Modulating Polarization of Perovskite-Based Heterostructures via In Situ Semiconductor Generation and Enzyme Catalysis for Signal-Switchable Photoelectrochemical Biosensing

Flexible Multimodal Sensors Enhanced by Electrospun Lead-Free Perovskite and PVDF-HFP Composite Form-Stable Mesh Membranes for In Situ Plant Monitoring

The pH and humidity of the crop environment are essential indicators for monitoring crop growth status. This study reports a lead-free perovskite/polyvinylidene fluoride-hexafluoropropylene composite (LPPC) to enhance the stability and reliability of in situ plant pH and humidity monitoring. The mesh composite membrane of LPPC illustrates a hydrophobic contact angle of 101.982°, a tensile strain of 800%, and an opposing surface potential of less than -184.9 mV, which ensures fast response, high sensitivity, and stability of the sensor during long-term plant monitoring. The LPPC-coated pH electrode possesses a sensitivity of -63.90 mV/pH, which provides a fast response within 5 s and is inert to environmental temperature interference. The LPPC-coated humidity sensor obtains a sensitivity of -145.7 Ω/% RH, responds in 28 s, and works well under varying light conditions. The flexible multimodal sensor coated with an LPPC membrane completed real-time in situ monitoring of soilless strawberries for 17 consecutive days. Satisfactory consistency and accuracy performance are observed. The study provides a simple solution for developing reliable, flexible wearable multiparameter sensors for in situ monitoring of multiple parameters of crop environments.

Multifunctional Supramolecular Hydrogel Modulated Heterojunction Interface Carrier Transport Engineering Facilitates Sensitive Photoelectrochemical Immunosensing

Highly responsive interface of semiconductor nanophotoelectrochemical materials provides a broad development prospect for the identification of low-abundance cancer marker molecules. This work innovatively proposes an efficient blank WO3/SnIn4S8 heterojunction interface formed by self-assembly on the working electrode for interface regulation and photoregulation. Different from the traditional biomolecular layered interface, a hydrogel layer containing manganese dioxide with a wide light absorption range is formed at the interface after an accurate response to external immune recognition. The formation of the hydrogel layer hinders the effective contact between the heterojunction interface and the electrolyte solution, and manganese dioxide in the hydrogel layer forms a strong competition between the light source and the substrate photoelectric material. The process effectively improves the carrier recombination efficiency at the interface, reduces the interface reaction kinetics and photoelectric conversion efficiency, and thus provides strong support for target identification. Taking advantage of the process, the resulting biosensors are being explored for sensitive detection of human epidermal growth factor receptor 2, with a limit of detection as low as 0.037 pg/mL. Also, this study contributes to the advancement of photoelectrochemical biosensing technology and opens up new avenues for the development of sensitive and accurate analytical tools in the field of bioanalysis.

Ti3C2@UiO-TCPP Schottky junction photoelectrochemical sensor for detecting alkaline phosphatase through the steric hindrance effect of phosphopeptide

Alkaline phosphatase (ALP) is a major biomarker for clinical diagnosis, but detection methods of ALP are limited in sensitivity and selectivity. In this paper, a novel method for ALP determination is proposed. A photoelectrochemical (PEC) sensor was prepared by growing UiO-tetratopic tetrakis (4-carbox-yphenyl) porphyrin (TCPP) in situ between layered Ti3C2 through a one-pot hydrothermal method. The obtained Schottky heterojunction photoelectric material Ti3C2@UiO-TCPP not only has a large light absorption range but also greatly improves the efficiency of photogenerated electron hole separation and thereby enhances sensitivity for PEC detection. The phosphate group on the phosphorylated polypeptide was utilized to form a Zr-O-P bond with the zirconium ion on UiO-66, and then photocurrent decreases due to the steric hindrance effect of phosphorylated polypeptides, that is, the hindrance of electron transfer between the photoelectric material and a solution. The specific interaction between ALP and phosphorylated polypeptides shears the bond between phosphate and zirconium ion on UiO-66 in the peptides then weakens the hindrance effect and increases the photocurrent, thus realizing ALP detection. The linear range of ALP is 0.03-10,000 U·L-1, and the detection limit is 0.012 U·L-1. The method is highly sensitive and selective, and has been applied in detection of ALP in serum samples.

Polarity Conversion of the Ag2S/AgInS2 Heterojunction by Radical-Induced Positive Feedback Polydopamine Adhesion for Signal-Switchable Photoelectrochemical Biosensing

Efficient tuning of the polarity of photoactive nanomaterials is of great importance in improving the performance of photoelectrochemical (PEC) sensing platforms. Herein, polarity of the Ag2S/AgInS2 heterojunction is converted by radical-induced positive feedback polydopamine (PDA) adhesion, which is further employed to develop a signal-switchable PEC biosensor. In the nanocomposites, Ag2S and AgInS2 achieve electron-hole separation, exhibiting a strong anodic PEC response. Under the irradiation of light, the Ag2S/AgInS2 heterojunction is able to produce superoxide radical and hydroxyl radical intermediate species, leading to the polymerization of dopamine (DA) and the subsequent adhesion of PDA onto the Ag2S/AgInS2 heterojunction (Ag2S/AgInS2@PDA). By constructing a new electron-transfer pathway with PDA, the polarity of the Ag2S/AgInS2 heterojunction is converted, and the PEC response changes from anodic to cathodic photocurrents. In addition, since the photoreduction activity of PDA is stronger than that of the Ag2S/AgInS2 heterojunction, more superoxide radical can be produced by Ag2S/AgInS2@PDA once PDA is generated, thereby promoting the generation of PDA. Consequently, a positive feedback mechanism is established to enhance the polarity conversion of the Ag2S/AgInS2 heterojunction and amplify the responding to DA. As a result, the bioanalytical method is capable of sensitively quantifying DA in 10 orders of magnitude with an ultralow limit of detection. Moreover, the applicability of this biosensor in real samples is identified by measuring DA in fetal bovine serum and compared with a commercial ELISA method. Overall, this work offers an alternative perspective for adjusting photogenerated carriers of nanomaterials and designing high-performance PEC biosensors.

A Direct-Contact Photocurrent-Direction-Switching Biosensing Platform Based on In Situ Formation of CN QDs/TiO2 Nanodiscs and Double-Supported 3D DNA Walking Amplification

Herein, a direct-contact photocurrent-direction-switching photoelectrochemical (PEC) biosensing platform for the ultrasensitive and selective detection of soluble CD146 (sCD146) is reported for the first time via in situ formation of carbon nitride quantum dots (CN QDs)/titanium dioxide (TiO2 ) nanodiscs with the double-supported 3D DNA walking amplification. In this platform, metal organic frameworks (MOFs)-derived porous TiO2 nanodiscs exhibit excellent anodic photocurrent, whereas a single-stranded auxiliary DNA (ssDNA) as biogate is absorbed onto the TiO2 nanodiscs to block active sites. Subsequently, with the help of intermediate DNAs from target sCD146-induced double-supported 3D DNA walking signal amplification, the ssDNA can leave away from the surface of TiO2 nanodiscs due to the specific hybridization with intermediate DNAs. Afterward, the successful direct contact of CN QDs on TiO2 nanodiscs by porosity and electrostatic adsorption, leads to the effective photocurrent-direction switching from anodic to cathodic photocurrent. Based on direct-contact photocurrent-direction-switching CN QDs/TiO2 nanodiscs system and double-supported 3D DNA walking signal amplification, sCD146 is detected sensitively with a wide linear range (10 fg mL-1 to 5 ng mL-1 ) and a low limit of detection (2.1 fg mL-1 ). Also, the environmentally friendly and direct-contact photocurrent-direction-switching PEC biosensor has an application prospect for cancer biomarker detection.

Carbon Nitride-Based Heterojunction Photoelectrodes with Modulable Charge-Transfer Pathways toward Selective Biosensing

Photoelectrochemical (PEC) sensing enables the rapid, accurate, and highly sensitive detection of biologically important chemicals. However, achieving high selectivity without external biological elements remains a challenge because the PEC reactions inherently have poor selectivity. Herein, we report a strategy to address this problem by regulating the charge-transfer pathways using polymeric carbon nitride (pCN)-based heterojunction photoelectrodes. Interestingly, because of redox reactions at different semiconductor/electrolyte interfaces with specific charge-transfer pathways, each analyte demonstrated a unique combination of photocurrent-change polarity. Based on this principle, a pCN-based PEC sensor for the highly selective sensing of ascorbic acid in serum against typical interferences, such as dopamine, glutathione, epinephrine, and citric acid was successfully developed. This study sheds light on a general PEC sensing strategy with high selectivity without biorecognition units by engineering charge-transfer pathways in heterojunctions on photoelectrodes.

Inspired by game theory: Multi-signal output photoelectrochemical point-of-care immunoassay based on target-triggered organic electronic barriers

This work presents an integrated photoelectrochemical, impedance and colorimetric biosensing platform for flexible detection of cancer markers based on the targeted response by combining liposome amplification strategies and target-induced non-in situ formation of electronic barriers as the signal transduction modality on carbon-modified CdS photoanodes. Inspired by game theory, the carbon layer modified CdS hyperbranched structure with low impedance and high photocurrent response was firstly obtained by surface modification of CdS nanomaterials. Through a liposome-mediated enzymatic reaction amplification strategy, a large number of organic electron barriers were formed by a biocatalytic precipitation (BCP) reaction triggered by horseradish peroxidase released from cleaved liposomes after the introduction of the target molecule, thereby increasing the impedance characteristics of the photoanode as well as attenuating the photocurrent. The BCP reaction in the microplate was accompanied by a significant color change, which opened up a new window for point-of-care testing. Taking carcinoembryonic antigen (CEA) as a proof of concept, the multi-signal output sensing platform showed a satisfactory sensitive response to CEA with an optimal linear range of 20 pg mL^-1-100 ng mL^-1. The detection limit was as low as 8.4 pg mL^-1. Meanwhile, with the assistance of a portable smartphone and a miniature electrochemical workstation, the electrical signal obtained was synchronized with the colorimetric signal to correct the actual target concentration in the sample, further reducing the occurrence of false reports. Importantly, this protocol provides a new idea for the sensitive detection of cancer markers and the construction of a multi-signal output platform.

Bio-inspired nanozyme with ultra-thin Fe-Bi2O2S nanosheets for in-situ amplified photoelectrochemical immunoassay of cancer-related protein

A Fe-loaded Bi₂O₂S nanosheet photoanode serving as photoelectric biomonitoring platform for the detection of prostate-specific antigen (PSA) using biologically inspired prussian nanoparticle (PB)-catalyzed biocatalytic precipitation strategy was developed. Primarily, the signal probe PB-mAb₂ obtained by electrostatic adsorption was immobilized on a microplate in the presence of target PSA, and 4-chloro-1-naphthol (4-CN) was oxidized to benzo-4-chloro-hexadienone (4-CD) with the assistance of exogenous hydrogen peroxide, which was generated by a large number of hydroxyl radicals catalyzed by PB. The generated 4-CD showed strongly low conductivity characteristics to burst the photocurrent of highly photoactive Fe-Bi₂O₂S photoanode. The split incubation reaction could be suitable for high volume and low-cost rapid detection. A dynamic response range of 0.1-100 ng mL^-1 with a limit of detection of 34.2 pg mL^-1 was achieved with the sensor based on a photoelectric sensing platform and a biomimetic catalytic precipitation reaction. Equally important, the sensor also showed good potential in the detection of real samples compared to commercially available ELISA kits. In conclusion, this work provides a fresh scheme for the development of sensitive biosensors through a bio-inspired catalytic strategy of versatility and a photoanode coupling with high photoelectric activity.

Integrated solar-powered MEMS-based photoelectrochemical immunoassay for point-of-care testing of cTnI protein

Considering the fact that acute myocardial infarction has shown a trend towards younger age and has become a major health problem, it is necessary to develop rapid screening devices to meet the needs of community health care. Herein, we developed an artificial neural network-assisted solar-powered photoelectrochemical (SP-PEC) sensing platform for rapid screening of cardiac troponin I (cTnI) protein in the prognosis of patients with acute myocardial infarction (AMI) by integrating a self-powered photoelectric signal output system with low-cost screen-printed paper electrodes functionalized with ultrathin Bi₂O₂S (BOS) nanosheets. An integrated solar-powered PEC immunoassay with micro-electro-mechanical system (MEMS) was constructed without an excitation light source. The quantification of cTnI protein was obtained by the electrical signal changes caused by the electro-oxidation process of H₂O₂, generated by the classical split immune reaction, on the electrode surface. The test electrodes were developed as dual working electrodes, one for target cTnI testing and the other for evaluating light intensity, to reduce the temporal inconsistency of sunlight. The photoelectrodes were discovered to exhibit satisfactory negative response to target concentrations in the dynamic range of 2.0 pg mL^-1-10 ng mL^-1 since being regressed in an improved artificial neural network (ANN) model using the pooled dataset of target signals affected by the light source. The difference of hot electron and hole transfer behavior in different thickness of nano-materials was determined by finite element analysis (FEA), which provided a theoretical basis for the development of efficient PEC sensors. This work presents a unique perspective for the design of a revolutionary low-cost bioassay platform by inventively illuminating the PEC biosensor's component process without the use of light.

In Situ Growth of Cs3Bi2Br9 Quantum Dots on Bi-MOF Nanosheets via Cosharing Bismuth Atoms for CO2 Capture and Photocatalytic Reduction

Given the global warming caused by excess CO₂ accumulation in the atmosphere, it is essential to reduce CO₂ by capturing and converting it to chemical feedstock using solar energy. Herein, a novel Cs₃Bi₂Br₉/bismuth-based metal-organic framework (Bi-MOF) composite was prepared via an in situ growth strategy of Cs₃Bi₂Br₉ quantum dots (QDs) on the surface of Bi-MOF nanosheets through coshared bismuth atoms. The prepared Cs₃Bi₂Br₉/Bi-MOF exhibits bifunctional merits for both the high capture and effective conversion of CO₂, among which the optimized 3Cs₃Bi₂Br₉/Bi-MOF sample shows a CO₂-CO conversion yield as high as 572.24 μmol g^-1 h^-1 under the irradiation of a 300 W Xe lamp. In addition, the composite shows good stability after five recycles in humid air, and the CO₂ photoreduction efficiency does not decrease significantly. The mechanistic investigation uncovers that the intimate atomic-level contact between Cs₃Bi₂Br₉ and Bi-MOF via the coshared atoms not only improves the dispersion of Cs₃Bi₂Br₉ QDs over Bi-MOF nanosheets but also accelerates interfacial charge transfer by forming a strong bonding linkage, which endows it with the best performance of CO₂ photoreduction. Our new finding of bismuth-based metal-organic framework/lead-free halide perovskite by cosharing atoms opens a new avenue for a novel preparation strategy of the heterojunction with atomic-level contact and potential applications in capture and photocatalytic conversion of CO₂.

Novel Aggregation-Enhanced PEC Photosensitizer Based on Electrostatic Linkage of Ionic Liquid with Protoporphyrin IX for Ultrasensitive Detection of Molt-4 Cells

Nowadays, aggregation quenching of most organic photosensitizers in aqueous media seriously restricts analytical and biomedical applications of photoelectrochemical (PEC) sensors. In this work, an aggregation-enhanced PEC photosensitizer was prepared by electrostatically bonding protoporphyrin IX (PPIX) with an ionic liquid of 1-butyl-3-methylimidazole tetrafluoroborate ([BMIm][BF₄]), termed as PPIX-[BMIm] for clarity. The resultant PPIX-[BMIm] showed weak photocurrent in pure dimethyl sulfoxide (DMSO, good solvent), while the PEC signals displayed a 44.1-fold enhancement in a water (poor solvent)/DMSO binary solvent with a water fraction (f_w) of 90%. Such PEC-enhanced mechanism was critically studied by electrochemistry and density functional theory (DFT) calculation in some detail. Afterward, a label-free PEC cytosensor was built for ultrasensitive bioassay of acute lymphoblastic leukemia (molt-4) cells by electrodepositing Au nanoparticles (Au NPs) on the PPIX-[BMIm] aggregates and sequential assembly of protein tyrosine kinase (PTK) aptamer DNA (aptDNA). The resultant cytosensor showed a wide linear range (300 to 3 × 10⁵ cells mL^-1) with a limit of detection (LOD) as low as 63 cells mL^-1. The aggregation-enhanced PEC performance offers a valuable and practical pathway for synthesis of advanced organic photosensitizer to explore its PEC applications in early diagnosis of tumors.

Highly Selective Photoelectrochemical Assay of Arsenate Based on Magnetic Co3O4-Fe3O4 Cubes and the Negative-Background Signal Strategy

Water pollution presents a significant environmental concern on earth. Herein, due to the serious environmental harmfulness of arsenate [As(V)], an iron phthalocyanine (FePc)-induced switchable photocurrent-polarity platform was developed for highly selective assay of As(V). First, magnetic Co₃O₄-Fe₃O₄ cubes were obtained by calcination of the CoFe Prussian blue analogue and then functionalized with oligonucleotide (S1). In the presence of As(V), S1 could be released based on the stronger affinity between As(V) and Co₃O₄-Fe₃O₄ cubes. After magnetic separation by Co₃O₄-Fe₃O₄ cubes, the released S1 was used to trigger the catalytic hairpin assembly (CHA) and hybridization chain reaction, resulting in the formation of lots of G-quadruplex structures on the AgInS₂/ITO electrode. Then, the capture of FePc by the G-quadruplex led to the switch of the photocurrent polarity of the AgInS₂/ITO electrode from the anode to the cathode. Thus, As(V) was sensitively assayed with a low detection limit of 1.0 nM and a wide linear response range from 10 nM to 200 μM. This meets the detection requirement of the World Health Organization for the arsenic concentration in drinking water [less than 10 μg L^-1 (130 nM)]. In addition, whether it was cationic or anionic interferents except phosphate (PO₄^3-), only As(V) could generate the cathodic photocurrent, effectively avoiding the false-positive or false-negative results during As(V) assay. Interestingly, As(V) was also simultaneously separated from the detection system by Co₃O₄-Fe₃O₄ magnetic cubes. The proposed photoelectrochemical platform may have a great potential application for the selective detection of As(V) in environmental fields.

Photo-Assisted Robust Anti-Interference Self-Powered Biosensing of MicroRNA Based on Pt-S Bonds and the Inorganic-Organic Hybridization Strategy

Photo-assisted biofuel cell-based self-powered biosensors (PBFC-SPBs) possess the advantages of no need for external power supply, ease of sensing design, and simple instruments. In this work, a robust anti-interference PBFC-SPB for microRNA detection was constructed based on the Pt-S bond and the inorganic-organic hybridization strategy. The organic semiconductor [6,6]-phenyl-C61-butyric acid methylester@anthraquinone (PCBM@anthraquinone) served as an efficient light-harvesting material, and gold nanoparticle@Pt (AuNP@Pt) nanomaterials were immobilized on the surface via electrostatic adsorption for the binding of DNA. Notably, compared to Au-S bonds for DNA immobilization, the Pt-S bond exhibited better anti-interference ability. Ingeniously, cadmium sulfide quantum dots (CdS QDs) were close to the PCBM@anthraquinone substrate electrode to form sensitization structures, which was beneficial to enhance the photocurrent signal. Combining with the laccase-mimicking activity Cu²⁺/carbon nanotubes (Cu²⁺/CNTs) cathode, the PBFC-SPB for microRNA detection was achieved. Once the target existed, the identical sequence complementary microRNA would make DNA2/CdS dissociate and break away from the electrode, leading to a low signal. The linear detection range was 10 fM-100 pM, with the limit of determination of 2.4 fM (3S/N). The as-proposed strategy not only paves a new way for the design of photoelectrochemical biosensing but also opens a door for the construction of robust anti-interference bioassay for microRNA detection.

A Target-Driven Self-Feedback Paper-Based Photoelectrochemical Sensing Platform for Ultrasensitive Detection of Ochratoxin A with an In2S3/WO3 Heterojunction Structure

Currently, developing versatile, easy-to-operate, and effective signal amplification strategies hold great promise in photoelectrochemical (PEC) biosensing. Herein, an ultrasensitive polyvinylpyrrolidone-treated In₂S₃/WO₃ (In₂S₃-P/WO₃)-functionalized paper-based PEC sensor was established for sensing ochratoxin A (OTA) based on a target-driven self-feedback (TDSF) mechanism enabled by a dual cycling tactic of PEC chemical-chemical (PECCC) redox and exonuclease III (Exo III)-assisted complementary DNA. The In₂S₃-P/WO₃ heterojunction structure with 3D open-structure and regulable topology was initially in situ grown on Au nanoparticle-functionalized cellulose paper, which was served as a universal signal transducer to directly record photocurrent signals without complicated electrode modification, endowing the paper chip with admirable anti-interference ability and unexceptionable photoelectric conversion efficiency. With the assistance of Exo III-assisted cycling process, a trace amount of OTA could trigger substantial signal reporter ascorbic acid (AA) generated by the enzymatic catalysis of alkaline phosphatase, which could effectively provoke the PECCC redox cycling among the tris(2-carboxyethyl)phosphine acid, AA, and ferrocenecarboxylic at the In₂S₃-P/WO₃ photoelectrode, initiating TDSF signal amplification. Based on the TDSF process induced by the Exo III-assisted recycling and PECCC redox cycling strategy, the developed paper-based PEC biosensor realized ultrasensitive determination of OTA with persuasive selectivity, high stability, and excellent reproducibility. It is believed that the proposed paper-based PEC sensing platform exhibited enormous potential for the detection of other targets in bioanalysis and clinical diagnosis.

A signal-off photoelectrochemical aptasensor for ultrasensitive 17β-estradiol detection based on rose-like CdS@C nanostructure and enzymatic amplification

Carbon-coated cadmium sulfide rose-like nanostructures (CdS@C NRs) were prepared via a facile solvothermal approach and used as the photoelectrochemical (PEC) sensing platform for the integration of functional biomolecules. Based on this, a novel "signal-off" PEC aptasensor mediated by enzymatic amplification was proposed for the sensitive and selective detection of 17β-estradiol (E2). In the presence of E2, alkaline phosphatase-modified aptamer (ALP-apta) were released from the electrode surface through the specific recognition with E2, which caused the negative effect on PEC response due to the decrease of ascorbic acid (AA) produced by the ALP in situ enzymatic catalysis. The developed PEC aptasensor for detection of E2 exhibited a wide linear range of 1.0-250 nM, with the low detection limit of 0.37 nM. This work provides novel insight into the design of potential phoelectroactive materials and the application of signal amplification strategy in environmental analysis field.

Recent advances in electron manipulation of nanomaterials for photoelectrochemical biosensors

This feature article discusses the recent advances and strategies of building photoelectrochemical (PEC) biosensors from the perspective of regulating the electron transfer of nanomaterials.

AgCu@CuO aerogels with peroxidase-like activities and photoelectric responses for sensitive biosensing

Photoelectrochemical (PEC) enzymatic biosensors integrate the excellent selectivity of enzymes and high sensitivity of PEC bioanalysis, but the drawbacks such as high cost, poor stability, and tedious immobilization of natural enzymes on photoelectrodes severely suppress their applications. AgCu@CuO aerogel-based photoelectrode materials with both remarkable enzyme-like activities and outstanding photoelectric properties were innovatively designed and synthesized to evaluate the activity of xanthine oxidase with a wide linear detection range and a low limit of detection.

Photoelectrochemical immunoassay of interleukin-6 based on covalent reaction-triggered photocurrent polarity switching of ZnO@fullerenol

We report here a novel photocurrent polarity switching strategy for a photoelectrochemical immunoassay driven by the covalent reaction between fullerenol (COH) and chloranilic acid (CA). The sensitive detection of interleukin-6 is achieved by using CA-encapsulated liposome as the label and COH-coated ZnO as the photoactive material, with a detection limit of 1.0 fg mL^-1.

A photocurrent-polarity-switching biosensor for highly selective assay of mucin 1 based on target-induced hemin transfer from ZrO2 hollow spheres to G-quadruplex nanowires

Herein, a photocurrent polarity switching platform for highly selective assay of mucin 1 (MUC1) was developed based on target-induced hemin transfer from ZrO₂ hollow spheres (ZrO₂ HSs) to G-quadruplex nanowires (G wires). In this system, SiO₂ spheres were used as templates to synthesize the uniform and mesoporous ZrO₂ HSs. As nanocontainers, ZrO₂ HSs could load hemin in its cavity via pores. Then, the aptamers of MUC1, as bio-gates, blocked the pores of ZrO₂ HSs based on the specific binding of Zr⁴⁺ and the phosphate groups of aptamer. In the presence of MUC1, the aptamer could specifically recognize and bind with MUC1, and then leave away from the surface of ZrO₂ HSs, which resulted in the opening of the bio-gates and releasing of hemin. Assisted with the G wires formed on the Au NPs/In₂S₃/ITO, the released hemin was captured on the electrode through the formation of hemin/G-quadruplex structure, leading to the switch of the photocurrent polarity of the electrode from anodic photocurrent to cathodic photocurrent. The proposed photoelectrochemical biosensor showed outstanding performance for MUC1 assay with high selectivity, wide linear response range (1 fg mL^-1 -10 ng mL^-1) and lower detection limit (0.48 fg mL^-1). And the strategy could be easily extended to a triple-mode detection of MUC1 because the hemin/G-quadruplex structure was widely used in electrochemical and colorimetric methods as a hydrogen peroxide mimetic enzyme, which might provide wide applications in biological or clinical studies.