Etching of Ag nanoparticles triggered bidirectional regulation for electrochemiluminescence ratiometric immunoassay.

A highly efficient ratiometric electrochemiluminescence (ECL) immunoassay was explored by bidirectionally regulating the ECL intensity of two luminophors. The immunoassay was conducted in a split-type mode consisting of an ECL detection procedure and a sandwich immunoreaction. The ECL detection was executed using a dual-disk glassy carbon electrode modified with two potential-resolved luminophors (g-C3N4-Ag and Ru-MOF-Ag nanocomposites), and the sandwich immunoreaction using glucose oxidase (GOx)-modified SiO2 nanospheres as labels was carried out in a 96-well plate. The Ag nanoparticles (NPs) acted as bifunctional units both for triggering the resonance energy transfer (RET) with g-C3N4 and for accelerating the electron transfer rate of the Ru-MOF-Ag ECL reaction. When the H2O2 catalyzed by GOx in the 96-well plate was transferred to the dual-disk glass carbon electrode, the doped Ag NPs in the two luminophors could be etched, thus destroying the RET between C3N4 and the accelerated reaction to Ru-MOF, resulting in an opposite trend in the ECL signal outputted from the dual disks. Using the ratio of the two signals for quantification, the constructed immunosensor for a model target, i.e. myoglobin, exhibited a low detection limit of 4.7 × 10-14 g/mL. The ingenious combination of ECL ratiometry, bifunctional Ag NPs, and a split-type strategy effectively reduces environmental and human errors, offering a more precise and sensitive analysis for complex samples.

In Situ Growth Reaction on Photoelectrodes of Single-Atom Fe Incorporated Bi4O5I2: A General Photoelectrochemical Immunoassay Toward Sensitive Protein Analysis.

As one of the interesting signaling mechanisms, the in situ growth reaction on a photoelectrode has proven its powerful potential in photoelectrochemical (PEC) bioanalysis. However, the specific interaction between the signaling species with the photoactive materials limits the general application of the signal mechanism. Herein, on the basis of an in situ growth reaction on a photoelectrode of single-atom-based photoactive material, a general PEC immunoassay was developed in a split-type mode consisting of the immunoreaction and PEC detection procedure. Specifically, a single-atom photoactive material that incorporates Fe atoms into layered Bi4O5I2 (Bi4O5I2-Fe SAs) was used as a photoelectrode for PEC detection. The sandwich immunoreaction was performed in a well of a 96-well plate using Ag nanoparticles (Ag NPs) as signal tracers. In the PEC detection procedure, the Ag+ converted from Ag NPs were transferred onto the surface of the Bi4O5I2-Fe SAs photoelectrode and thereafter AgI was generated on the Bi4O5I2-Fe SAs in situ to form a heterojunction through the reaction of Ag+ with Bi4O5I2-Fe SAs. The formation of heterojunction greatly promoted the electro-hole separation, boosting the photocurrent response. Exemplified by myoglobin (Myo) as the analyte, the immunosensor achieved a wide linear range from 1.0 × 10-11 to 5.0 × 10-8 g mL-1 with a detection limit of 3.5 × 10-12 g mL-1. This strategy provides a general PEC immunoassay for disease-related proteins, as well as extends the application scope of in situ growth reaction in PEC analysis.

Cu-MOFs/GOx Bifunctional Probe-Based Synergistic Signal Amplification Strategy: Toward Highly Sensitive Closed Bipolar Electrochemiluminescence Immunoassay.

A closed bipolar electrochemiluminescence (BP-ECL) platform for sensitive prostate specific antigen (PSA) detection was proposed based on a novel synergistic signal amplification strategy. Specifically, glucose oxidase-loaded Cu-based metal-organic frameworks (Cu-MOFs/GOx) as bifunctional probes were bridged on the anodic interface with the target PSA as the intermediate unit. In virtue of the large loading capacity of Cu-MOFs, a large amount of a co-reactant, i.e., H2O2 in this L-012-based ECL system and gluconic acid were generated on the anodic pole in the presence of glucose. The generated gluconic acid could effectively degrade the Cu-MOFs to release Cu2+ which greatly accelerates the formation of highly active intermediates from co-reactant H2O2, boosting the ECL intensity. As for the cathodic pole, K3Fe(CN)6 with a lower reduction potential is used to reduce the driving voltage and speed up the reaction rate, further strengthening the ECL intensity. Thanks to the synergistic signal amplification effect at both two electrode poles of the BP-ECL system, highly sensitive detection of PSA was realized with a detection limit of 5.0 × 10-14 g/mL and a wide linear range of 1.0 × 10-13-1.0 × 10-7 g/mL. The strategy provides a novel way for signal amplification in the BP-ECL biosensing field.

Bipolar Electrochemistry - A Powerful Tool for Micro/Nano-Electrochemistry.

The understanding of areas for "classical" electrochemistry (including catalysis, electrolysis and sensing) and bio-electrochemistry at the micro/nanoscale are focus on the continued performance facilitations or the exploration of new features. In the recent 20 years, a different mode for driving electrochemistry has been proposed, which is called as bipolar electrochemistry (BPE). BPE has garnered attention owing to the interesting properties: (i) its wireless nature facilitates electrochemical sensing and high throughput analysis; (ii) the gradient potential distribution on the electrodes surface is a useful tool for preparing gradient surfaces and materials. These permit BPE to be used for modification and analytical applications on a micro/nanoscale surface. This review aims to introduce the principle and classification of BPE and BPE at micro/nanoscale; sort out its applications in electrocatalysis, electrosynthesis, electrophoresis, power supply and so on; explain the confined BPE and summarize its analytical application for single entities (single cells, single particles and single molecules), and discuss finally the important direction of micro/nanoscale BPE.

Liposome-assisted chemical redox cycling strategy for advanced signal amplification: A proof-of-concept toward sensitive electrochemiluminescence immunoassay.

This work presents a novel signal amplification strategy for electrochemiluminescence (ECL) biosensor based on liposome-assisted chemical redox cycling for in situ formation of Au nanoparticles (Au NPs) on TiO2 nanotubes (TiO2 NTs) electrode. The system was exemplified by ascorbic acid (AA)-loaded liposome, the redox cycling of AA utilizing tris (2-carboxyethyl) phosphine (TCEP) as reductant, and the use of Au nanoclusters (Au NCs)/TiO2 NTs as working electrode to implement the ECL detection of prostate specific antigen (PSA). Specifically, the AA-loaded liposomes were used as tags to label the captured PSA through a sandwich immunoreaction. After the lysate of the liposome was transferred onto the interface of Au NCs/TiO2 NTs in the presence of Au3+ and TECP, the chemical redox cycling was triggered. In the cycling, Au3+ was directly reduced in situ by AA to form Au NPs on Au NCs/TiO2 NTs electrode, whereas the oxidation product of AA was reduced by TCEP to regenerate AA. The large loading capacity of the liposome and chemical redox cycling resulted in the incomplete reduction of the Au NCs to Au NPs on the TiO2 NTs electrode, enhancing the ECL intensity greatly. The multiple signal amplification strategy achieved an ultrasensitive detection for PSA with a detection limit down to 6.7 × 10-15 g mL-1 and a wide linear concentration range from 1.0 × 10-14 to 1.0 × 10-8 g mL-1. It is believed that this work is anticipated to extend the employment of advanced chemical redox cycling reaction in the field of ECL bioassays.

In Situ Formation of Bi2MoO6-Bi2S3 Heterostructure: A Proof-Of-Concept Study for Photoelectrochemical Bioassay of l-Cysteine.

A novel signal-increased photoelectrochemical (PEC) biosensor for l-cysteine (L-Cys) was proposed based on the Bi2MoO6-Bi2S3 heterostructure formed in situ on the indium-tin oxide (ITO) electrode. To fabricate the PEC biosensor, Bi2MoO6 nanoparticles were prepared by a hydrothermal method and coated on a bare ITO electrode. When L-Cys existed, Bi2S3 was formed in situ on the interface of the Bi2MoO6/ITO electrode by a chemical displacement reaction. Under the visible light irradiation, the Bi2MoO6-Bi2S3/ITO electrode exhibited evident enhancement in photocurrent response compared with the Bi2MoO6/ITO electrode, owing to the signal-increased sensing system and the excellent property of the formed Bi2MoO6-Bi2S3 heterostructure such as the widened light absorption range and efficient separation of photo-induced electron-hole pairs. Under the optimal conditions, the sensor for L-Cys detection has a linear range from 5.0 × 10-11 to 1.0 × 10-4 mol L-1 and a detection limit of 5.0 × 10-12 mol L-1. The recoveries ranging from 90.0% to 110.0% for determining L-Cys in human serum samples validated the applicability of the biosensor. This strategy not only provides a method for L-Cys detection but also broadens the application of the PEC bioanalysis based on in situ formation of photoactive materials.

H2O2-activated independently bidirectional regulation for a sensitive and accurate electrochemiluminescence ratiometric analysis.

Potential-resolved electrochemiluminescence (ECL) ratiometric analysis has become a research hotspot in bioassays by virtue of its good accuracy, versatility and specificity. Current ECL ratiometry mainly focuses on the competition for the co-reactant or quantitative analysis using a variable signal and a changeless signal; the disorganized change or small difference between the two signals may affect the accuracy and sensitivity of detection. In this study, we have developed a novel ECL ratiometric sensor based on the bidirectional regulation of two independent co-reaction systems by H2O2. H2O2 as a bidirectional moderator permits the ECL signals of the cathode and anode to independently change in opposite trends, which greatly enhances the organization and difference between the two signals. The ratio of the two signals is used to realize the quantitative analysis of myoglobin (MyO) with a good linear relationship between log(ECLcathode/ECLanode) and log CMyO in the range of 1.0 × 10-13 to 1.0 × 10-7 g mL-1. The detection limit is 4.0 × 10-14 g mL-1. Furthermore, it showed excellent performance in the determination of MyO in human serum samples. The proposed biosensor provides some developments for the sensitive and accurate detection of disease markers.

A membraneless self-powered photoelectrochemical biosensor based on Bi2S3/BiPO4 heterojunction photoanode coupling with redox cycling signal amplification strategy.

The photoelectrochemical (PEC) self-powered system has attracted great attention in disease detection. The determination of a simple and efficient approach for disease-related biomarkers is highly interesting and appealing. Herein, an ingenious visible light-induced membraneless self-powered PEC biosensing platform was constructed, integrating a signal amplification strategy for ultrasensitive split-type PEC bioanalysis. The system was comprised of a Bi2S3/BiPO4 heterojunction photoanode and a platinum (Pt) cathode in a one compartment chamber. An alkaline phosphatase (ALP)-loaded sandwich immunoassay was used to generate the signal reporter ascorbic acid (AA) in a 96-well plate, and myoglobin (Myo) was used as a model protein. In the presence of AA, ferrocene (Fc), and Tris (2-carboxyethyl) phosphine (TCEP), the chemical-chemical redox cycling scheme was operated upon the initial oxidation of Fc by the holes in the Bi2S3/BiPO4 photoelectrode, and Fc was regenerated from Fc+ by AA. Subsequently, AA was regenerated by TCEP after its oxidation, and cycling was triggered. As a result, the proposed self-powered PEC sensing exhibited excellent performance with a wide linear range from 5.0 × 10-13 to 1.0 × 10-7 g/mL, and a low detection limit of 2.0 × 10-13 g/mL for Myo. This work provided a new design of a redox cycling strategy in the self-powered PEC biosensor, and showed an effective approach for the clinical diagnosis.

Dual-wavelength electrochemiluminescence ratiometry for hydrogen sulfide detection based on Cd2+-doped g-C3N4 nanosheets.

Herein, a novel and facile dual-wavelength ratiometric electrochemiluminescence-resonance energy transfer (ECL-RET) sensor for hydrogen sulfide (H2S) detection was constructed based on the interaction between S2- and Cd2+-doped g-C3N4 nanosheets (NSs). Cd2+-doped g-C3N4 NSs exhibited a strong ECL emission at 435 nm. In the presence of H2S, CdS was formed in situ on g-C3N4 NSs by the adsorption of S2- and Cd2+, generating another ECL emission at 515 nm. Furthermore, the overlapping of the absorption spectrum of the formed CdS and the ECL emission spectrum of g-C3N4 NSs led to a feasible RET, thus quenching the ECL intensity from g-C3N4 at 435 nm. Through an ECL decrease at 435 nm and an increase at 515 nm, a dual-wavelength ratiometric ECL-RET system for H2S was designed. The sensor exhibited a lower detection limit of 0.02 µM with a wide linear range of 0.05-100.0 µM. In addition, the applicability of the method was validated by plasma sample analysis with a linear range of 80.0-106.0%. We believe that such a proposal would provide new insight into advanced dual-wavelength ECL ratiometric assays.

Photogenerated Hole-Induced Chemical-Chemical Redox Cycling Strategy on a Direct Z-Scheme Bi2S3/Bi2MoO6 Heterostructure Photoelectrode: Toward an Ultrasensitive Photoelectrochemical Immunoassay.

To achieve high sensitivity for biomolecule detection in photoelectrochemical (PEC) bioanalysis, the ideal photoelectrode and ingenious signaling mechanism play crucial roles. Herein, the feasibility of the photogenerated hole-induced chemical-chemical redox cycling amplification strategy on a Z-scheme heterostructure photoelectrode was validated, and the strategy toward enhanced multiple signal amplification for advanced PEC immunoassay application was developed. Specifically, a direct Z-scheme Bi2S3/Bi2MoO6 heterostructure was synthesized via a classic hydrothermal method and served as a photoelectrode for the signal response. Under the illumination, the PEC chemical-chemical redox cycling (PECCC) among 4-aminophenol generated by the enzymatic catalysis from a sandwich immunoassay, ferrocene as a mediator, and tris (2-carboxyethyl) phosphine as a reducing agent was run on the Z-scheme Bi2S3/Bi2MoO6 heterostructure photoelectrode. Exemplified by interleukin-6 (IL-6) as the target, the applicability of the strategy was studied in a PEC immunoassay. Thanks to the multiple signal amplification originating from the high efficiency of the PECCC redox cycling system, the enzymatic amplification, and the fine performance of the Z-scheme Bi2S3/Bi2MoO6 heterostructure photoelectrode, the assay for IL-6 exhibits a very low detection limit of 2.0 × 10-14 g/mL with a linear range from 5.0 × 10-14 to 1.0 × 10-8 g/mL. This work first validates the feasibility of the PECCC redox cycling on the Z-scheme heterostructure photoelectrode and the good performance of the strategy in PEC bioanalysis. We envision that it would provide a new prospective for highly sensitive PEC bioanalysis on the basis of a Z-scheme heterostructure.

A novel split-type photoelectrochemical immunosensor based on chemical redox cycling amplification for sensitive detection of cardiac troponin I.

Photoelectrochemical (PEC) immunoassay is a burgeoning and promising bioanalytical method. However, the practical application of PEC still exist some challenges such as the inevitable damage of biomolecules caused by the PEC system and the unsatisfactory sensitivity for biomarkers with low abundance in real sample. To solve the problems, we integrated the cosensitized structure of Ag2S/ZnO nanocomposities as photoelectrode with photogenerated hole-induced chemical redox cycling amplification (CRCA) strategy to develop a split-type PEC immunosensor for cardiac troponin I (cTnI) with high sensitivity. Initially, the immunoreaction was carried out on the 96-well plates in which alkaline phosphatase (ALP) could catalyze ascorbic acid 2-phosphate (AAP) to generate the signal-reporting species ascorbic acid (AA). Subsequently, the AA participated and the tris (2-carboxyethyl) phosphine (TCEP) mediated chemical redox cycling reaction took place on the photoelectrode, thus leading to signal amplification. Under the optimized conditions, the immunosensor demonstrated a detection limit (LOD) of 3.0 × 10-15 g mL-1 with a detection range of 1.0 × 10-14 g mL-1 to 1.0 × 10-9 g mL-1 for cTnI. Impressively, the proposed method could determine the cTnI in human serum samples with high sensitivity and satisfactory accuracy. Considering the virtues of the photoelectrode and the chemical redox cycling strategy, the method would hold great potential for highly sensitive biosensing and bioanalysis.

Liposome-assisted enzyme catalysis: toward signal amplification for sensitive split-type electrochemiluminescence immunoassay.

Developing an efficient signal amplification strategy is very important to improve the sensitivity of bioanalysis. In this paper, a liposome-assisted enzyme catalysis signal amplification strategy was developed for electrochemiluminescence (ECL) immunoassay of prostate specific antigen (PSA) in a split-type mode. The sandwich immunoreaction occurred in a 96-well plate, and glucose oxidase (GOx) encapsulated and antibody-modified liposomes were used as labels. The ECL detection was carried out using a rGO-Au NP modified glassy carbon electrode (GCE). The large amount of generated H2O2, i.e. the coreactant of the luminol system, and the excellent catalytic behavior of rGO-Au NPs greatly boosted the ECL signal, resulting in the signal amplification. The developed ECL immunosensor for detecting PSA achieved a wider linear range from 1.0 × 10-13 to 1.0 × 10-8 g mL-1 and a detection limit of 1.7 × 10-14 g mL-1. The application of the proposed strategy was demonstrated by analyzing PSA in human serum samples with recoveries from 89.0% to 113.0%, and relative standard deviations (RSDs) were less than 6.6%. This work provides a new horizon to expand the application of liposomes for ECL bioanalysis.

Chemical-chemical redox cycling amplification strategy in a self-powered photoelectrochemical system: a proof of concept for signal amplified photocathodic immunoassay.

A chemical-chemical redox cycling amplification strategy was introduced into a photocathodic immunosensing system. To prove the applicability of the method, a novel self-powered photochemical system by integrating the photoanode and photocathode was designed for protein analysis.

A novel chemiluminescence imaging immunosensor for prostate specific antigen detection based on a multiple signal amplification strategy.

A novel chemiluminescence (CL) imaging platform was constructed for prostate specific antigen (PSA) detection in a multiple signal amplifying manner. To construct the platform, the primary antibody for PSA was firstly immobilized on a O-ring area of a glass slide for recognizing the PSA. The horseradish peroxidase (HRP) and the secondary antibody of PSA (Ab2) functionalized Au NPs (HRP-Au NPs-Ab2) were modified on the platform through immunoreaction between PSA and Ab2. The excellent catalytic effect of Au NPs and HRP on the HRP-Au NPs-Ab2 to the luminol-H2O2 CL system provided the dual-signal amplification for PSA detection. To further enhance the sensitivity, tyramine signal amplification (TSA) strategy was introduced: tyramine-HRP conjugates were added into the O-ring reservoir and thus tyramine-HRP repeats formed in the presence of H2O2, generating a multiple signal amplification because of the large amounts of HRP on the sensing interface. The excellent performance of HRP-Au NPs-Ab2 and TSA strategy endows the CL platform with high sensitivity. The PSA was detected with a photomultiplier tube (PMT) and visually analyzed by a charge coupled device (CCD), respectively. The linear ranges of PMT and CCD for PSA are 0.1-100.0 ng mL-1 with a detection limit of 0.05 pg mL-1 and 0.5 - 100.0 ng mL-1 with a detection limit of 0.1 pg mL-1, respectively. The levels of PSA in several human serum samples were determined and the recoveries are ranged from 82.5% - 117.0%. This CL immunosensing platform holds great potential for bioactive molecules detection visually and sensitively.

A ternary CdS@Au-g-C3N4 heterojunction-based photoelectrochemical immunosensor for prostate specific antigen detection using graphene oxide-CuS as tags for signal amplification.

Photoactive materials with high photo-electron transfer efficiency and stable signal output hold a key role in constructing the photoelectrochemical (PEC) biosensing systems. In this study, the ternary CdS@Au-g-C3N4 heterojunction was first prepared and characterized, and its application in PEC bioanalysis was explored. The gold nanoparticles sandwiched between CdS and g-C3N4, acting as both plasmonic photosensitizer and electron relay, significantly boosted the light absorption and accelerated the charge transfer from g-C3N4 to CdS, both of which contributed to the enhancement of photoelectric conversion efficiency. Signal quenching with graphene oxide-CuS efficiently weakened the photocurrent from CdS@Au-g-C3N4. The combination of the excellent PEC properties of CdS@Au-g-C3N4 and the remarkable quenching effects of graphene oxide-CuS enabled construction of a sandwich-type PEC immunosensor for prostate specific antigen (PSA) detection. This immunosensor achieved sensitive PSA analysis by multiple signal amplification mechanisms, with a detection limit of 0.6 pg mL-1 and a wide linear range from 1.0 pg mL-1 to 10 ng mL-1. This work not only demonstrates the great potential of noble metal sandwiched ternary heterojunctions in the PEC field, but also lays a foundation for developing the general PEC immunoassays.

Recent progress of heterostructure-based photoelectrodes in photoelectrochemical biosensing: a mini review.

Photoelectrochemical (PEC) biosensing has received increasing attention due to its great potential in the analysis of biomarkers. The performance of a PEC biosensor depends largely on photosensitive materials. The photoactive materials with excellent properties are of great importance to realize advanced PEC bioassays. Recently, as a special class of nanocomposites, heterostructures consisting of different types of semiconductors with potential applications in PEC systems have witnessed the rapid development to improve the performance of PEC biosensors. In this review, the research progress on the promising heterostructures has been introduced and summarized, and the applications of such heterostructures in PEC bioassays are provided. The future development of heterostructures pertaining to PEC biosensing systems has also been briefly discussed.

A potentiometric resolved photoelectrochemical system based on CdS nanowires and SnNb2O6 nanosheets: a case application for dual biomarker analysis.

A potentiometric resolved photoelectrochemical (PEC) system based on CdS nanowires and SnNb2O6 nanosheets was developed. To prove the applicability of this system in PEC multi-biomarker analysis, a label free PEC immunosensor for two cardiac biomarkers, myoglobin and cardiac troponin I, was constructed.

Copper ion modified graphitic C3N4 nanosheets enhanced luminol-H2O2 chemiluminescence system: Toward highly selective and sensitive bioassay of H2S in human plasma.

A high-efficient chemiluminescence (CL) platform for highly selective and sensitive H2S detection was constructed on the basis of the quenching effect of S2- on the copper ion modified graphitic carbon nitride nanosheets (Cu2+-g-C3N4 NSs) enhanced luminol-H2O2 system. Cu2+-g-C3N4 NSs with horseradish peroxidase-like catalytic activity were prepared and provide a great improvement for luminol-H2O2 system. The presence of S2- induced the formation of CuS precipitate on g-C3N4 NSs surface. The precipitate can block the catalytic Cu2+ sites on the g-C3N4 NSs surface, resulting in a great CL decrease of CL system. Based on such a mechanism, a simple, highly selective and sensitive CL biosensor for H2S detection was designed. Under the optimized conditions, luminol-H2O2-Cu2+-g-C3N4 NSs system gave a decrease of CL intensity with the Na2S concentration increasing. The CL biosensor is in a linear range of 10.0 pM-50.0 nM and the detection limit for detecting Na2S is as low as 2.0 pM. Moreover, the method here has enjoyed a successful application for determining H2S in human plasma samples and the recovery is between 95.7% and 110.0%.

CdS:Mn-sensitized 2D/2D heterostructured g-C3N4-MoS2 with excellent photoelectrochemical performance for ultrasensitive immunosensing platform.

The exploration of advanced photoactive materials with fine photoelectrochemical (PEC) performance is always the hot subject in PEC bioanalysis. Herein, Mn-doped CdS nanocrystals (CdS:Mn)-sensitized 2D/2D heterostructured g-C3N4-MoS2 was prepared and served as photoactive matrix of PEC sensing platform for myoglobin (Myo) detection using CuO nanoparticles labeled anti-Myo (anti-Myo-CuO) conjugates as signal amplification tags. The heterostructured g-C3N4-MoS2 could effectively promote the electron transfer and evidently restrain the recombination of electron-hole pairs, producing the high photocurrent response. Upon loaded CdS:Mn on the heterostructured g-C3N4-MoS2 to form co-sensitized structure, the photocurrent further gives a dramatically increase. To proof the performance of the co-sensitized structure in PEC bioanalysis, a sandwich type PEC immunosensor was designed by using the co-sensitized structure as photomatrix, Myo as model protein, and anti-Myo-CuO conjugates as amplifying tags. The introduction of anti-Myo-CuO conjugates in this system could significantly quench the PEC response of the sensing interface owing to the competition of the light-generated electron, poor conductivity and steric hindrance of the anti-Myo-CuO conjugates. In virtue of synergistic amplification of the CdS:Mn sensitized heterostructured g-C3N4-MoS2 and the anti-Myo-CuO conjugates, the immunosensor could respond down to 0.42 pg mL-1 Myo with a detectable range of 1.0 pg mL-1 to 50 ng mL-1. Moreover, this PEC platform demonstrates high specificity and sensitivity for Myo detection in real biological matrices. This strategy may furnish new insights for applications of novel 2D/2D heterostructures in PEC bioanalysis.

Reduced graphene oxide-gold nanoparticles-catalase-based dual signal amplification strategy in a spatial-resolved ratiometric electrochemiluminescence immunoassay.

A novel spatial-resolved electrochemiluminescent (ECL) ratiometry for cardiac troponin I (cTnI) analysis was developed using resonance energy transfer (RET) and a coreactant consumption strategy for signal amplification. Specifically, the spatial-resolved dual-disk glassy carbon electrodes were modified with CdS nanowires (CdS NWs) and luminol-gold nanoparticles (L-Au NPs) as potential-resolved ECL emitters, respectively. After stepwise immobilization of anti-cTnI and bovine serum albumin on the dual-disk electrodes, the CdS NWs-based electrode, with varied concentrations of cTnI, was used to provide a working signal, whereas the L-Au NPs-based electrode, with a fixed amount of cTnI, was employed to provide the reference signal. To efficiently amplify the working signal on the CdS NWs-based electrode, an anti-cTnI-reduced graphene oxide-gold nanoparticles-catalase probe (anti-cTnI-rGO-Au NPs-CAT) was loaded onto the electrode to form a sandwich immunocomplex. The RET from CdS NWs to Au NPs and the coreactant (i.e. H2O2) consumption by the CAT generate a significant ECL decrease on the CdS NWs-based electrode in the presence of cTnI. This novel and sensitive ratiometric detection mode for cTnI was achieved using the ratio values of the working signal of the CdS NWs-based electrode and the reference signal of the L-Au NPs-based electrode. The integration of RET and coreactant consumption strategy in the designed spatial-resolved ratiometric platform endows the immunosensor with a wide linear range of 5.0 × 10-13 - 1.0 × 10-7 g mL-1 and a low detection limit of 0.10 pg mL-1 for cTnI. Furthermore, the method exhibits high accuracy and sensitivity for cTnI determination in human serum samples.