Vanadium-doped metal-organic framework@Znln2S4 core-shell heterojunction-attenuated photoelectrochemical immunoassay.

Considering that cancer has become the second leading cause of death in humans, it is essential to develop an analytical approach that can sensitively detect tumor markers for early detection. We report an attenuated photoelectrochemical (PEC) immunoassay based on the organic-inorganic heterojunction 10MIL-88B(FeV)/ZnIn2S4 (10M88B(FeV)/ZIS) as a photoactive material for monitoring carcinoembryonic antigen (CEA). The 10M88B(FeV)/ZIS heterojunctions have excellent light-harvesting properties and high electrical conductivity, which are attributed to the advantages of both organic and inorganic semiconductors, namely, remarkable photogenerated carrier separation efficiency and long photogenerated carrier lifetime. Horseradish peroxidase (HRP) in the presence of H2O2 can catalyze 3,3'-diaminofenamide (DAB) producing brown precipitates (oxDAB), which is then loaded onto the 10M88B(FeV)/ZIS heterojunction to reduce the photocurrent and enable the quantitative detection of CEA. Under optimal conditions, the photocurrent values of the PEC biosensor are linearly related to the logarithm of the CEA concentrations, ranging from 0.01 ng mL-1 to 100 ng mL-1 with a detection limit (LOD) of 4.0 pg mL-1. Notably, the accuracy of the PEC biosensor is in agreement with that of the human CEA enzyme-linked immunosorbent assay (ELISA) kit.

Photoelectrochemical immunoassay for thyroglobulin on nanogold-functionalized BiVO4 photoanode coupling with enzymatic biocatalytic precipitation.

Methods derived from photoelectrochemical (PEC) have been constructed for immunoassays, but most involve the split-type immunoreaction modes, and thus easily cause unpredictable intermediate precision. Herein, we innovatively designed an integrated PEC immunosensing platform for the quantitative monitoring of thyroglobulin (TG) on the gold nanoparticles (AuNPs)-functionalized BiVO4 photoanode coupling with enzymatic biocatalytic precipitation (EBCP). This sensing system could simultaneously implement the immunoreaction and photocurrent measurement. Anti-TG capture antibodies were modified onto AuNPs-decorated BiVO4 photoelectrode. A sandwich-type immunoreaction was carried out in the presence of target TG using horseradish peroxidase (HRP)-conjugated anti-TG detection antibody. The carried HRP molecules catalyzed 4-chloro-1-naphthol (4-CN) to generate an insoluble benzo-4-chlorohexadienone product on the photoanode in the presence of peroxide hydrogen, thereby decreasing the photocurrent. Under optimal conditions, the PEC immunosensors gave good photocurrent responses toward target TG within the dynamic range of 0.01-10 ng mL-1 at a detection limit of 7.6 pg mL-1. Good repeatability and precision, high specificity and acceptable storage stability were acquired during the measurement. No significant differences were encountered for screening 15 human serum specimens between the developed PEC immunoassay and commercially available enzyme-linked immunosorbent assay (ELISA) method for the detection of target TG. Significantly, PEC immunosensing system offers promise for simple and cost-effective analysis of disease-related biomarkers.

In2O3/CdIn2S4 heterojunction-based photoelectrochemical immunoassay of carcinoembryonic antigen with enzymatic biocatalytic precipitation for signal amplification.

This work reported a split-type photoelectrochemical (PEC) immunoassay for the detection of carcinoembryonic antigen (CEA) based on target-induced biocatalytic precipitation (BCP) by using In2O3/CdIn2S4 heterojunctions as the photosensitizers. The synthesized In2O3/CdIn2S4 heterojunctions improved the efficiency of charge separation and shortened the electron convey path to enhance the photocurrent, thus exhibiting high conductivity and low complexation rates of photogenerated electrons and holes. In the presence of CEA, horseradish peroxidase (HRP) catalyzed 4-chloro-1-naphthol (4-CN) to produce benzo-4-chloro-hexadienone (4-CD) through H2O2. Then, 4-CD was deposited onto the surface of In2O3/CdIn2S4 to reduce the photocurrent and realized the signal amplification. The PEC immunoassay revealed an excellent photocurrent toward target CEA within a wide range of 0.01-50 ng mL-1 at a low limit of detection of 2.8 pg mL-1 under the optimum conditions. Multiple switching light excitation tests demonstrated the good reliability and stability of the fabricated PEC biosensor. The accuracy was acceptable in comparison with human CEA enzyme-linked immunosorbent assay (ELISA) kit.

Bio-bar-code-based photoelectrochemical immunoassay for sensitive detection of prostate-specific antigen using rolling circle amplification and enzymatic biocatalytic precipitation.

Methods based on photoelectrochemistry have been developed for immunoassay, but most involve in a low sensitivity and a relatively narrow detectable range. Herein a new bio-bar-code-based split-type photoelectrochemical (PEC) immunoassay was designed for sensitive detection of prostate-specific antigen (PSA), coupling rolling circle amplification (RCA) with enzymatic biocatalytic precipitation. The bio-bar-code-based immunoreaction was carried out on monoclonal anti-PSA antibody (mAb1)-coated microplate using primer DNA and polyclonal anti-PSA antibody-conjugated gold nanoparticle (pDNA-AuNP-pAb2) with a sandwich-type assay format. Accompanying the immunocomplex, the labeled primer DNA on gold nanoparticle readily triggered RCA reaction in the presence of padlock probe/dNTPs/ligase/polymerase. The RCA product with a long single-stranded DNA could cause the formation of numerous hemin/G-quadruplex-based DNAzyme concatamers. With the assistance of nicking endonuclease, DNAzyme concatamers were dissociated from gold nanoparticle, which catalyzed the precipitation of 4-chloro-1-naphthol in the presence of H2O2 onto CdS nanorods-coated electrode (as the photoanode for the generated holes). The formed insoluble precipitate inhibited the electron transfer from the solution to CdS nanorods-modified electrode by using ascorbic acid as the electron donor. Under the optimum conditions, the photocurrent of the modified electrode decreased with the increasing of PSA concentration. A detectable concentration for target PSA with this system could be achieved as low as 1.8pgmL-1. In addition, our strategy also showed good reproducibility, high specificity and accuracy matched well with commercial PSA ELISA kits for real sample analysis. These remarkable properties revealed that the developed PEC immunoassay has great potential as a useful tool for the detection of PSA in practical application.

Nanogold-functionalized g-C3N4 nanohybrids for sensitive impedimetric immunoassay of prostate-specific antigen using enzymatic biocatalytic precipitation.

This work reports on a new impedimetric immunosensing strategy for sensitive detection of prostate-specific antigen (PSA) in biological fluids. The assay was carried out on monoclonal anti-PSA capture antibody-modified glassy carbon electrode with a sandwich-type detection format. Gold nanoparticles-decorated g-C3N4 nanosheets (AuNP/g-C3N4), synthesized by the wet-chemistry method, were utilized for the labeling of polyclonal anti-PSA detection antibody and horseradish peroxidase (HRP). Upon target PSA introduction, the sandwiched immunocomplex could be formed between capture antibody and detection antibody. Followed by the AuNP/g-C3N4, the labeled HRP could catalyze 4-choloro-1-naphthol into benzo-4-chlorohexadienone. The as-generated insoluble product was coated on the electrode surface, thus increasing the Faradaic impedance of Fe(CN)6(4-/3)(-) indicator between the solution and the base electrode. Under the optimal conditions, the impedance increased with the increasing target PSA in the sample, and exhibited a wide linear range from 10pgmL(-1) and 30ngmL(-1) with a detection limit of 5.2pgmL(-1). A repeatability and intermediate precision of <14% was accomplished. The specificity and method accuracy in comparison with commercial PSA ELISA kit for analysis of human serum specimens were relatively satisfactory.

Highly sensitive impedimetric immunosensor based on single-walled carbon nanohorns as labels and bienzyme biocatalyzed precipitation as enhancer for cancer biomarker detection.

A novel sandwich-type electrochemical immunosensor based on functionalized nanomaterial labels and bienzyme (horseradish peroxidase and glucose oxidase) biocatalyzed precipitation was developed for the detection of α-fetoprotein (AFP). The enzymes linked to functionalized nanomaterials as biocatalysts could accelerate the oxidation of 4-chloro-1-naphthol (4-CN) by H2O2 to yield the insoluble product on the electrode surface; the mass loading of the precipitates on the device led to a significant enhanced signal. Cyclic voltammetry and electrochemical impedance spectroscopy techniques were used to monitor the enhanced precipitation of 4-CN that accumulated on the electrode surface and subsequent decrement in the electrode surface area by monitoring the reduction process of the Fe(CN)6(4-/3-) redox couple. Under optimal conditions, the proposed immunosensor showed a high sensitivity and a wide linear range from 0.001 to 60 ng mL(-1) with a low detection limit of 0.33 pg mL(-1). Moreover, the immunosensor exhibited good selectivity, acceptable stability and reproducibility. The amplification strategy showed good promise for clinical screening of tumor biomarkers.