirmed that the speed of electrogenerating superoxide ion was in accordance with the subsequent fast CL reaction. Thus, the fast CL reaction of superoxide ion with target brought in the possibility of high selectivity based on time-resolved, relative to other interferences. Based on these findings, an excellently selective and highly sensitive ECL method for sulfide ion was developed. Under the optimum conditions, the enhancing ECL signals were linear with the sulfide ion concentration in the range from 6.0 × 10−10 to 1.0 × 10−8 mol L−1, and a 2.0 × 10−10 mol L−1 detection limits (3σ) was achieved. In addition, the proposed method was successfully used to detect sulfide ion in environmental water samples.

In this paper, it was found that the hydrophobic ion-associated complex of the molybdophosphoric heteropoly acid with protonated butyl-rhodamine B (BRhB) could be formed and was further selectively extracted into the bulk of the paraffin oil-based carbon paste electrode (CPE). At the same time, compared with other modifiers, the benzene-modified CPE created a suitable electrochemiluminescence (ECL) reaction microenvironment for electro-oxidation BRhB to produce the stronger ECL signal when a 1.30 V electrolytic potential was applied to the CPE in the alkaline medium. Based on these findings, a selective and sensitive ECL method for indirectly detecting phosphate was developed. Under the optimum experimental conditions, the ECL intensity was linear with the concentration of phosphate in the range of 2.0 × 10−10 to 1.0 × 10−8 g mL−1. The detection limit was 8.0 × 10−11 g mL−1. The proposed method has been applied successfully to the analysis of phosphate in the water samples.

In this paper, it was found that the enhancing effect of hydrazine on the weak electrogenerated chemiluminescence (ECL) signal of the electrooxidation of luminol at a pre-anodized platinum electrode was stronger than that of hydrazine at a bare platinum electrode. Based on this finding and the combination of this finding with a flow-injection technique, a novel, sensitive and selective ECL method for hydrazine was developed. Under the optimum experimental conditions, the relative ECL intensity was linear with hydrazine concentration over the range 2.0 × 10−8–5.0 × 10−5 mol L−1, with a detection limit of 6.0 × 10−9 mol L−1.