Cathodic Photocurrent Research Articles

A cathodic photoelectrochemical self-powered aptasensor for ratiometric detection of cortisol based on PCN-224@graphene nanocomposites

Cathodic photoelectrochemical (PEC) sensors have garnered considerable research interest in bioanalysis for their ability to mitigate interference from photogenerated holes in concomitant reducing substances, but there remains a challenge to improve detection accuracy with rational strategies. In this study, a ratiometric assay was developed for cathodic PEC aptasensing of cortisol (COR), a stress hormone. Under visible-light exposure, porphyrin-based metal organic framework (PCN-224) and poly(diallyldimethylammonium chloride)-modified reduced graphene oxide (PrGO) composites were utilized as photoactive materials, enabling cathodic photocurrent production at 0 V. The spatially resolved dual photocathodes were combined with a COR-binding aptamer to selectively recognize the COR target, with one serving as the control. The ratio of the concentration-dependent inhibited photocurrent response (PI1) to the reference signal (PI2) from the control photocathode was employed for the sensitive COR bioassay. The proposed aptasensor revealed a broad linear range toward COR concentration from 0.4 nM to 800 nM, with a detection limit (3S/N) of 0.14 nM. The proposed sensor was successfully applied to real human serum samples, demonstrating promise in detecting disease markers in medical diagnostics.

An environment-friendly phosphotungstic acid catalyzed cross-dehydrogenative coupling reaction to synthesize 9-substituted-9H-xanthenes with photoelectrochemical performance

An environment-friendly phosphotungstic acid catalyzed cross-dehydrogenative coupling reaction for the synthesis of 9-substituted-9H-xanthenes under oxygen and solvent-free conditions have been developed. The economic and practical reaction exhibited good substrate applicability tolerance, various 9-substituted-9H-xanthenes were synthesized in moderate to excellent yields by tuning the ratio of xanthenes and ketones (22 examples, up to 99% yield). By testing the photoelectrochemical performance, some of the xanthene derivatives (10c, 12c, 13c and 2d) showed stable photocurrent value, especially 2d had better cathode photocurrent value and application potential.

Advancing polarity-transcendent design: Development of a photoelectrochemical sensor with extended detection range

In photoelectrochemical (PEC) sensors, traditional detection modes such as "signal-on", "signal-off", and "polarity-switchable" limit target signals to a single polarity range, necessitating novel design strategies to enhance the operational scope. To overcome this limitation, we propose, for the first time, a "polarity-transcendent" design concept that enables a continuous response across the polarity spectrum, significantly broadening the sensor's concentration detection range. This concept is exemplified in our new "background-enhanced signal-off polarity-switchable" (BESOPS) mode, where the model analyte let-7a activates a cascade shearing reaction of a DNAzyme walker in conjunction with CRISPR/Cas12a, quantitatively peeling off Cu2O-H2 strands at the Cu2O/TiO2 electrode interface to expose the TiO2 surface. This exposure generates an anodic photocurrent at the expense of the cathodic photocurrent from Cu2O/TiO2, facilitating a seamless transition of the target signal from cathodic to anodic. Through systematic experiments and comparative analyses, the BESOPS sensor demonstrates highly sensitive and precise quantification of let-7a, with a detection limit of 2.5 aM and a broad operating range of 10 aM to 10 nM. Its performance exceeds most reported sensor platforms, highlighting the significant potential of our polarity-transcendent design in expanding the operational range of PEC sensors. This innovative approach paves the way for developing next-generation PEC sensors with enhanced applicability and heightened sensitivity in various critical fields.

Sensitive photoelectrochemical detection of Cr(Ⅵ) based on the suppression of background photocurrent

A photoelectrochemical (PEC) sensor based on a BiVO4 semiconductor and gold nanoparticles (AuNPs) was successfully prepared for the sensitive detection of Cr(Ⅵ) ions. The calcination temperature was found to be very important for the PEC properties of BiVO4. The BiVO4-modified indium tin oxide electrode (ITO/BiVO4) calcined at 300 °C generated a low cathodic photocurrent response under light irradiation. BiVO4/AuNPs materials were coupled via electrostatic adsorption to enhance the photoelectric conversion performance of BiVO4. The use of self-assembled monolayers (SAMs) to modify electrodes reduce the background current. The developed ITO/BiVO4/AuNPs/L-Cys PEC sensor was used to detect of Cr(VI). The Cr(Ⅵ) ion concentrations showed a good linearity between 10 pM and 1 μM with a detection limit of 9.1 pM (S/N = 3). The prepared PEC sensor exhibited high sensitivity, a wide linear range, and good selectivity. This work provides a promising platform for the analytical detection of heavy metal ions.

Novel “Signal-On” photoelectrochemical assay by regulating the release of cationic dyes with the utilization of target-specific enzymolysis hydrogels

Targeted response-based controlled release strategy exhibits high specificity and sensitivity in many biomedical applications. In this paper, we report a novel and simple “signal-on” photoelectrochemical (PEC) assay strategy, which regulates the release of cationic dyes through the utilization of target-specific enzymolysis hydrogel. The cationic dye crystal violet (CV) embedded in the hyaluronic acid (HA) hydrogel was released in the presence of hyaluronidase (HAase) and increased the cathodic photocurrent of BiOBr nanoflowers. The cathodic photocurrent response is linear with the logarithm of HAase activity in the range of 0.10–120 U/mL, with an ultralow detection limit of 0.034 U/mL detected. Our work provides a simple and efficient strategy to detect HAase activity by monitoring the enzyme response of hydrogel-controlled release photosensitizer, which is expected to be able to provide an efficient strategy for early clinical diagnosis of some other diseases and meet the ever-increasing needs in pharmaceutical and medical fields.

Enhancing Photocathodic Performances of Particulate-CuGaS2-Based Photoelectrodes via Conjugation with Conductive Organic Polymers for Efficient Solar-Driven Hydrogen Production and CO2 Reduction.

Modification with conductive organic polymers consisting of a thiophane- or pyrrole-based backbone improved the cathodic photocurrent of a particulate-CuGaS2-based photoelectrode under simulated solar light. Among these polymers, poly(3,4-ethylenedioxythiophene) (PEDOT) was the most effective in the improvements, providing a photocurrent 670 times as high as that of the bare photocathode. An incident-photon-to-current efficiency (IPCE) for water reduction to form H2 under monochromatic light irradiation (450 nm at 0 V vs RHE) was ca. 11%. The most important point is that modification of the conductive organic polymers does not involve any vacuum processes. This importance lies in the use of an electrochemically oxidative polymerization, not in a physical process such as vapor deposition of metal conductors. This is expected to be advantageous in the large-scale application of photocathodes consisting of particulate photocatalyst materials toward industrial solar-hydrogen production using photoelectrochemical-cell-based devices. Artificial photosynthesis of water splitting and CO2 reduction under simulated solar light was demonstrated by combining the PEDOT-modified CuGaS2 photocathode with a CoOx-loaded BiVO4 photoanode. Furthermore, how the cathodic photocurrent of the particulate-CuGaS2-based photocathode was drastically improved by the modification was clarified based on various characterizations and control experiments as follows: (1) selectively filling cavities between the particulate CuGaS2 photocatalysts and a conductive substrate (FTO; fluorine-doped tin oxide) with the polymers and (2) using a large driving force for carrier transportation governed by the polymers' redox potentials adjusted by functional groups.

Detection of alkaline phosphatase activity with a CsPbBr3/Y6 heterojunction-based photoelectrochemical sensor.

An ultra-sensitive photoelectrochemical (PEC) sensor based on perovskite composite was developed for the determination of alkaline phosphatase (ALP) in human serum. In contrast toCsPbBr3 or Y6 that generated anodic current, the heterojunction of CsPbBr3/Y6 promoted photocarriers to separate and generated cathodic photocurrent. Ascorbic acid (AA) was produced by ALP hydrolyzing L-ascorbic acid 2-phosphate trisodium salt (AAP), which can combine with the holes on the photoelectrode surface, accelerating the transmission of photogenerated carriers, leading to enhanced photocurrent intensity. Thus, the enhancement of PEC current was linked to ALP activity. The PEC sensor exhibits good sensitivity for detection of ALP owing to the unique photoelectric properties of the CsPbBr3/Y6 heterojunction. The detection limit of the sensor was 0.012 U·L-1 with a linear dynamic range of 0.02-2000 U·L-1. Therefore, this PEC sensing platform shows great potential for the development of different PEC sensors.

Metal organic framework-derived CuO/Cu2O polyhedron-CdS quantum dots double Z-scheme heterostructure for cathodic photoelectrochemical detection of Hg2+ in food and environment

This study employed an innovative copper oxide/cuprous oxide (CuO/Cu2O) polyhedron‑cadmium sulphide quantum dots (CdS QDs) double Z-scheme heterostructure as a matrix for the cathodic PEC determination of mercury ions (Hg2+). First, the CuO/Cu2O polyhedral composite was prepared by calcining a copper-based metal organic framework (Cu-MOF). Subsequently, the amino-modified CuO/Cu2O was integrated with mercaptopropionic acid (MPA)-capped CdS QDs to form a CuO/Cu2O polyhedron-CdS QDs double Z-scheme heterostructure, producing a strong cathodic photocurrent. Importantly, this heterostructure exhibited a specifically reduced photocurrent for Hg2+ when using CdS QDs as Hg2+-recognition probe. This was attributed to the extreme destruction of the double Z-scheme heterostructure and the in situ formation of the CuO/Cu2O-CdS/HgS heterostructure. Besides, p-type HgS competed with the matrix for electron acceptors, further decreasing the photocurrent. Consequently, Hg2+ was sensitively assayed, with a low detection limit (0.11 pM). The as-prepared PEC sensor was also used to analyse Hg2+ in food and the environment.

A triple-amplified electrochemical-photoelectrochemical dual-mode biosensing platform for viral gene assay based on catalytic hairpin assembly, CRISPR-Cas12a and liposome-entrapped bifunctional methylene blue

Taking SARS-CoV-2 RNA-dependent RNA polymerase (RdRp) gene as the model due to the great destructiveness of COVID-19 in the past years, a triple-amplified electrochemical-photoelectrochemical (EC-PEC) dual-mode biosensing platform was constructed for viral gene assay based on catalytic hairpin assembly (CHA), CRISPR-Cas12a and liposome-entrapped bifunctional methylene blue. Firstly, the SARS-CoV-2 RdRp gene triggered CHA nonenzymatic amplification process to produce large amounts of double-stranded DNA (dsDNA) that could activate CRISPR-Cas12a trans-cleavage ability. Subsequently, the activated CRISPR-Cas12a trans-cleaved nearby ssDNA carrying methylene blue (MB)-encapsulated liposome sphere (MELS) and streptavidin-modified magnetic bead (SMB), and lots of MELS were released. After magnetic separation, MELS was lysed by Triton X-100, releasing a large quantity of bifunctional MB molecules that not only generate an obvious EC signal originated from the electro-oxidation of MB, but also effectively induce the photocurrent-polarity-switching of the Sb2S3 NRs-modified photoelectrode from cathodic photocurrent to anodic photocurrent and generate a large anodic photocurrent. Based on the combination of the above triple amplification processes with MB-induced photocurrent-polarity-switching and EC-PEC dual-mode sensing strategies, the SARS CoV-2 RdRp gene was sensitively, selectively and accurately assayed with a linear response range of 0.1 fM – 10nM (1 aM – 10nM) and a detection limit of 69.6 aM (0.11 aM) for EC (PEC) method. The proposed EC-PEC dual-mode biosensor is also easily extended to the analysis of other viral nucleic acid by changing the related sequences of H1 and H2 DNAs, providing a new way in the early diagnosis and epidemic control of diseases caused by viruses.

A signal-switchable photoelectrochemical biosensor for ultrasensitive detection of long non-coding RNA in cancer cells

Long non-coding RNA (LncRNA) as an emerging tumor biomarker plays a key factor in the early diagnosis of cancer. Herein, an innovative signal-switchable photoelectrochemical (PEC) biosensor based on ZrO2@CuO bimetallic oxides and T7 Exo-assisted signal amplification is reported for the ultrasensitive and selective detection of lncRNA (HOX gene antisense intergenic RNA, HOTAIR) in cancer cells. Firstly, MOFs-derived TiO2 nanodisks as an excellent photoactive material show an anodic background signal. When target lncRNA exists, the abundant auxiliary DNA1 is freed from T7 Exo-assisted cycle signal amplification, and then competitively hybridizes with auxiliary DNA2 on the electrode. Subsequently, bimetallic MOFs-derived ZrO2@CuO octahedra with a high specific surface area and porous structure are introduced into TiO2 nanodisks-modified biosensor, which appears a cathodic photocurrent and achieves a switchable signal. The developed signal-switchable PEC biosensor shows ultrasensitive detection of lncRNA HOTAIR with a detection limit of 0.12 fM, and can eliminate the false interference. Importantly, the established PEC biosensor has good correlation with RT-qPCR analysis (P < 0.05) for the quantification of lncRNA HOTAIR in cancer cells, which has great potential application for biomarker detection in the early diagnosis of cancer.

In situ polymerised polyaniline films over multi-walled carbon nanotubes coatings for enhanced photoelectrochemical performance

Polyaniline (PANI), which is a π-conjugated polymer, has stood out as a promising candidate for dihydrogen generation in photoelectrochemical (PEC) cells owing to its suitable optoelectronic properties and excellent stability. Nevertheless, the PEC performance of this material is still far from adequate for technological applications. Herein, we have focused on improving the PEC performance of PANI films by combining this polymer with multi-walled carbon nanotubes (MWCNTs) layers. Specifically, we have assessed the PEC activity of the in situ polymerised PANI films onto FTO substrates coated with different amounts of MWCTNs for the hydrogen evolution reaction (HER). The FTO/MWCNTs/PANI films with the optimum deposited amount of MWCNTs (i.e., 30 μL) featured a 2.4-fold increase of the cathodic photocurrent density response for the HER compared to that of FTO/PANI film. Moreover, the FTO/(30 μL)-MWCNTs/PANI films exhibited good PEC stability, as observed by the relatively low cathodic photocurrent density decay of up to 7% during 3720 s of stability test. Based on joint analyses of physical and PEC characterisation, the improved PEC performance for the FTO/(30 μL)-MWCNTs/PANI films were assigned to the combined contribution of the following factors: (i) enhancement of light absorption; (ii) possible improvement of excitons dissociation; (iii) minimisation of the electron-hole recombination process; and (iv) facilitation of electrons transfer at the PANI|electrolyte interface for the HER. The enhancement of PEC performance achieved in this work for the fully organic photocathode composed of MWCNTs/PANI paves the way to invest in additional modifications seeking to further improve the dissociation of excitons and the interfacial transfer of charge carriers for the light-driven HER.

Porous Electropolymerized Films of Ruthenium Complex: Photoelectrochemical Properties and Photoelectrocatalytic Synthesis of Hydrogen Peroxide

The photoelectrochemical cells (PECs) performing high-efficiency conversions of solar energy into both electricity and high value-added chemicals are highly desirable but rather challenging. Herein, we demonstrate that a PEC using the oxidatively electropolymerized film of a heteroleptic Ru(II) complex of [Ru(bpy)(L)2](PF6)2 Ru1 {bpy and L stand for 2,2′-bipyridine and 1-phenyl-2-(4-vinylphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline respectively}, polyRu1, as a working electrode performed both efficient in situ synthesis of hydrogen peroxide and photocurrent generation/switching. Specifically, when biased at −0.4 V vs. saturated calomel electrode and illuminated with 100 mW·cm−2 white light, the PEC showed a significant cathodic photocurrent density of 9.64 μA·cm−2. Furthermore, an increase in the concentrations of quinhydrone in the electrolyte solution enabled the photocurrent polarity to switch from cathodic to anodic, and the anodic photocurrent density reached as high as 11.4 μA·cm−2. Interestingly, in this single-compartment PEC, the hydrogen peroxide yield reached 2.63 μmol·cm−2 in the neutral electrolyte solution. This study will serve as a guide for the design of high-efficiency metal-complex-based molecular systems performing photoelectric conversion/switching and photoelectrochemical oxygen reduction to hydrogen peroxide.

Universal photoelectrochemical aptasensing platform for antibiotic based on CuInS2/rGO and triplex DNA

In this work, a universal and convenient photoelectrochemical (PEC) biosensor was proposed to detect antibiotic on the basis of CuInS2/rGO and triplex DNA molecular switch. High performance photoactive structure was formed via p-type CuInS2 nanosphere complexed with rGO, which was employed to enhance the cathode photocurrent. Capture probe (CP) was conjugated onto the photoactive interface through covalent bonding. In the absence of target, the triplex DNA (THMS) was in a closed state. After introducing a target, the interaction between the target and the specific ring part DNA fragment leaded to the dissociation of the THMS and thereby liberated the single strand DNA (SP). The above identification process was completed in the homogeneous solution. Then, SP was captured to the electrode by CP and hybridized to form dsDNA. The steric effect of dsDNA hindered the interfacial charge transfer, resulting in signal-off photocurrent output. By only altering the specific loop section sequence of THMS, different targets can release the same SP, and can be detected on the same sensing platform under the same testing conditions. As proof of principle, three kinds of antibiotics amoxicillin (AMOX), ampicillin (AMP) and tobramycin (TOB) was detected, achieving limit of detection values of 3.17 pM, 0.63 nM and 2.81 fM, respectively. This approach was also used to detect antibiotic residues in food and environmental samples, which provides a promising paradigm for developing universal, high-performance and convenient PEC biosensing platform.

Sensitive photochemical detection of Pb2+ based on the "on-off-on" strategy coupled with adsorption

A photoelectrochemical (PEC) sensor, utilizing the semiconductor BiVO4 and gold nanoparticles (AuNPs) modified with glutathione (GSH), was successfully fabricated for the sensitive detection of Pb2+ ions. The calcinated BiVO4-modified indium tin oxide (ITO) electrode (ITO/BiVO4) generated a low cathodic photocurrent response under light irradiation. The photocurrent at ITO/BiVO4/AuNPs photoelectrode increased significantly due to the plasmon enhancement of AuNPs and the electron transfer. This enhancement photocurrent intensity was largely suppressed by introducing GSH to form ITO/BiVO4/AuNPs/GSH. It minimized the base photocurrent of the photoelectrode. Upon the addition of Pb2+ ions in the cell, they were adsorbed on the electrode surface through the interaction with the two carboxyl groups in GSH. Subsequently, Pb2+ ions, serving as electron acceptors, underwent reduction under light irradiation, leading to increase in photocurrent intensity again. Therefore, a signal "on-off-on" PEC sensor was developed for the detection of Pb2+ ions. The concentration of Pb2+ ions show a good linearity between 0.1 pM and 10 μM with a detection limit of 0.08 pM (S/N = 3). The prepared PEC sensor shows high sensitivity, a wide linear range, and good selectivity. This work provides a promising platform for the analytical detection of heavy metal ions.

Enhanced electrocatalytic activity in hydrogen evolution reaction using 2D/2D nanohybrids of ruthenate nanoflakes and graphitic carbon nitride.

Photoelectrochemical and electrochemical water splitting was examined using ruthenate nanoflake (RuNF) and graphitic carbon nitride (g-C3N4) hybrids. A two-dimensional and visible-light-responsive photocatalyst g-C3N4 was hybridized with the RuNFs that we recently synthesized via a bottom-up process in aqueous solution, yielding 2D/2D nanocomposites. The influence of the 2D/2D nanocomposites on oxygen and hydrogen evolution during photoelectrochemical and electrochemical water splitting was investigated. First, electrolysis of a Na2SO4 aqueous solution was conducted with intermittent photo-irradiation. Both the g-C3N4 electrode and the RuNF/g-C3N4 hybrid electrode provided anodic and cathodic photocurrents at high and low potentials, respectively; however, the copresence of RuNFs decreased the photocurrents, probably because the RuNFs retarded the light absorption by g-C3N4. Moreover, the use of RuNF/g-C3N4 hybrids as electrodes facilitated both the oxygen and hydrogen evolution reactions without photo-irradiation. However, for the oxygen evolution reaction, the effect of the RuNFs was similar to that of RuO2 nanoparticles, indicating that the influence of the type and morphology of ruthenium species on the oxygen evolution reaction was small. Conversely, irrespective of the pH of the aqueous solutions in an electrolytic bath, the 2D/2D nanostructure of RuNFs and g-C3N4 decreased the overpotential of the hydrogen evolution reaction. However, the use of RuO2 particles instead of RuNFs did not cause such a phenomenon. Thus, it was revealed that the RuNFs synthesized via a bottom-up process were useful as a co-catalyst for the hydrogen evolution reaction.

On the structural evolution of nanoporous optically transparent CuO photocathodes upon calcination for photoelectrochemical applications.

Copper oxides are promising photocathode materials for solar hydrogen production due to their narrow optical band gap energy allowing broad visible light absorption. However, they suffer from severe photocorrosion upon illumination, mainly due to copper reduction. Nanostructuring has been proven to enhance the photoresponse of CuO photocathodes; however, there is a lack of precise structural control on the nanoscale upon sol-gel synthesis and calcination for achieving optically transparent CuO thin film photoabsorbers. In this study, nanoporous and nanocrystalline CuO networks were prepared by a soft-templating and dip-coating method utilizing poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic® F-127) as a structure-directing agent, resulting for the first-time in uniformly structured, crack-free, and optically transparent CuO thin films. The photoelectrochemical properties of the nanoporous CuO frameworks were investigated as a function of the calcination temperature and film thickness, revealing important information about the photocurrent, photostability, and photovoltage. Based on surface photovoltage spectroscopy (SPV), the films are p-type and generate up to 60 mV photovoltage at 2.0 eV (0.050 mW cm-2) irradiation for the film annealed at 750 °C. For these high annealing temperatures, the nanocrystalline domains in the thin film structure are more developed, resulting in improved electronic quality. In aqueous electrolytes with or without methyl viologen (as a fast electron acceptor), CuO films show cathodic photocurrents of up to -2.4 mA cm-2 at 0.32 V vs. RHE (air mass (AM) 1.5). However, the photocurrents were found to be entirely due to photocorrosion of the films and decay to near zero over the course of 20 min under AM 1.5 illumination. These fundamental results on the structural and morphological development upon calcination provide a direction and show the necessity for further (surface) treatment of sol-gel derived CuO photocathodes for photoelectrochemical applications. The study demonstrates how to control the size of nanopores starting from mesopore formation at 400 °C to the evolution of macroporous frameworks at 750 °C.

A sensitive signal off photoelectrochemical aptasensor based on CuO nanosheets @Au nanoflowers for the detection of chloramphenicol

A signal off type photoelectrochemical (PEC) aptasensor was constructed for the sensitive detection of chloramphenicol based on CuO nanosheets (CuO NSs) and gold nanoflowers (Au NFs) modified indium tin oxide (ITO) electrode. CuO NSs was p-type photoactive semiconductor materials, which had narrow band gap and high absorption rate of visible light. After combining with Au NFs, the composite CuO NSs@Au NFs produced a strong cathodic photocurrent for the excellent electron conductivity, large specific surface area and Surface Plasmon Resonance effect (SPR) of Au NFs. At the same time, Au NFs provided a binding site for aptamer, which greatly improved the sensitivity of the constructed sensing platform. After the target chloramphenicol (CAP) was specifically captured by the aptamers on the electrode, the formed bioconjugates seriously hindered the transfer of electrons and the absorption of light and caused a reduced photocurrent. For the detection of CAP, this signal off type PEC aptasensor had a linear range of 5 pM-300 nM and a limit of detection of 49.9 fM (S/N = 3) with good stability, selectivity and reproducibility. Meanwhile, the method had satisfactory recovery results in the detection of CAP in real-life samples such as milk, tap water, honey and chloramphenicol eye drops.

A Multi-Pyridine-Anchored and -Linked Bilayer Photocathode for Water Reduction.

The development of efficient photocathodes is of critical importance for the constructions of promising tandem photo-electrochemical cells. Most known dye-sensitized photocathodes are prepared with the conventional carboxylic or phosphonic acid anchors and require the presence of other terminal linking groups to connect catalysts; they suffer from high synthetic difficulty and low adsorption stability in aqueous media. Here, a compact bilayer photocathode has been prepared by using a pyrene-based photosensitizer with multiple terminal pyridine moieties as both the anchoring and linking groups to connect a Co hydrogen-evolution catalyst to the NiO substrate. The catalyst and dye molecule are assembled in a layer-by-layer manner on NiO through the metal-pyridine coordination. This photocathode exhibits good dye adsorption stability in aqueous media. A stable cathodic photocurrent of 70 μA cm-2 was achieved, with H2 being generated at the photocathode under the visible-light irradiation. The Faraday efficiency of H2 evolution was estimated to be 9.1 %. Transient absorption spectral studies suggest that the interfacial hole transfer occurs within a few picoseconds. The integration of the organic photosensitizer with pyridine anchoring and linking groups is expected to provide a simple method for the fabrication of stable and efficient photocathodes.

Photocurrent-polarity switching between methylene blue-loaded liposome and iodine-doped BiOCl for in-situ amplified immunoassay

This work designed a liposome-mediated photocurrent polarity switching immunosensor depending on the reversed photocurrent of iodine-doped BiOCl (I-BOC) nanoflowers induced by the released methylene blue (MB) for the detection of prostate-specific antigen (PSA). Initially, MB-loaded liposomes as indicators were confined within the microplates to participate in the sandwiched immunoreaction and lysed under the treatment of Triton X-100 to release numerous MB. Owing to the host-guest recognition between β-cyclodextrin (β-CD) and MB, the released MB was immobilized on the β-CD-modified I-BOC/FTO electrode and triggered the photocurrent polarity reversal from cathodic photocurrent to anodic photocurrent. The sensing platform realized an accurate and sensitive assay of PSA due to the effective elimination of false-positive/negative signals in a linear range of 0.02–50 ng mL−1 with a limit of detection of 12 pg mL−1. Furthermore, this work not only conjugated liposome-assisted signal amplification strategy with the photocurrent polarity switching system but also provided a novel pathway for various protein determinations.

Photocurrent Polarity Reversal Induced by Electron-Donor Release for the Highly Sensitive Photoelectrochemical Detection of Vascular Endothelial Growth Factor 165.

Photocurrent polarity reversal is a switching process between the anodic and cathodic pathways and is critical for eliminating false positivity and improving detection sensitivity in photoelectrochemical (PEC) sensing. In this study, we construct a PEC sensor with excellent photocurrent polarity reversal induced by ascorbic acid (AA) as an electron donor with the energy level matching the photoactive material zirconium metal-organic framework (ZrMOF). The ZrMOF-modified electrode demonstrates cathodic photocurrent in the presence of O2 as an electron acceptor, while the anodic photocurrent is generated in the presence of AA, achieving photocurrent polarity reversal. By the in situ release of AA from AA-encapsulated apoferritin modified with DNA 2 (AA@APO-S2) as a detection tag in the presence of trypsin after the recognition of hairpin DNA-modified indium tin oxide to the reaction product of aptamer/DNA 1 with the target protein and the following rolling cycle amplification for introducing the detection tag to the sensing interface, the reversed photocurrent shows an enhanced photocurrent response to the target protein, leading to a highly sensitive PEC sensing strategy. This strategy realizes the detection of vascular endothelial growth factor 165 with good specificity, a wide linear range, and a low detection limit down to 5.3 fM. The actual sample analysis offers the detection results of the proposed PEC sensor comparable to those of commercial enzyme-linked immunosorbent assay tests, indicating the promising application of the photocurrent polarity reversal-based PEC sensing strategy in biomolecule detection and clinical diagnosis.