Application of ZnO/graphene and S6 aptamers for sensitive photoelectrochemical detection of SK-BR-3 breast cancer cells based on a disposable indium tin oxide device

ZnO/graphene (ZnO/G) composite and S6 aptamer were employed to sensitive photoelectrochemical (PEC) strategy for the specific detection of SK-BR-3 cancer cells based on a portable indium tin oxide microdevice. ZnO/G composite was synthesized using a facile ultrasonic method, and then applied to improve the PEC performance due to the unique hollow structure of ZnO naospheres and the superior properties of graphene. Subsequently, S6 aptamer was applied to this specific detection of SK-BR-3 cancer cells. And the concentration of SK-BR-3 cells was measured with a low detection limit of 58 cells mL(-1) and a wide linear range of 1×10(2)-1×10(6) cells mL(-1), through the decrease in photocurrent intensity resulting from the increase in steric hindrances when specifically recognized with S6 aptamers. Excellent discrimination against target and analogous cells was demonstrated, indicating the high selectivity of the proposed cell sensor. Our work also demonstrated a sensitive, stable and low cytotoxicity approach for early and accurate detection of cancer cells.

Photoelectrochemical biosensor for microRNA detection based on a MoS2/g-C3N4/black TiO2 heterojunction with Histostar@AuNPs for signal amplification

Herein, a novel photoelectrochemical (PEC) biosensor was developed for the ultrasensitive detection of microRNA-396a based on a MoS₂/g-C₃N₄/black TiO₂ heterojunction as the photoactive material and gold nanoparticles carrying Histostar antibodies (Histostar@AuNPs) for signal amplification. Briefly, MoS₂/g-C₃N₄/black TiO₂ was deposited on an indium tin oxide (ITO) electrode surface, after which gold nanoparticles (AuNPs) and probe DNA were assembled on the modified electrode. Hybridization with miRNA-396a resulted in a rigid DNA: RNA hybrid being formed, which was recognized by the S9.6 antibody. The captured antibody can further conjugate with the secondary IgG antibodies of Histostar@AuNPs, thereby leading to the immobilization of horse radish peroxidase (HRP). In the presence of HRP, the oxidation of 4-chloro-1-naphthol (4-CN) by H₂O₂ was accelerated, producing the insoluble product benzo-4-chlorohexadienone on the electrode surface and causing a significant decrease in the photocurrent. The developed biosensor could detect miRNA-396a at concentrations from 0.5 fM to 5000 fM, with a detection limit of 0.13 fM. Further, the proposed method can also be used to investigate the effect of heavy metal ions on the expression level of miRNAs. Results suggest that the biosensor developed herein offers a promising platform for the ultrasensitive detection of miRNA.

A sensitive Potentiometric resolved ratiometric Photoelectrochemical aptasensor for Escherichia coli detection fabricated with non-metallic nanomaterials

In this work, a sensitive potentiometric resolved ratiometric photoelectrochemical aptasensor for Escherichia coli (E. coli) detection was successfully fabricated with non-metallic nanomaterials. To avoid the use of precious metals or heavy metals, three-dimensional graphene hydrogel-loaded carbon quantum dots (C-dots/3DGH) and graphene-like carbon nitride (g-C₃N₄) with excellent PEC activity and matched potential were prepared. These two materials were modified onto two adjacent areas on the ITO electrode. By applying different bias voltage, the cathodic current generated by C-dots/3DGH and the anodic current generated by g-C₃N₄ can be clearly distinguished and would not interfere with one another. Then E. coli aptamer was modified onto the surface of C-dots/3DGH. In the presence of targets, the binding of E. coli with aptamer lead to the steric hindrance greatly increased and the cathodic current decreased significantly. Meanwhile, the anodic current generated by g-C₃N₄ was not influenced and it can serve as a stable reference to evaluate the environmental factors. Therefore, the concentration of E. coli can be quantified by the ratio of cathodic current to anodic current, which can effectively eliminate these analyte-independent factors and provide a more precise analysis. In addition, this ratiometric PEC biosensor also showed a good sensitivity and a wide linear range (2.9 cfu/mL to 2.9 × 10⁶ cfu/mL).

Nanostructured photoelectrochemical biosensor for highly sensitive detection of organophosphorous pesticides

A sensitive photoelectrochemical (PEC) biosensor for detection of organophosphorus pesticides (OPs) using the nanocomposite of CdSe@ZnS quantum dots (QDs) and graphene deposited on the ITO coated glass electrode as a photoactive electrode is presented. The integration of CdSe@ZnS/graphene nanocomposite with biomolecules acetylcholinesterase (AChE) as a biorecognition element yields a novel biosensing platform. Under visible light irradiation, the AChE-CdSe@ZnS/graphene nanocomposite can generate a stable photocurrent and the photocurrent is found to be inversely dependent on the concentration of OPs. Under the optimal experimental conditions, the photocurrents were proportional to the logarithm of paraoxon and dichlorvos within the concentration range of 10(-12)-10(-6) M. The detection limits (LOD) of the proposed biosensor for paraoxon and dichlorvos are as low as 10(-14) M and 10(-12) M. The photoelectrochemical biosensor shows good sensitivity, reproducibility, stability, and could be successfully applied to detection of OPs in real fruit samples.

Enhanced photoelectrochemical property of ZnO nanorods array synthesized on reduced graphene oxide for self-powered biosensing application

We have realized the direct synthesis of ZnO nanorods (ZnO NRs) array on reduced graphene layer (rGO), and demonstrated the enhanced photoelectrochemical (PEC) property of the rGO/ZnO based photoanode under UV irradiation compared with the pristine ZnO NRs array. The introduction of the rGO layer resulted in a favorable energy band structure for electron migration, which finally led to the efficient photoinduced charge separation. Such nanostructure was subsequently employed for self-powered PEC biosensing of glutathione in the condition of 0 V bias, with a linear range from 10 to 200 µM, a detection limit of 2.17 µM, as well as excellent selectivity, reproducibility and stability. The results indicated the rGO/ZnO nanostructure is a competitive candidate in the PEC biosensing field.

A photoelectrochemical biosensor for o-aminophenol based on assembling of CdSe and DNA on TiO2 film electrode

A novel photoelectrochemical (PEC) biosensing platform was constructed by assembling CdSe quantum dots (QDs) and DNA on liquid phase deposited TiO2 (DNA-CdSe/TiO2) film electrode. The transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis indicated that CdSe QDs were homogeneously assembled on TiO2 film. The UV-visible diffuse reflectance spectra (DRS) showed that CdSe and DNA could effectively enhance the absorption of TiO2 film to visible light. The obtained electrode showed a sensitive PEC response to o-aminophenol (OAP) under visible light irradiation. Due to the interaction between DNA and OAP, the response of OAP was improved by DNA immobilized on the sensing film. Under optimized conditions, the photocurrent was linearly proportional to OAP in the concentration range from 4.0 × 10(-7) to 2.7 × 10(-5) mol L(-1), with a detection limit (3S/N) of 8.0 × 10(-8) mol L(-1). The novel strategy could provide a fast and sensitive method for OAP determination.

A signal "on" photoelectrochemical biosensor for assay of protein kinase activity and its inhibitor based on graphite-like carbon nitride, Phos-tag and alkaline phosphatase

A highly sensitive and selective photoelectrochemical (PEC) biosensor is fabricated for the detection of protein kinase activity based on visible-light active graphite-like carbon nitride (g-C3N4) and the specific recognition utility of Phos-tag for protein kinase A (PKA)-induced phosphopeptides. For assembling the substrate peptides, g-C3N4 and gold nanoparticles (g-C3N4-AuNPs) complex is synthesized and characterized. When the immobilized peptides on g-C3N4-AuNPs modified ITO electrode are phosphorylated under PKA catalysis, they can be specifically identified and binded with biotin functionalized Phos-tag (Phos-tag-biotin) in the presence of Zn(2+). Then, through the specific interaction between biotin and avidin, avidin functionalized alkaline phosphatase (avidin-ALP) is further assembled to catalyze its substrate of l-ascorbic acid-2-phosphate trisodium salt (AAP) to produce electron donor of ascorbic acid (AA), resulting an increased photocurrent compared with the absence of phosphorylation event. Based on the specific identification effect of Phos-tag, the fabricated biosensor presents excellent selectivity for capturing the phosphorylated serine residues in the substrate peptides. With the good photoactivity of g-C3N4 and ALP-catalyzed signal amplification, the fabricated biosensor presents high sensitivity and low detection limit (0.015 unit/mL, S/N = 3) for PKA. The applicability of this PEC biosensor is further testified by the evaluation of PKA inhibition by HA-1077 with the IC50 value of 1.18μM. This new strategy is also successfully applied to detect the change of PKA activity in cancer cell lysate with and without drug stimulation. Therefore, the developed PEC method has great potential in screening of kinase inhibitors and highly sensitive detection of kinase activity.

A highly selective photoelectrochemical biosensor for uric acid based on core-shell Fe3O4@C nanoparticle and molecularly imprinted TiO2

Combining the surface modification and molecular imprinting technique, a novel photoelectrochemical sensing platform with excellent photochemical catalysis and molecular recognition capabilities was established for the detection of uric acid based on the magnetic immobilization of Fe3O4@C nanoparticles onto magnetic glassy carbon electrode (MGCE) and modification of molecularly imprinted TiO2 film on Fe3O4@C. The developed biosensor was highly sensitive to uric acid in solutions, with a linear range from 0.3 to 34µM and a limit of detection of 0.02μM. Furthermore, the biosensor exhibited outstanding selectivity while used in coexisting systems containing various interferents with high concentration. The practical application of the biosensor was also realized for the selective detection of uric acid in spiked samples. The study made a successful attempt in the development of highly selective and sensitive photoelectrochemical biosensor for urine monitoring.

Photoelectrochemical biosensing of disease marker on p-type Cu-doped Zn0.3Cd0.7S based on RCA and exonuclease III amplification

In this work, a new "signal-on" split-type photoelectrochemical (PEC) sensing platform for prostate-specific antigen (PSA) detection was successfully constructed using p-type Cu-doped Zn_0.3Cd_0.7S as the photosensitive semiconductor material and target-triggered rolling circle amplification (RCA) for signal amplification. The signal derived from Cu-doped Zn_0.3Cd_0.7S was amplified by hemin/G-quadruplex. Upon target PSA introduction, the aptamer-primer probe (apt-pri) was captured by capture antibody-conjugated magnetic bead (MB-mAb) to form the sandwiched MB-mAb/PSA/apt-pri. The complex could initiate the RCA reaction to produce a long single-stranded DNA that provided binding sites for G-rich DNA and to form long single-stranded DNA/G-quadruplex/hemin. Upon the addition of exonuclease III (Exo III), the hemin/G-quadruplex immobilized on the RCA long product could be released by the digestion of Exo III. The hemin/G-quadruplex complexes in this study were used as efficient electron acceptors to neutralize the photoelectrons generated from the semiconductor and hindered the recombination of charges, thus enhancing the photocurrent. Under the optimum conditions, the developed sensing system displayed a good analytical performance with a linear range of 0.05-40 ng mL^-1 PSA and a detection limit of 16.3 pg mL^-1. Furthermore, good selectivity, high anti-interference ability, satisfactory reproducibility, and good accuracy were also achieved. These prominent analytical properties revealed that our strategy might be a potential and reliable tool for the detection of PSA.

Ultrasensitive photoelectrochemical aptasensor for detecting telomerase activity based on Ag2S/Ag decorated ZnIn2S4/C3N4 3D/2D Z-scheme heterostructures and amplified by Au/Cu2+-boron-nitride nanozyme

Enzyme-mediated signal amplification strategies have gained substantial attention in photoelectrochemical (PEC) biosensing, while natural enzyme on the photoelectrode inevitably obstructs the interfacial electron transfer, in turn deteriorating the photocurrent responses. Herein, Au nanoparticles and Cu²⁺-modified boron nitride nanosheets (AuNPs/Cu²⁺-BNNS) behaved as nanozyme to achieve remarkable magnification in the PEC signals from a novel signal-off aptasensor for ultra-sensitive assay of telomerase (TE) activity based on Ag₂S/Ag nanoparticles decorated ZnIn₂S₄/C₃N₄ Z-scheme heterostructures (termed as Ag₂S/Ag/ZnIn₂S₄/C₃N₄, synthesized by hydrothermal treatment). Specifically, telomerase primer sequences (TS) were extended by TE in the presence of deoxyribonucleoside triphosphates (dNTPs), which was directly bond with the thiol modified complementary DNA (cDNA), achieving efficient linkage with the nanozyme via Au-S bond. The immobilized nanoenzyme catalyzed the oxidation between 4-chloro-1-naphthol (4-CN) and H₂O₂ to generate insoluble precipitation on the photo-electrode. By virtue of the inhibited PEC signals with the TE-enabled TS extension, an aptasensor for assay of TE activity was developed, showing the wide linear range of 50-5×10⁵ cell mL^-1 and a low detection limit of 19 cell mL^-1. This work provides some valuable guidelines for developing advanced nanozyme-based PEC bioanalysis of diverse cancer cells.

Photoelectrochemical biosensor for CEA detection based on SnS2-GR with multiple quenching effects of Au@CuS-GR

A novel signal on-off type photoelectrochemical (PEC) biosensing system was designed for sensitive detection of carcinoembryonic antigen (CEA) based on tin disulfide nanosheets loaded on reduced graphene cxide (SnS₂-GR) as the photoactive material and gold nanoparticles coated on reduced graphene oxide-functionalized copper sulfide (Au@CuS-GR) for signal amplification. It's the first time for SnS₂-GR was exploited as a sensing matrix. Here, the photocurrent signals of SnS₂ were amplified attributed to the sensitization effect of graphene. As signal amplifier, Au@CuS-GR could quench the photocurrents of SnS₂-GR not only through the p-n type semiconductor quenching effect as well as the steric hindrance effect, but also as peroxidase mimetics to catalyze the oxidation of 4-Chloro-1-naphthol (4-CN) to produce insoluble product on the electrode surface. Based on the multiple signal amplification ability of Au@CuS-GR, CEA was detected sensitively with a linear range from 0.1 pg mL^-1 to 10 ng mL^-1 and limit of detection down to 59.9 fg mL^-1 (S/N = 3). Meanwhile, the PEC biosensor displayed excellent performance in the assay of human serum sample, showing good application prospects for various target analysis.

A dual-model "on-super off" photoelectrochemical/ratiometric electrochemical biosensor for ultrasensitive and accurate detection of microRNA-224

A dual-model "on-super off" photoelectrochemical (PEC)/ratiometric electrochemical (EC) biosensor based on signal enhancing and quenching combining three-dimensional (3D) DNA walker strategy was designed for the ultrasensitive and accurate detection of microRNA-224 (miRNA-224). The "signal on" PEC state was achieved by methylene blue labeled hairpin DNA (MB-DNA) for sensitizing CdS QDs. Then numerous transformational ferrocene labeled DNAs (Fc-DNAs) converted by target-induced 3D DNA walker amplification with the help of Ag nanocubes (NCs) label DNA (Ag-DNA) were introduced to open hairpin MB-DNA. Such configuration change would relocate the sensitizer MB and the quencher Fc, whereas energy transfer placed between Ag NCs and CdS QDs, thereby significantly quenching the PEC signal to obtain "super off" state. Meanwhile, these changes resulted in a decreased oxidation peak current of MB (I_MB) and an increased that of Fc (I_Fc). MiRNA-224 was also detected on basis of the dual-signaling EC ratiometric method for complementary PEC detection. Benefiting from different mechanisms and relatively independent signal transduction, this approach not only avoided interference from difficult assembly but also outstandingly increased sensitivity by distance-controllable signal enhancing and quenching strategies. As a result, the detection ranges of 0.1-1000 fM with a low detection limit of 0.019 fM for PEC, and 0.52 to 500 fM with a low detection limit of 0.061 fM for EC, were obtained for miRNA-224, which opens a new avenue for designing numerous elegant biosensors with potential utility in bioanalysis and early disease diagnosis.

Photoelectrochemical biosensor for protein kinase A detection based on carbon microspheres, peptide functionalized Au-ZIF-8 and TiO2/g-C3N4

In this work, a novel and sensitive photoelectrochemical (PEC) strategy was designed for protein kinase A (PKA) detection, comprising carbon microsphere (CMS) modified ITO electrode, TiO₂ as the phosphate group recognition material and graphite-carbon nitride (g-C₃N₄) as photoactive material. For the first time, gold nanoparticle decorated zeolitic imidazolate frameworks (Au-ZIF-8) was employed to fabricate biosensor for PKA activity assay with the function of substrate peptide immobilization and signal amplification. Firstly, substrate peptides were assembled on the Au-ZIF-8/CMS/ITO surface through the covalent bonding between the gold nanoparticles (AuNPs) and sulfydryl groups of the peptides. Then, in the presence of ATP, phosphorylation of the substrate peptide was achieved under PKA catalysis. Finally, TiO₂-g-C₃N₄ composites were further modified on the electrode surface based on bonding between TiO₂ and phosphate groups created via phosphorylation of the peptide (yielding TiO₂-g-C₃N₄/P-peptide/Au-ZIF-8/CMS/ITO), which is different with our previous work by directly immobilizing g-C₃N₄ composite on electrode surface. The developed method showed a wide linear range from 0.05-50 U mL^-1. The detection limit was 0.02 U mL^-1 (S/N = 3). The constructed biosensor exhibited high detection specificity for PKA. In addition, the wide applicability of this biosensor was demonstrated by evaluating the inhibition ability of ellagic acid towards PKA.

Photoelectrochemical CaMV35S biosensor for discriminating transgenic from non-transgenic soybean based on SiO2@CdTe quantum dots core-shell nanoparticles as signal indicators

A methodology for detection of the Cauliflower Mosaic Virus 35S(CaMV35S) promoter was developed to distinguish transgenic from non-transgenic soybean samples by using photoelectrochemical (PEC) biosensor. In this PEC biosensing system, the as-prepared gold nanoparticles-reduced graphene oxide acted as a nanocarrier to immobilize the thiol-functional probe (probe1), and the SiO₂@CdTe quantum dots (QDs) core-shell nanoparticles tagged with the amino-functional probe (probe2) acted as signal indicators, respectively. In the presence of target DNA (tDNA) of CaMV35S, the binding of tDNA with probe1 and probe2 through the high specific DNA hybridization led to the fabrication of sandwich structure, and thus the high loading of the signal indicators SiO₂@CdTe QDs at the electrode surface, which increased the PEC signal. The increased PEC signal depended on the concentration of tDNA, and a wide linear range from 0.1pM to 0.5nM with low detection limit of 0.05pM was obtained. In addition, the PEC biosensor has been successfully used for discriminating transgenic soybean from non-transgenic samples, which was consistent with the polymerase chain reaction (PCR) results, suggesting the proposed PEC biosensor is a feasible tool for the further daily genetically modified organism detection.

Engineering paper-based visible light-responsive Sn-self doped domed SnO2 nanotubes for ultrasensitive photoelectrochemical sensor

Exploring novel photoactive materials with high photoelectric conversion efficiency plays a crucial role in enhancing the analytical performance of paper-based photoelectrochemical (PEC) biosensor. SnO₂, which possesses higher photostability and electron mobility, can be regarded as a promising photoactive material. Herein, paper-based one dimensional (1D) domed SnO₂ nanotubes (NTs) have been developed with the template-consumption strategy. What's more, their growth mechanism has also been proposed based on the controllable experiments. At first, the paper-based 1D ZnO nanorods (NRs) as the typical amphoteric oxide are prepared and serve as the sacrifice templates which can be etched by the generated alkaline environment during the formation of SnO₂. At a certain stage, all the ZnO NRs can be completely etched by controlling the experimental conditions, resulting in the forming of vertically distributed hollow SnO₂ NTs. Furthermore, the Sn self-doping strategy is also proposed to suppress the recombination of charge carriers and broaden the light response range by introducing the impurity energy levels. Profiting from such doping strategy, the prominent photocurrent signal is obtained compared with pure paper-based SnO₂ NTs. Ultimately, an innovative visible light responsive paper-based Sn-doping SnO_2-x NTs are developed and employed as the photoelectrode for the PEC biosensor using the alpha fetoprotein (AFP) as the model analyte. Under the optimal conditions, the ultrasensitive AFP sensing is realized with the linear range and detection limitation of 10 pg mL^-1 to 200 ng mL^-1 and 3.84 pg mL^-1, respectively. This work provides a judiciously strategy for developing novel photoactive materials for paper-based PEC bioanalysis.

Preparation of PbS NPs/RGO/NiO nanosheet arrays heterostructure: Function-switchable self-powered photoelectrochemical biosensor for H2O2 and glucose monitoring

On the basis of synthesized PbS nanoparticles (PbS NPs)/reduced graphene oxide (RGO)/NiO nanosheet arrays (NiO NSAs) heterostructure, we constructed a function-switchable self-powered PEC sensing platform for the analysis of H2O2 and glucose. Ordered NiO NSAs have high electron mobility, modifying RGO onto the surfaces of NiO NSAs can connect the NiO NSAs with the PbS NPs and promoted the electron transfer rate between them, as well as enhance their photocurrent response. The PbS NPs/RGO/NiO NSAs heterostructure own excellent catalase-like activity can achieve H2O2 detection, only with one more step, after introducing glucose oxidase (GOD) onto the surface of PbS NPs/RGO/NiO NSAs heterostructure, we realized the detection conversion between H2O2 and glucose. Under optimal conditions, the proposed biosensor exhibited superior analytical performance toward H2O2 and glucose, a limit of detection (LOD) of 0.018 mM (S/N = 3) and 5.3 × 10-8 M (S/N = 3) were obtained, respectively. Moreover, good accuracy was obtained in the real samples analysis of H2O2 disinfectant and human serum samples.

Rolling circle amplification promoted magneto-controlled photoelectrochemical biosensor for organophosphorus pesticides based on dissolution of core-shell MnO2 nanoflower@CdS mediated by butyrylcholinesterase

A photoelectrochemical (PEC) aptasensing platform is devised for sensitive detection of an organophosphorus pesticide based on dissolution of core-shell MnO₂ nanoflower@CdS (MnO₂ NF@CdS) by thiocholine (TCh). TCH is produced from the butyrylcholinesterase-acetylthiocholine system, accompanied by target-triggered rolling circle amplification (RCA). The core-shell MnO₂ NF@CdS with excellent PEC performance was synthesized and employed as a photo-sensing platform. The target was detected on a functionalized magnetic probe with the corresponding aptamer. Upon malathion introduction, the aptamer was detached from the magnetic beads, while capture DNA (cDNA, with primer fragment) remained on the beads. The primer fragment in cDNA can trigger the RCA reaction to form a long single-stranded DNA (ssDNA). Furthermore, a large number of butyrylcholinesterase (BChE) were assembled on the long ssDNA strands through the hybridization with the S₂-Au-BChE probe. Thereafter, TCh generated from hydrolysis of ATCh by BChE can reduce MnO₂ NF (core) to Mn²⁺ and release the CdS nanoparticles (shell) from the platform electrode, significantly enhancing the PEC signal. Under optimal conditions, the proposed aptasensor exhibited high sensitivity for malathion with a low detection limit of 0.68 pg mL^-1. Meanwhile, it also presents outstanding specificity, reproducibility, and stability. Importantly, the sensing platform provides a new concept for detection of pesticide. Graphical abstract Herein, this work devised a photoelectrochemical (PEC) aptasensing platform for sensitive detection of organophosphorus pesticide based on dissolution of core-shell MnO₂ nanoflower@CdS (MnO₂ NF@CdS) by the as-produced thiocholine (TCh) from the butyrylcholinesterase-acetylthiocholine system, accompanying with the target-triggered rolling circle amplification (RCA).

MoS2@Ti3C2 nanohybrid-based photoelectrochemical biosensor: A platform for ultrasensitive detection of cancer biomarker exosomal miRNA

As a class of newly identified biomarkers, miRNAs show enormous potential in cancer diagnosis. The sensitive detection of abnormal miRNAs concentration to realize early diagnosis of malignant tumors is a frontier in the field of biosensing. In this work, a photoelectrochemical (PEC) biosensor based on MoS₂@Ti₃C₂ nanohybrid was fabricated for the ultrasensitive detection of miRNAs. The hybridization of Ti₃C₂ with excellent electron transfer capability significantly enhances the photocurrent response of the PEC biosensor. Moreover, the electrodeposition of Au nanoparticles on the surface of MoS₂@Ti₃C₂ nanohybrid further enhances the photocurrent. The detection performance of the PEC biosensor has been tested using colorectal cancer-related exosomal miRNA (miR-92a-3p) as the target. The PEC biosensor shows a broad linear detection ranged from 1 fM to 100 nM and a calculated detection limit of 0.27 fM. In terms of selectivity, the PEC biosensor can distinguish miR-92a-3p from mismatched sequences. The 16 continuous radiation source on-off cycles test indicates the high stability of the PEC biosensor. Furthermore, the accurate detection of exosomal miR-92a-3p concentrations of patients and healthy controls demonstrates the clinical feasibility of the PEC biosensor. Based on these outcomes, the PEC biosensor exhibits the prospect of realizing the ultrasensitive point-of-care detection of miRNAs.

A photoelectrochemical biosensor for rapid and ultrasensitive norovirus detection

The highly contagious norovirus (NoV) is the most common causative agent of acute gastroenteritis, resulting in >200,000 deaths worldwide annually. A rapid and sensitive detection method is a prerequisite for effective prevention and timely identification of NoV contamination. In the present study, we developed a photoelectrochemical (PEC) biosensor coupled with a novel custom-made monoclonal antibody (mAb) for specific and sensitive NoV detection. Our system could detect levels of recombinant NoV capsid protein VP1 as low as 2 × 10^-10 g mL^-1 (4.9 pM) within 30 min in a concentration-dependent manner. More importantly, the biosensor was versatile in detecting virus isolated from real samples that were as low as 46 copies μL^-1. These findings indicate that this system has the potential to serve as a convenient point-of-care system for diagnosing NoV infection and detecting NoV-contaminated food samples.

Hollow SnO2/CdS QDs/CdCO3 heterostructured nanocubes coupled with hollow PtPd/MnCo-CeO2 nanozyme-mediated synergistic amplification for ultrasensitive PEC immunoanalysis of lung cancer biomarker

Nowadays, lung cancer is one of the most dangerous cancers threatening human life all over the world. As a crucial biomarker, cytokeratin 19 fragment 21-1 (CYFRA 21-1) is extraordinary important for diagnosis of non-small cell lung cancer (NSCLC). In this work, we synthesized hollow SnO₂/CdS QDs/CdCO₃ heterostructured nanocubes with high and stable photocurrents, which applied to construction of a sandwich-typed photoelectrochemical (PEC) immunosensor for detection of CYFRA 21-1, integrated by in-situ catalytic precipitation strategy with home-built PtPd alloy anchored MnCo-CeO₂ (PtPd/MnCo-CeO₂) nanozyme for synergistic amplification. The interfacial electron transfer mechanism upon visible-light irradiation was investigated in details. Further, the PEC responses were seriously quenched by the specific immunoreaction and precipitation catalyzed by the PtPd/MnCo-CeO₂ nanozyme. The established biosensor showed a wider linear range of 0.001-200 ng mL^-1 and a lower limit of detection (LOD = 0.2 pg mL^-1, S/N = 3), coupled by exploring such analysis even in diluted human serum sample. This work opens a constructive avenue to develop ultrasensitive PEC sensing platforms for detecting diverse cancer biomarkers in clinic.

Z-scheme Bi2O3/CuBi2O4 heterojunction enabled sensitive photoelectrochemical detection of aflatoxin B1 for health care, the environment, and food

Designing a photoelectrochemical (PEC) biosensor with preponderant sensitivity and anti-interference is a challenge for detecting small molecules in real samples with complex matrices. To this end, the Bi₂O₃/CuBi₂O₄ was synthesized in one step to enhance visible light's absorption ability, transferring the interfacial carrier's efficiency, a high-active Z-scheme heterojunction, and a photocathode biosensor was proposed. For the first time, we used the density functional theory to verify a Z-scheme transfer pathway of photogenerated electrons in Bi₂O₃/CuBi₂O₄ and the energy band structure of Bi₂O₃ and CuBi₂O₄, respectively. Bi₂O₃/CuBi₂O₄-based PEC biosensor was developed for competive immunoassay of small molecular, aflatoxin B1 (AFB1) as an example, resulting in a low detection limit of 297.4 fg/mL and a linear range of 1.4 pg/mL-280 ng/mL in urine, water, peanut, and wheat samples. Using spiked experiments, the satisfied repeatability, reproducibility, stability, and specificity of the Bi₂O₃/CuBi₂O₄-based PEC biosensor indicated a promise for application in health care, the environment, and food.

Enhanced photoelectrochemical detection of bioaffinity reactions by vertically oriented au nanobranches complexed with a biotinylated polythiophene derivative

Four nanostructured Au electrodes were prepared by a simple and templateless electrochemical deposition technique. After complexing with a biotinylated polythiophene derivative (PTBL), photocurrent generation and performance of PTBL/Au-nanostructured electrodes as photoelectrochemical biosensors were investigated. Among these four nanostructured Au electrodes, vertically oriented nanobranches on the electrode significantly improved the photoelectric conversion, because the vertically oriented nanostructures not only benefit light harvesting but also the transfer of the photogenerated charge carriers. Owing to this advantaged nanostructure, the PTBL/Au-nanobranch electrode showed higher sensitivity and faster response times in the photoelectrochemical detection of a streptavidin-biotin affinity reaction compared to a PTBL/Au-nanoparticle electrode.

MXene Enhanced Photoactivity of Bi2O3/Bi2S3 Heterojunction with G-wire Superstructure for Photoelectrochemical Detection of TET1 Protein

Ten-eleven translocation 1 (TET1) protein has the potential to accelerate the oxygenation of 5-methylcytosine to 5-hydroxymethylcytosine (5hmC); then the -CH₂OH of 5hmC can further covalently react with -SH catalyzed by M.HhaI methyltransferase. A brand-new photoelectrochemical (PEC) detection technique for the TET1 protein was created in light of this. For this objective, the Bi₂O₃/Bi₂S₃ heterojunction was first prepared by a one-pot hydrothermal method and served for photosensitive materials. For further enhancing the photoactivity, Bi₂O₃/Bi₂S₃ was blended with MXene to form an energy band-matched structure, thus improving the migration kinetics of photogenerated carriers. For achieving a high sensitivity of detection, a DNA Walker incorporated with the nicking endonuclease (Nb.BbvCI enzyme)-assisted signal amplification strategy was presented to output exponential G-quadruplex fragments. Self-assembly of the free G-quadruplex sequence into a G-wire superstructure with the assistance of Mg²⁺ provided more loading sites for MB and amplified the PEC signal. The linear range of the biosensor was 0.1-10 μg/mL with a detection limit of 0.024 μg/mL (S/N = 3) for TET1 protein under optimal experimental conditions. The suitability of the proposed method was evaluated by inhibitor screening experiments and the influence of environmental degradation on the activity of TET1 protein.

Near-infrared light-induced photoelectrochemical biosensor based on plasmon-enhanced upconversion nanocomposites for microRNA-155 detection with cascade amplifications

Herein, a novel near-infrared (NIR) light-driven photoelectrochemical (PEC) biosensor based on NaYF₄:Yb³⁺, Er³⁺@Bi₂MoO₆@Bi (NYF@BMO@Bi) nanocomposites was elaborately developed to achieve highly sensitive detection of microRNA-155 (miRNA-155). To realize signal enhancement, the coupled plasmonic bismuth (Bi) nanoparticles were constructed as an energy relay to facilitate the transfer of energy from NaYF₄:Yb³⁺, Er³⁺ to Bi₂MoO₆, ultimately enabling the efficient separation of electron-hole pairs of Bi₂MoO₆ under the irradiation of a 980 nm laser. For constructing biosensing system, the initial signal was firstly amplified after the addition of alkaline phosphatase (ALP) in conjunction with the biofunctionalized NYF@BMO@Bi nanocomposites, which could catalyze the conversion of ascorbic acid 2-phosphate into ascorbic acid, and then consumed the photoacoustic holes created on the surface of Bi₂MoO₆ for the enlarging photocurrent production. Upon addition of target miRNA-155, the cascade signal amplification process was triggered while the ALP-modified DNA sequence was replaced and then followed by the initiation of a simulated biocatalytic precipitation reaction to attenuate the photocurrent response. On account of the NIR-light-driven and cascade amplifications strategy, the as-constructed biosensor was successfully utilized for the accurate determination of miRNA-155 ranging from 1 fM to 0.1 μM with a detection limit of 0.32 fM. We believed that the proposed nanocomposites-based NIR-triggered PEC biosensor could provide a promising platform for effective monitoring other tumor biomarkers in clinical diagnostics.

Hollow cage-like PtCu nanozyme-regulated photo-activity of porous CdIn2S4/SnO2 heterojunctions for ultrasensitive PEC sensing of streptomycin

Streptomycin (STR) is extensively employed for preventive and curative purposes in animals, which is accumulated in human body through food chain and induces serious health problems. Herein, highly photoactive type II heterojunctions of porous CdIn₂S₄/SnO₂ microspheres were initially prepared, which can effectively inhibit the recombination of the charge-hole pairs. Besides, the peroxidase-mimicking catalytic property of the hollow PtCu nanocages (PtCu NCs) was carefully investigated by UV-vis spectroscopy, where catalytic oxidation of tetramethylbenzidine behaved as the benchmarked reaction. On such basis, a highly selective photoelectrochemical (PEC) aptasensor was established with the CdIn₂S₄/SnO₂ heterojunctions for bioanalysis of streptomycin, coupled by the PtCu NCs nanozyme-catalyzed biocatalytic precipitation to achieve signal magnification. Specifically, the home-made nanozyme was applied for catalytic oxidation of 3,3'-diaminobenzidine to generate insulating precipitate in aqueous H₂O₂ system and thereby block the light harvesting on the photoanode, showing steeply declined PEC responses. The as-built aptasensor showed a broad linear range of 0.01-200 nM with a low limit of detection of 7.50 pM (S/N = 3) for such analysis, combined by exploring its practical detection in milk samples. This work shows excellent nanozyme-catalyzed signal amplification for fabrication of ultrasensitive PEC biosensors towards other antibiotics detection.