Immunogold labeling-induced synergy effect for amplified photoelectrochemical immunoassay of prostate-specific antigen

Design of a photoelectrochemical lab-on-a-chip immunosensor based on enzymatic production of quantum dots in situ

We present a new photoelectrochemical immunoassay based on a microfluidic device. Its operation employs enzymatic generation of CdS quantum dots.

Au nanoclusters-decorated WO3 nanorods for ultrasensitive photoelectrochemical sensing of Hg2+

Ultrasensitive photoelectrochemical sensing of Hg2+ is achieved using Au nanocluster-decorated WO3 nanorods as photoactive materials.

Polydopamine nanospheres with multiple quenching effect on TiO2/CdS:Mn for highly sensitive photoelectrochemical assay of tumor markers

A photoelectrochemical (PEC) immunosensing strategy based on the multiple quenching of polydopamine nanoparticles (PDA NPs) to Mn²⁺-doped CdS-modified TiO₂ nanoparticles (TiO₂/CdS:Mn) was designed for the highly sensitive detection of carcinoembryonic antigen (CEA). The uniform PDA NPs possessed good dispersibility, good biocompatibility, and abundant functional groups for biomolecule assembly. They also had unique photophysical properties, with light absorption spanning the visible to infrared light range. When the immune-recognition brought the PDA NPs close to the TiO₂/CdS:Mn interface, the PDA NPs competed with TiO₂/CdS:Mn to absorb light, consumed photoelectrons generated in the TiO₂/CdS:Mn, and hindered the access of electron donors to photoactive materials. The contribution from these aspects thus led to a significant decrease in photocurrent. Benefiting from the multiple quenching mechanism, the PEC immunosensor showed high sensitivity for CEA detection. Under optimal conditions, a low detection limit of 0.02 pg/mL and a wide linear relationship from 0.1 pg/mL to 100 ng/mL were obtained. The immunoassay showed good reproducibility and stability, and good selectivity and high accuracy in serum sample analysis. In this regard, PEC immunosensors may have great application potential for screening tumor markers and the prevention and monitoring of serious diseases.

Electrochemically Controlled ATRP for Cleavage-Based Electrochemical Detection of the Prostate-Specific Antigen at Femtomolar Level Concentrations

As a single-chain glycoprotein with endopeptidase activity, the prostate-specific antigen (PSA) is valuable as an informative serum marker in diagnosing, staging, and prognosis of prostate cancer. In this report, an electrochemical biosensor based on the target-induced cleavage of a specific peptide substrate (PSA peptide) is designed for the highly selective detection of PSA at the femtomolar level, using electrochemically controlled atom transfer radical polymerization (eATRP) as a method for signal amplification. The PSA peptides, without free carboxyl sites, are attached to the gold surface via the N-terminal cysteine residue. The target-induced cleavage of PSA peptides results in the generation of carboxyl sites, to which the alkyl halide initiator α-bromophenylacetic acid (BPAA) is linked via the Zr(IV) linkers. Subsequently, the potentiostatic eATRP of ferrocenylmethyl methacrylate (FcMMA, as the monomer) leads to the surface-initiated grafting of high-density ferrocenyl polymers. As a result, a large amount of Fc redox tags can be recruited for signal amplification, through which the limit of detection (LOD) for PSA can be down to 3.2 fM. As the recognition element, the PSA peptide is easy to synthesize, chemically and thermally stable, and low-cost. Without the necessity of enzyme or nanoparticle labels, the eATRP-based amplification method is easy to operate and low-cost. Results also show that the cleavage-based electrochemical PSA biosensor is highly selective and applicable to PSA detection in complex biological samples. In view of these merits, the integration of the eATRP-based amplification method into cleavage-based recognition is believed to hold great promise for the electrochemical detection of PSA in clinical applications.

An off-on electrochemiluminescence detection for microRNAs based on TiO2 nanotubes sensitized with gold nanoparticles as enhanced emitters

A sensitive electrochemiluminescence (ECL) assay for microRNAs (miRNAs) based on a semiconductor nanomaterial sensitized with noble-metal Au nanoparticles (NPs) is successfully developed. TiO₂ nanotubes (NTs) were equipped with Au NPs to obtain an enhanced ECL emitter. Then, an ECL assay for miRNA-21 was fabricated, which was based on the use of probe 2 DNA-functionalized Pt/PAMAM nanocomposites (NCs) assembled on the surface of Au/TiO₂ NT conjugate via DNA hybridization between probe 1 DNA and capture DNA. The Pt/PAMAM NCs act as an ECL quencher of Au/TiO₂ NTs via resonance energy transfer. After the binding of target miRNA-21 and the capture DNA, the Pt/PAMAM NCs were released and the ECL signal was recovered. An "off-on" ECL assay was achieved with a linear response from 0.01 to 10,000 pM. Finally, this method has been validated to be sensitive and specific for miRNAs in human serum samples. The ECL enhancement strategy opens a new way for fabricating various sensitive biosensors. Graphical abstract A sensitive "off-on" electrochemiluminescence analysis method was developed, which combined Au NP-enhanced ECL emission of TiO₂ nanotubes and an efficient energy-transfer system between Au/TiO₂ nanotubes and Pt/PAMAM nanocomposites.

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

A potentiometric-resolved PEC immunosensor was developed for dual-target detection.

An CuInS2 photocathode for the sensitive photoelectrochemical determination of microRNA-21 based on DNA-protein interaction and exonuclease III assisted target recycling amplification

A photocathode is described for the determination of microRNA-21 by using CuInS₂ as an active photocathode material. Exonuclease III assisted target recycling amplification was employed to enhance the detection sensitivity. The TATA-binding protein (TBP) was applied to enhance steric hindrance which decreases the photoelectrochemical intensity. This strategy is designed by combining the anti-interference photocathode material, enzyme assisted target recycling amplification and TBP induced signal off, showing remarkable amplification efficiency. Under the optimized conditions, the detection limit for microRNA-21 is as low as 0.47 fM, and a linear range was got from 1.0 × 10^-15 M to 1.0 × 10^-6 M. Graphical abstract Schematic representation of sensitive photoelectrochemical detection of microRNA-21.CuInS₂ is used as an active photocathode material. Combined Exonuclease III assisted target recycling amplification and TATA-binding protein decreased of photoelectrochemical intensity, the detection limit was 0.47 fM with good selectivity. (miR-21: microRNA-21; CS: chitosan).

Recent developments of photoelectrochemical biosensors for food analysis

Recent developments of photoelectrochemical biosensors for food analysis are summarized and the future prospects in this field are discussed.

A novel fluorescence immunosensor based on Förster resonance energy transfer between nitrogen and sulfur co-doped carbon dot functionalized silica nanospheres and Au@Ag NPs

A fluorescence immunosensor for PSA detection was developed based on the FRET between Si/NS-CDs and Au@Ag NPs.

A versatile cathodic "signal-on" photoelectrochemical platform based on a dual-signal amplification strategy

Novel cathodic photoelectrochemical (PEC) aptasensors for sensitive and selective determination of thrombin and Pb²⁺ were developed based on a new dual-signal amplification strategy. The presence of gold nanoparticles (AuNPs) could quench the PEC signal of bismuth oxyiodide (BiOI). At the same time, the redox moiety G-quadruplex/hemin or ferrocene (Fc) was found to enhance the PEC signal of BiOI. So, in the presence of thrombin or Pb²⁺, the interaction between target and the aptamer resulted in the releasement of the AuNPs, as well as shorter distance between the redox moiety and the electrode surface. Hence dual-enhanced cathodic PEC biosensor strategy was realized. Under the optimized conditions, the detection limits of thrombin and Pb²⁺ were 17.3 fM and 3.16 pM, respectively with good selectivity. At the same time, the PEC performance of redox moiety G-quadruplex/hemin and Fc was compared.

Reduced graphene oxide-functionalized FeOOH for signal-on photoelectrochemical sensing of prostate-specific antigen with bioresponsive controlled release system

A new and signal-on photoelectrochemical (PEC) sensing platform was successfully designed for the sensitive detection of prostate-specific antigen (PSA), using reduced graphene oxide- functionalized iron oxyhydroxide (FeOOH-rGO) as the photoactive material, accompanying target-responsive controlled release system to achieve the signal amplification. Introduction of rGO as electron mediator greatly facilitated the electron transfer from FeOOH to electrode under visible light, which inhibited the electron-hole recombination to enhance the photo-activity of FeOOH-rGO. Additionally, the bioresponsive release system was controlled via the reaction of target PSA with the aptamer capped glucose-loading mesoporous silica nanoparticle (MSN) to release numerous glucose molecules (as the electron donors) for the amplification of the photocurrent generated from FeOOH-rGO. Thus, more glucose molecules could be released and enhanced photocurrents could be obtained with the increasing PSA concentrations. Experimental results showed that the photocurrents of the PEC sensing platform were linearly dependent on the logarithm of PSA concentrations from 1.0pg/mL to 100ng/mL. Moreover, the PEC sensing system afforded good stability and specificity, and its accuracy matched well with the commercial PSA enzyme-linked immunosorbent assay (ELISA) kit. The excellent performance of the PEC sensing platform indicated its promising prospect as a useful tool for PSA detection in practical application.

An ultrasensitive energy-transfer based photoelectrochemical protein biosensor

Using single stranded DNA (ssDNA) as a distance controller and Au nanoparticles (NPs) functionalized with ssDNA as novel energy-transfer nanoprobes, an ultrasensitive energy-transfer based photoelectrochemical protein biosensor was realized.

Recent advances in the use of quantum dots for photoelectrochemical bioanalysis

Photoelectrochemical (PEC) bioanalysis is a newly developed technique for innovative biomolecular detection. Quantum dots (QDs) with unique photophysical properties are key components in realization of various exquisite PEC bioanalyses. Particularly, significant progress has been made in the QD-based PEC bioanalysis. In this work, we briefly summarize the most recent and important developments in the use of traditional and newly emerging QDs for novel PEC bioanalytical applications. The future prospects in this dynamic field are also highlighted.

A triple-amplification SPR electrochemiluminescence assay for chloramphenicol based on polymer enzyme-linked nanotracers and exonuclease-assisted target recycling

The present study aimed to explore a novel triple-amplification electrochemiluminescence (ECL) assay for detecting of chloramphenicol (CAP). This strategy was based on single-stranded DNA-binding protein (SSB) and horseradish peroxidase (HRP) enzyme-linked polymer (EnVision reagent, EV) labeled on Au nanoparticles (EV-Au-SSB) as nanotracer and exonuclease-assisted target recycling. The composite probes were prepared via immunoreactions between the CdS nanocrystal (CdS NC)-functionalized partial complementary DNA and aptamer (CdSNCs/Apt-ssDNA1) as capture probes, and EV-Au-SSB as nanotracer. When the composite probe solution co-existed with CAP and Exo I, the aptamer on the capture probes preferentially combined with CAP, and then CAP-Apt and nanotracer complex were released into the solution. Subsequently, Exo I in the solution could further digest the CAP-Apt from the 3'-end of the aptamer and release CAP, which could participate in further reaction with the probes. It was worth mentioning that EV contained a large number of HRPs on its dendritic chain. In the EV-Au-SSB, Au could enhance ECL intensity of CdS NCs by surface plasmon resonance. What's more, HRPs on EV could catalyze the reaction of H2O2, which could obviously enhance ECL intensity of CdS NCs. This study demonstrated excellent performance of the triple-amplification ECL assay, which makes this aptasensor system suitable and promising for the practical application of CAP residues in fish samples. Moreover, the assay might provide a promising avenue to develop efficient aptasensors to determine small-molecule harmful substances in environmental monitoring and food safety.

In situ generation of electron acceptor to amplify the photoelectrochemical signal from poly(dopamine)-sensitized TiO2 signal crystal for immunoassay

A photoelectrochemical protocol was designed for quantitative monitoring of tumor markers by utilizing poly(dopamine)-sensitized TiO₂ signal crystal.

A localized surface plasmon resonance-enhanced photoelectrochemical biosensing strategy for highly sensitive and scatheless cell assay under red light excitation

In this work, a novel photoelectrochemical biosensing strategy was designed for cell assay under 630 nm (red light) excitation.

Biomolecule-free, selective detection of o-diphenol and its derivatives with WS2/TiO2-based photoelectrochemical platform

Herein, a novel photoelectrochemical platform with WS2/TiO2 composites as optoelectronic materials was designed for selective detection of o-diphenol and its derivatives without any biomolecule auxiliary. First, catechol was chosen as a model compound for the discrimination from resorcinol and hydroquinone; then several o-diphenol derivatives such as dopamine, caffeic acid, and catechin were also detected by employing this proposed photoelectrochemical sensor. Finally, the mechanism of such a selective detection has been elaborately explored. The excellent selectivity and high sensitivity should be attributed to two aspects: (i) chelate effect of adjacent double oxygen atoms in the o-diphenol with the Ti(IV) surface site to form a five/six-atom ring structure, which is considered as the key point for distinction and selective detection. (ii) This selected WS2/TiO2 composites with proper band level between WS2 and TiO2, which could make the photogenerated electron and hole easily separated and results in great improvement of sensitivity. By employing such a photoelectrochemical platform, practical samples including commercial clinic drugs and human urine samples have been successfully performed for dopamine detection. This biomolecule-free WS2/TiO2 based photoelectrochemical platform demonstrates excellent stability, reproducibility, remarkably convenient, and cost-effective advantages, as well as low detection limit (e.g., 0.32 μmol L(-1) for dopamine). It holds great promise to be applied for detection of o-diphenol kind species in environment and food fields.

Strand displacement activated peroxidase activity of hemin for fluorescent DNA sensing

The toehold-mediated DNA strand displacement was utilized to regulate the catalytic activity of the peroxidase mimic hemin and design a fluorescent DNA sensing method with high specificity.

Photoelectrochemical bioanalysis: the state of the art

This review provides a panoramic snapshot of the state of the art in the dynamically developing field of photoelectrochemical bioanalysis.

Anatase TiO2 based photoelectrochemical sensor for the sensitive determination of dopamine under visible light irradiation

The sensitive photoelectrochemical determination of dopamine was achieved using an indium tin oxide electrode modified with TiO₂ nanoparticles.

An electrochemical peptide cleavage-based biosensor for prostate specific antigen detection via host–guest interaction between ferrocene and β-cyclodextrin

Here we have developed a “signal-on” peptide cleavage-based assay for sensitive and specific detection of prostate specific antigen (PSA) by coupling the host–guest interaction between ferrocene (Fc) and β-cyclodextrin (β-CD).

A biomimetic mussel-inspired photoelectrochemical biosensing chip for the sensitive detection of CD146

A universal biomimetic mussel-inspired photoelectrochemical biosensing chip was constructed by a polydopamine coating strategy.

Ultrasensitive photoelectrochemical immunoassay for matrix metalloproteinase-2 detection based on CdS:Mn/CdTe cosensitized TiO2 nanotubes and signal amplification of SiO2@Ab2 conjugates

An ultrasensitive photoelectrochemical sandwich immunoassay was developed to detect matrix metalloproteinase-2 (MMP-2, antigen, Ag) based on CdS:Mn/CdTe cosensitized TiO2 nanotubes (TiO2-NTs) and signal amplification of SiO2@Ab2 conjugates. Specifically, the TiO2-NTs electrode was first deposited with CdS:Mn by successive ionic layer adsorption and reaction technique and then further coated with CdTe quantum dots (QDs) via the layer-by-layer method, forming TiO2-NTs/CdS:Mn/CdTe cosensitized structure, which was employed as a matrix to immobilize capture MMP-2 antibodies (Ab1); whereas, SiO2 nanoparticles were coated with signal MMP-2 antibodies (Ab2) to form SiO2@Ab2 conjugates, which were used as signal amplification elements via the specific antibody-antigen immunoreaction between Ag and Ab2. The ultrahigh sensitivity of this immunoassay derived from the two major reasons as below. First, the TiO2-NTs/CdS:Mn/CdTe cosensitized structure could adequately absorb the light energy, dramatically promote electron transfer, and effectively inhibit the electron-hole recombination, resulting in significantly enhanced photocurrent intensity of the sensing electrode. However, in the presence of target Ag, the immobilized SiO2@Ab2 conjugates could evidently increase the steric hindrance of the sensing electrode and effectively depress the electron transfer, leading to obviously decreased photocurrent intensity. Accordingly, the well-designed photoelectrochemical immunoassay exhibited a low detection limit of 3.6 fg/mL and a wide linear range from 10 fg/mL to 500 pg/mL for target Ag detection. Meanwhile, it also presented good reproducibility, specificity, and stability and might open a new promising platform for the detection of other important biomarkers.

Bismuthoxyiodide nanoflakes/titania nanotubes arrayed p-n heterojunction and its application for photoelectrochemical bioanalysis

We have developed sensitive detection of cancer biomarker vascular endothelial growth factor (VEGF) using the p-n heterojunction comprised of p-type BiOI nanoflakes (NFs) array and n-type TiO₂ nanotubes (NTs) array. Due to the unique arrayed structure and the synergy effect of photoelectrochemistry in the formed p-n junction, the synthesized configuration has superior excitation efficiency and thus excellent photoresponsibility. Then, the fabricated p-n heterojunction was integrated with an exquisite bioassay protocol for addressing VEGF using a sandwich immunoassay with glucosedehydrogenase (GDH) as the enzyme tags. Due to the excellent performance of BiOI NFs array/TiO₂ NTs array and the ingenious signaling mechanism, the proposed system could achieve the sensitive and specific VEGF detection. This work not only presents a simple BiOI NFs array/TiO₂ NTs array p-n heterojunction for general applications in the broad photochemistry areas, but also opens a different horizon for current development of advanced PEC biomolecular detection.

Quantum dot-functionalized porous ZnO nanosheets as a visible light induced photoelectrochemical platform for DNA detection

This work reports the synthesis of novel CdTe quantum dot (QD)-functionalized porous ZnO nanosheets via a covalent binding method with (3-aminopropyl)triethoxysilane as a linker. The functional nanosheets showed an excellent visible-light absorbency and much higher photoelectrochemical activity than both CdTe QDs and ZnO nanosheets due to the porous structure and appropriate band alignment between the CdTe QDs and ZnO nanosheets. Using hydrogen peroxide as an electron acceptor the nanosheet-modified electrode showed a sensitive photocurrent response. This speciality led to a novel methodology for the design of hydrogen peroxide-related biosensors by the formation or consumption of hydrogen peroxide. Using biotin-labeled DNA as capture probe, a model biosensor was proposed by immobilizing the probe on a nanosheet-modified electrode to recognize target DNA in the presence of an assistant DNA, which produced a "Y" junction structure to trigger a restriction endonuclease-aided target recycling. The target recycling resulted in the release of biotin labeled to the immobilized DNA from the nanosheet-modified electrode, thus decreased the consumption of hydrogen peroxide by horseradish peroxidase-mediated electrochemical reduction after binding the left biotin with horseradish peroxidase-labeled streptavidin, which produced an increasing photoelectrochemical response. The 'signal on' strategy for photoelectrochemical detection of DNA showed a low detection limit down to the subfemtomole level and good specificity to single-base mismatched oligonucleotides. The sensitized porous ZnO nanosheets are promising for applications in both photovoltaic devices and photoelectrochemical biosensing.