Ultrasensitive Photoelectrochemical Immunoassay Research Articles

Bio-inspired MOF nanozyme-engineered biocatalytic precipitation strategy mediates electron transfer for ultrasensitive photoelectrochemical immunoassay

Enzyme-like nanomaterials (nanozyme) has been used to generate amplified response signals in biosensors instead of the bio-enzyme, on account of their higher stability and comparable catalytical activity. Especially the metal-organic framework (MOF) materials with ultra-high porosity and high specific surface area, which is more suitable for deriving superior nanozyme. In order to deal with the increasing demand of healthcare diagnostics and biomedical research, here we proposed a novel approach for ultrasensitive photoelectrochemical (PEC) immunoassay. The bio-inspired MOF-derived nanozyme Hemin/BSA@ZIF-8 was introduced into the target biorecognition and sensing processes to accelerate the oxidization of substrate to produce insoluble precipitate, which impeded the electron transfer and led to a significant reduction in photocurrent. The proposed PEC sensor exhibited a wide linear range of 0.1 pg mL−1 ∼ 100 ng mL−1, and a low detection limit of 11.9 fg mL−1 for cardiac troponin I (cTnI) detection. This work brings a new insight of the bio-inspired MOF nanozyme-mediated PEC immunoassay designing, and offers a novel sensing strategy for accurate human biomarker analysis.

Ultrasensitive photoelectrochemical immunoassay for prostate-specific antigen based on silver nanoparticle-triggered ion-exchange reaction with ZnO/CdS nanorods.

Prostate-specific antigen (PSA), a glycoprotein that is most likely to cause prostate cancer, has attracted widespread attention in recent years due to its increasing threat to people's lives and health. Herein, we developed a new signal-amplified photoelectrochemical (PEC) immunosensing method for quantitative monitoring of the target PSA based on the ion-exchange reaction for the in situ formation of ZnO/CdS/Ag2S nanohybrids triggered by the as-released silver ions (Ag+) from silver nanolabels. Initially, the introduction of a target PSA caused the formation of a sandwich immunocomplex in an anti-PSA capture antibody (cAb)-coated microplate with the help of a silver nanoparticle-labeled detection antibody (AgNPs-dAb). Thereafter, the introduced AgNPs were dissolved with acid to release numerous silver ions. In this regard, an ion-exchange reaction occurred between the silver ions and ZnO/CdS nanorods on the photosensitive electrode, thus producing ZnO/CdS/Ag2S nanohybrids to generate a relatively strong photocurrent. Under optimal conditions, the ion-exchange reaction-based PEC immunoassay exhibited a good linear range of 0.05-50 ng mL-1 and allowed the detection of the target PSA at a concentration as low as 0.018 ng mL-1. In addition, the PEC immunoassay displayed satisfactory repeatability, high specificity, and acceptable method accuracy. Importantly, the ion-exchange reaction-based PEC immunoassay provides a new perspective for the detection of other disease-related biomarkers by controlling the corresponding antibodies.

High-activity Fe3O4 nanozyme as signal amplifier: A simple, low-cost but efficient strategy for ultrasensitive photoelectrochemical immunoassay

Sensitive but with simple, inexpensive detection of disease-related biomarkers in real biological samples is of quite necessity for early diagnosis and disease surveillance. We herein first introduced high-activity Fe3O4 nanozyme as signal amplifier to develop an ultrasensitive photoelectrochemical (PEC) immunoassay, which meanwhile has the distinct merits of both simplicity and low cost compared with previously reported enzyme-labeling PEC immunoassays. In the proposal, to illustrate and describe the PEC platform, prostate-specific antigen (PSA, Ag) was used as a target model. Specifically, ZnO nanorods (ZnO-NRs) grown vertically on a bare indium–tin oxide (ITO) electrode was deposited with ZnIn2S4 nanocrystals, producing ZnIn2S4/ZnO-NRs/ITO photoelectrode as the PEC matrix to modify capture PSA antibody (Ab1). Histidine-modified Fe3O4 (his-Fe3O4) nanozyme as signal amplifier was linked with signal PSA antibody (Ab2) to form his-Fe3O4@Ab2 conjugate, and was anchored through specific sandwich immunoreaction. The labeling his-Fe3O4 nanozyme acted as a peroxidase to induce the generation of the insoluble and insulating precipitation, resulting in an evident decrease in the photocurrent signal. On account of combined effects of high catalytic efficiency of the his-Fe3O4 nanozyme and excellent PEC properties of the ZnIn2S4/ZnO-NRs/ITO photoelectrode, ultralow detection limit of 18 fg/mL for target Ag detection was achieved. Besides, as high-activity his-Fe3O4 nanozyme has substituted natural enzyme as signal amplifier, simplicity and low cost of the PEC immunoassay was realized.

Ultrasensitive photoelectrochemical immunoassay based on CdS@Cu2O co-sensitized porous ZnO nanosheets and promoted by multiwalled carbon nanotubes

An ultrasensitive photoelectrochemical (PEC) immunosensor for the detection of carcinoembryonic antigen (CEA) was constructed using CdS@Cu2O co-sensitized porous ZnO nanosheets as photoactive materials and multiwalled carbon nanotubes (MWCNTs) as electrons sink. Porous ZnO was assembled on the MWCNTs modified indium tin oxides electrode to immobilize capture antibodies. With a sandwich immunoassay format, CEA and signal antibodies labeled CdS@Cu2O were introduced in sequence via specific immunoreaction, and the ultrahigh sensitivity of this immunoassay results from the following three aspects. First, the co-sensitization of Cu2O and CdS extends the absorption range of ZnO from ultraviolet region to visible light region, which can adequately utilize the light energy. Second, the effective matching of energy levels between the ZnO, CdS and Cu2O accelerates the separation and transfer of photogenerated electron-hole pairs and improves the PEC performance, significantly. Finally, the introduced MWCNTs evidently expedite the interfacial electron transfer from ZnO to electrode, further resulting in noticeably increased photocurrent. On the basis of multiple signal amplification strategy, a largely increased linear detection range from 1.0pgmL−1 to 80ngmL−1 with a low detection limit (0.4pgmL−1) are obtained. Meanwhile, the prepared materials with attractive properties provide a promising platform for PEC detection.

Ultrasensitive photoelectrochemical immunoassay for CA19-9 detection based on CdSe@ZnS quantum dots sensitized TiO2NWs/Au hybrid structure amplified by quenching effect of Ab2@V(2+) conjugates.

A novel, enhanced photoelectrochemical immunoassay was established for sensitive and specific detection of carbohydrate antigen 19-9 (CA19-9, Ag). In this protocol, TiO2 nanowires (TiO2NWs) were first decorated with Au nanoparticles to form TiO2NWs/Au hybrid structure, and then coated with CdSe@ZnS quantum dots (QDs) via the layer-by-layer method, producing TiO2NWs/Au/CdSe@ZnS sensitized structure, which was employed as the photoelectrochemical matrix to immobilize capture CA19-9 antibodies (Ab1); whereas, bipyridinium (V(2+)) molecules were labeled on signal CA19-9 antibodies (Ab2) to form Ab2@V(2+) conjugates, which were used as signal amplification elements. The TiO2NWs/Au/CdSe@ZnS sensitized structure could adequately absorb light energy and dramatically depress electron-hole recombination, resulting in evidently enhanced photocurrent intensity of the immunosensing electrode. While target Ag were detected, the Ab2@V(2+) conjugates could significantly decrease the photocurrent detection signal because of strong electron-withdrawing property of V(2+) coupled with evident steric hindrance of Ab2. Thanks to synergy effect of TiO2NWs/Au/CdSe@ZnS sensitized structure and quenching effect of Ab2@V(2+) conjugates, the well-established photoelectrochemical immunoassay exhibited a low detection limit of 0.0039 U/mL with a wide linear range from 0.01 U/mL to 200 U/mL for target Ag detection. This proposed photoelectrochemical protocol also showed good reproducibility, specificity and stability, and might be applied to detect other important biomarkers.

Ultrasensitive photoelectrochemical immunoassay through tag induced exciton trapping

The development of photoelectrochemical (PEC) sensors with novel principles is of significance in realizing sensitive and low-cost detection. This work uses CuO NPs labeled antibody to construct a simple and sensitive sandwich-type immunobiosensor for the detection of protein. The detection signal is produced by dissolving the CuO NPs to release copper ions, which are then added on a quantum dots (QDs) modified F-doped tin oxide to quench the photocurrent of QDs via copper ion-induced formation of exciton trapping. The formed exciton trapping blocks the escape of photoelectron and thus leads to a “signal off” PEC method for sensitive immunoassay. The proposed method shows a detectable range from 0.05 to 500ng/mL for α-fetoprotein (AFP) with a detection limit (LOD) of 0.038ng/mL. This work further extends the application of exciton trapping-based PEC biosensing strategy in bioanalysis. The sensitive analytical performance of the designed route implies a promising potential of the PEC sensing in clinical diagnosis.

Ultrasensitive photoelectrochemical immunoassay of antibody against tumor-associated carbohydrate antigen amplified by functionalized graphene derivates and enzymatic biocatalytic precipitation

Tumor-associated carbohydrate antigens (TACAs) are often found on the surface of cancer cells. The determination of the carbohydrate components of glycoconjugates is challenging because of the chemical complexity of glycan chains. Through monitoring corresponding antibody, we can get a good solution for clinical diagnosis. Here breast tumor-associated carbohydrate antigens Tn were used as a model and a new photoelectrochemical biosensor for ultrasensitive detection of antibody against Tn was developed. To enhance the sensitivity, both graphene oxide and graphene were used during the construction of biosensor. Through the formation of immunocomplex and the insoluble biocatalytic precipitation (BCP) product, photocurrent intensity was decreased greatly and the antibody could be detected from 0.5 to 500pg/mL with a detection limit of 1.0×10−13g/mL. At the same time, the developed biosensor showed acceptable selectivity and could be used in the complex matrix. Compared with the traditional glycoarray method, this PEC method is more sensitive (5 orders of magnitude), and thus provides another platform to monitor the immune response to carbohydrate epitopes at different stages during differentiation, metastasis, or treatment.

Ultrasensitive photoelectrochemical immunoassay of indole-3-acetic acid based on the MPA modified CdS/RGO nanocomposites decorated ITO electrode

A novel ultrasensitive photoelectrochemical immunosensor was fabricated based on 3-mercaptopropionic acid stabilized CdS/reduced graphene oxide (MPA-CdS/RGO) nanocomposites for indole-3-acetic acid (IAA) detection. The MPA-CdS/RGO nanocomposites were synthesized by in situ solvothermal growth of triangulated pyramidal CdS nanoparticles on the RGO sheet. 3-Mercaptopropionic acid (MPA) was employed as the modifier and bridge to immobilize the antibody. The nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and UV/vis spectra. The results showed that the MPA-CdS/RGO nanocomposites revealed enhanced photocurrent response due to excellent electron transport properties of RGO and the improved assembly of CdS nanoparticles onto RGO sheet with the introduction of MPA. Based on the dependence of the photocurrent decline on the concentration of IAA, the proposed photoelectrochemical immunosensor for IAA depicted a linear range from 0.1 to 1000ng/mL with a lower detection limit (0.05ng/mL). The high sensitivity, reproducibility and specificity of the method permitted the method suitable to be used in real samples.

Dual-Signal Amplification Strategy for Ultrasensitive Photoelectrochemical Immunosensing of α-Fetoprotein

An ultrasensitive photoelectrochemical immunoassay of cancer biomarker α-fetoprotein (AFP) is proposed that uses titanium dioxide (TiO(2)) coupled with AFP-CdTe-GOx bioconjugate, which featured AFP antigen and glucose oxidase (GOx) labels linked to CdTe quantum dots (QDs) for signal amplification. The synthesized CdTe QDs yielded a homogeneous and narrow size distribution, which allowed the binding of AFP and GOx on CdTe QDs. Greatly enhanced sensitivity for AFP came from a dual signal amplification strategy. First, an effective matching of energy levels between the conduction bands of CdTe QDs and TiO(2) allowed for fast electron injection from excited CdTe QDs to TiO(2) upon irradiation, which reduced the recombination process of electron-hole pairs and prompted photoelectrochemical performance. Second, GOx enzyme could catalyze glucose to produce H(2)O(2), which acted as a sacrificial electron donor to scavenge the photogenerated holes in the valence band of CdTe QDs, further causing an enhanced photocurrent. Thus, on the basis of the dual signal amplification strategy, the competitive immunosensor based on the specific binding of anti-AFP antibodies to AFP and AFP-CdTe-GOx bioconjugates was achieved. This proposed biosensor for AFP possessed largely increased linear detection range from 0.5 pg/mL to 10 μg/mL with a detection limit of 0.13 pg/mL. The proposed amplification strategy shows high sensitivity, stability, and reproducibility and can become a promising platform for other protein detection.

A photoelectrochemical immunosensor for benzo[a]pyrene detection amplified by bifunctional gold nanoparticles

Ultrasensitive photoelectrochemical immunoassay of polycyclic aromatic hydrocarbon (PAH) is proposed using an antibody-modified nanostructured TiO(2) electrode combined with bifunctional gold nanoparticles modified with the PAH antigen and horseradish peroxidase (HRP). The HRP-catalyzed reaction prompts the electron transfer between the electrode and electrolyte causing an excellent photocatalytic performance.