Photocurrent Polarity Switching Research Articles

CRISPR-Enhanced Photocurrent Polarity Switching for Dual-lncRNA Detection Combining Deep Learning for Cancer Diagnosis.

Abnormal expression in long noncoding RNAs (lncRNAs) is closely associated with cancers. Herein, a novel CRISPR/Cas13a-enhanced photocurrent-polarity-switching photoelectrochemical (PEC) biosensor was engineered for the joint detection of dual lncRNAs, using deep learning (DL) to assist in cancer diagnosis. After target lncRNA-activated CRISPR/Cas13a cleaves to induce DNAzyme bidirectional walkers with the help of cofactor Mg2+, nitrogen-doped carbon-Cu/Cu2O octahedra are introduced into the biosensor, producing a photocurrent in the opposite direction of CdS quantum dots (QDs). The developed PEC biosensor shows high specificity and sensitivity with limits of detection down to 25.5 aM for lncRNA HOTAIR and 53.1 aM for lncRNA MALAT1. More importantly, this platform for the lncRNA joint assay in whole blood can successfully differentiate cancers from healthy people. Furthermore, the DL model is applied to explore the potential pattern hidden in data of the established technology, and the accuracy of DL cancer diagnosis can acquire 93.3%. Consequently, the developed platform offers a new avenue for lncRNA joint detection and early intelligent diagnosis of cancer.

Photocurrent polarity switching photoelectrochemical aptasensor for oxytetracycline based on BiOBr/Ag2S/PDA//CuO: CuO-induced II-type to dual Z-scheme system

BackgroundAs a broad-spectrum tetracycline antibiotic, Oxytetracycline (OTC) was widely used in a variety of applications. But, the overuse of OTC had led to the detection of it in food, water and soil, which could present significance risk to human health and cause damage to ecosystem. It was of great significance to develop sensitive detection methods for OTC.Herein, an environmentally friendly photoelectrochemical (PEC) aptasensor was constructed for the sensitive detection of OTC based on CuO-induced BiOBr/Ag2S/PDA (Polydopamine) photocurrent polarity reversal. ResultsBiOBr/Ag2S/PDA composites modified electrode not only produced stable initial anodic photocurrent but also provided attachment sites for the aptamer S1 of OTC by the strong adhesion of PDA. On the other hand, CuO loaded OTC aptamer S2 (Cu–S2) was got through Cu–S bonds. After the target OTC was identified on the electrode surface, CuO was introduced to the surface of ITO/BiOBr/Ag2S/PDA through the specific binding of OTC to S2. This identification process formed dual Z-type heterojunctions and resulted in a remarkable reversal of photocurrent polarity from anodic to cathodic. Under optimization conditions, the PEC aptasensor showed a wide linear range (50 fM ∼ 100 nM), low detection limit (1.9 fM), excellent selectivity, stability and reproducibility for the detection of OTC. Moreover, it was successfully used for the analysis of OTC in real samples of tap water, milk and honey, and had the potential for practical application. SignificanceThis work developed an environmentally friendly photocurrent-polarity-switching PEC aptasensor with excellent selectivity, reproducibility, stability, low LOD and wide linear range for OTC detection. This sensitive system, which was including BiOBr, Ag2S, PDA and CuO were low toxicity, not only reduced the risk of traditional toxic semiconductors to operators and the environment, but can also be used for the detection of real samples, broadening the wider range of applications for BiOBr, Ag2S, PDA and CuO.

A novel split PEC sensor based on magneto–optic nanostructure and photocurrent polarity switching strategy

BackgroundPhotoelectrochemical (PEC) sensors have attracted much attention due to their low cost, simple instrumentation and high sensitivity. However, conventional PEC sensors require layer–by–layer modification of the photoelectrode surface, which has the disadvantages of being time–consuming and unstable. In addition, complex interfering substances in real samples may lead to false–positive or false–negative detection results. It was thought that the above drawbacks could be eliminated by the construction of a polarity inversion PEC sensor. In this work, a magnetically separated PEC sensor was constructed for the detection of Carcinoembryonic antigen (CEA). ResultsDuring the experiment, the construction of the sensor was used for sensitive detection of CEA. In the experimental process, Fe3O4@SiO2@CdS, a semiconductor material with magnetic properties, was chosen as the substrate material, and ZnO/CuO was used as the marker on the DNA2 molecule, and a split magnetic separation PEC sensor was constructed, which was used to realize the sensitive detection of CEA. Eventually, the detection range of the sensor for CEA detection is 1–10000 pg/mL, with the detection limit of 0.34 pg/mL. Additionally, the PEC sensor has the advantages of high speed, high efficiency, high sensitivity, good specificity, and high stability. The sensing platform constructed in this work can also be extended to detect other targets, which provides a new idea for PEC sensing platforms. SignificanceIn this experiment, we developed a split PEC immunosensor based on magneto–optic nanostructure and photocurrent polarity switching strategy. Specifically, the proposed magnetic nanostructure Fe3O4@SiO2@CdS–DNA1 exhibits good paramagnetism and dispersion ability. By magnetic separation process, the PEC signals of opposite polarity can be obtained.

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.

G-Quadruplex/Hemin-Mediated Polarity-Switchable and Photocurrent-Amplified System for Escherichia coli O157:H7 Detection.

The contamination of food by pathogens is a serious problem in global food safety, and current methods of detection are costly, time-consuming, and cumbersome. Therefore, it is necessary to develop rapid, portable, and sensitive assays for foodborne pathogens. In addition, assays for foodborne pathogens must be resistant to interference resulting from the complex food matrix to prevent false positives and negatives. In this study, hemin and reduced graphene oxide-MoS2 sheets (GMS) were used to design a near-infrared (NIR)-responsive photoelectrochemical (PEC) aptasensor with target-induced photocurrent polarity switching based on a hairpin aptamer (Hp) with a G-quadruplex motif. A ready-to-use analytical device was developed by immobilizing GMS on the surface of a commercial screen-printed electrode, followed by the attachment of the aptamer. In the presence of Escherichia coli O157:H7, the binding sites of Hp with the G-quadruplex motif were opened and exposed to hemin, leading to the formation of a G-quadruplex/hemin DNAzyme. Crucially, after binding to hemin, the charge transfer pathway of GMS changes, resulting in a switch of the photocurrent polarity. Further, G-quadruplex/hemin DNAzyme enhanced the cathodic photocurrent, and the proposed sensor exhibited a wide linear range ((25.0-1.0) × 107 CFU/mL), a low limit of detection (2.0 CFU/mL), and good anti-interference performance. These findings expand the applications of NIR-responsive PEC materials and provide versatile PEC methods for detecting biological analytes, especially for food safety testing.

Target-Induced Photocurrent-Polarity-Switching PEC Sensing Platform Based on In Situ Generation of Oxygen Vacancy-Modulated Energy Band Structures.

The polarity of the photocurrent can be modulated by tunable bipolar photoelectrochemical (PEC) behavior, which is anticipated to address the issues of high background signal caused by traditional unidirectional increasing/decreasing response and false-positive/false-negative problems. Here, a new approach is suggested for the first time, which employs a target-induced enzyme-catalyzed reaction and in situ oxygen vacancy (OV) generation to achieve heterojunction photocurrent switching for highly sensitive detection of alkaline phosphatase (ALP). Among them, the ALP can catalyze the decomposition of ascorbic acid phosphate to produce ascorbic acid, which not only acts as an electron donor to change the redox environment but also acts as a reducing agent to introduce OVs into BiOBr semiconductors in cooperation with illumination. The introduction of vacancies can effectively modulate the energy band structure of BiOBr, while with the change of redox conditions, the transfer path of photogenerated carriers is changed, thus realizing the switching of photocurrents, which leads to its use in the construction of a negative-background anti-interference PEC sensing platform, achieving a wide linear range from 0.005 to 500 U·L-1 with a low detection limit of 0.0017 U·L-1. In conclusion, the photocurrent switching operation of this system is jointly regulated by chemistry, optics, and carrier motion, which provides a new idea for the construction of a PEC sensing platform based on photocurrent polarity switching.

Photocurrent Generation and Polarity Switching in Electrochemical Cells through Light‐induced Excited State Proton Transfer of Photoacids and Photobases**

AbstractLight is a common source of energy in sustainable technologies for photocurrent generation. To date, in such light‐harvesting applications, the excited electrons generate the photocurrent. Here, we introduce a new mechanism for photocurrent generation that is based on excited state proton transfer (ESPT) of photoacids and photobases that can donate or accept a proton, respectively, but only after excitation. We show that the formed ions following ESPT can either serve as electron donors or acceptors with the electrodes, or modify the kinetics of mass transport across the diffuse layer, both resulting in photocurrent generation. We further show that control of the current polarity is obtained by switching the irradiation between the photoacid and the photobase. Our study represents a new approach in photoelectrochemistry by introducing ESPT processes, which can be further utilized in light‐responsive energy production or energy storage.

Photocurrent Generation and Polarity Switching in Electrochemical Cells through Light-induced Excited State Proton Transfer of Photoacids and Photobases.

Light is a common source of energy in sustainable technologies for photocurrent generation. To date, in such light-harvesting applications, the excited electrons generate the photocurrent. Here, we introduce a new mechanism for photocurrent generation that is based on excited state proton transfer (ESPT) of photoacids and photobases that can donate or accept a proton, respectively, but only after excitation. We show that the formed ions following ESPT can either serve as electron donors or acceptors with the electrodes, or modify the kinetics of mass transport across the diffuse layer, both resulting in photocurrent generation. We further show that control of the current polarity is obtained by switching the irradiation between the photoacid and the photobase. Our study represents a new approach in photoelectrochemistry by introducing ESPT processes, which can be further utilized in light-responsive energy production or energy storage.

Photoelectrochemical polarity-switching-mode and split-type biosensor based on SQ-COFs/BiOBr heterostructure for the detection of uracil-DNA glycosylase

Here, we constructed a split-type and photocurrent polarity switching photoelectrochemical (PEC) biosensor for ultrasensitive detection of Uracil-DNA glycosylase (UDG, abnormal UDG activity is correlated with human immunodeficiency, cancers, bloom syndrome, neurodegenerative diseases and so on) based on SQ-COFs/BiOBr heterostructure, as the photoactive materials, methylene blue (MB) as the signal sensitizer, and catalytic hairpin assembly (CHA) for signal amplification. Specifically, the photocurrent intensity generated by SQ-COFs/BiOBr was about 2 and 6.4 times of that of BiOBr and SQ-COFs alone, which could be responsible for the detection sensitivity for the proposed biosensor. In addition, it is not common to construct heterojunctions between covalent organic skeletons and inorganic nanomaterials. In UDG recognition tube, the plenty of COP probes loaded methylene blue (MB) were obtained by magnetic separation with the help of the simple chain displacement reaction of CHA. MB, as a responsive substance, can efficiently switched the photocurrent polarity of the SQ-COFs/BiOBr electrode from cathode to anode, which reduce the background signal, further improve the sensitivity of the biosensor. Based on the above, the linear detection range of our designed biosensor is 0.001–3 U mL−1, and the detection limit (LODs) is as low as 4.07 × 10−6 U mL−1. Furthermore, the biosensor can still maintain good analytical performance for UDG in real sample, which means that it has broad application prospects in the field of biomedicine.

Hairpin DNAs conformational changes inducing opposite-polarity photoelectric signals recovery for simultaneous monitoring of dual microRNAs

Building flexible and reliable photoelectrochemical (PEC) sensors capable of measuring multiple miRNAs simultaneously still suffers from a challenge. In this protocol, a unique multiplexed PEC biosensor for miRNA-141 and miRNA-155 was developed by Fe3O4 @SiO2 @CdS-HP1-Ag2S NPs and CdTe QDs-HP2-Au NPs nanobioprobes polarity switching mode. HP1 and HP2 can be simultaneously unfolded by the two targets. The corresponding rigid DNA double-strand structure makes the distance between CdS shells and Ag2S NPs even greater, exposing more photoactive sites of CdS shells and thus the enhanced photoanode current. Similarly, the exciton-plasmon interaction (EPI) between the CdTe QDs and the Au NPs is disrupted, resulting in the photocurrent recovery of the CdTe QDs. Through external magnetic force, the one-step electrode modification of each above nanobioprobe was realized and the photocurrent polarity switching was also achieved. The linearity range of the designed multiplexed PEC biosensor was from 50 fM to 10 nM, and the detection limits reached 40.8 fM and 37.5 fM, respectively, without using any bioamplification technology. In addition, the manufactured PEC biosensor has significant advantages in compactness, short signal acquisition time, cost-effectiveness, as well as stability and replicability. The unique design provides a new perspective for monitoring multiple miRNAs simultaneously.

Photocurrent Polarity Switching and Enhanced Photoresponse in Silver Nanoparticles Decorated a-GaN-Based Photodetector

The photodetection properties of a-GaN nanorods-based photodetector and the effect of decorating silver nanoparticles are reported. For the pristine a-GaN detector, a surprising phenomenon of negative photoconductivity is observed, explained on the basis of defect states present in GaN nanorods. After the introduction of nanoparticles, the device exhibits reversal in the photocurrent polarity. The photoresponsivity reverses its sign from −0.12 A/W (bare a-GaN) to +6.75 A/W, with the introduction of nanoparticles (wavelength: 355 nm, 4.9 V bias). This current reversal and enhanced performance have been rationalized by considering passivation of surface defect states, resulting into significantly reduced dark current in the hybrid detector.

Nickel Single-Atom Catalyst-Mediated Efficient Redox Cycle Enables Self-Checking Photoelectrochemical Biosensing with Dual Photocurrent Readouts.

Developing a self-checking photoelectrochemical biosensor with dual photocurrent signals could efficiently eliminate false-positive or false-negative signals. Herein, a novel biosensor with dual photocurrent responses was established for the detection of acetylcholinesterase activity. To achieve photocurrent polarity-switchable behavior, the iodide/tri-iodide redox couple was innovatively introduced to simultaneously consume the photoexcited electrons and holes, which circumvents the inconvenience caused by the addition of different hole- and electron-trapping agents in the electrolyte. Importantly, benefiting from the high catalytic activity, the enhanced photoelectric responsivity can be realized after decorating the counter electrode with nickel single-atom catalysts, which promotes a more efficient iodide/tri-iodide redox reaction under low applied voltages. It is envisioned that the proposed photocurrent polarity switching system offers new routes to sensitive and reliable biosensing.

Bifunctional Magnetic Fe3O4@Cu2O@TiO2 Nanosphere-Mediated Dual-Mode Assay of PTP1B Activity Based on Photocurrent Polarity Switching and Nanozyme-Engineered Biocatalytic Precipitation Strategies.

Dysregulation of protein phosphatases is associated with the progression of various human diseases and cancers. Herein, a photoelectrochemical (PEC)-quartz crystal microbalance (QCM) dual-mode sensing platform was developed for protein tyrosine phosphatase 1B (PTP1B) activity assay based on bifunctional magnetic Fe3O4@Cu2O@TiO2 nanosphere-mediated PEC photocurrent polarity switching and QCM signal amplification strategies. The PTP1B-specific phosphopeptide (P-peptide) with a cysteine end was designed and immobilized onto the QCM Au chip via the Au-S bond. Subsequently, the Fe3O4@Cu2O@TiO2 nanosphere was connected to the P-peptide via the specific interaction between the phosphate group on the P-peptide and TiO2. After incubation with PTP1B, the dephosphorylation of the P-peptide occurred, causing some Fe3O4@Cu2O@TiO2 nanospheres to be released from the chip surface. The released magnetic Fe3O4@Cu2O@TiO2 nanospheres (labeled as R-Fe3O4@Cu2O@TiO2) were quickly separated via magnetic separation technology and attached to the Bi2S3-decorated magnetic indium-tin oxide (Bi2S3/MITO) electrode by magnetic force, inducing the switch of the photocurrent polarity of the electrode from anodic current (the Bi2S3/MITO electrode) to cathodic current (the R-Fe3O4@Cu2O@TiO2/Bi2S3/MITO electrode). Also, the nondephosphorylated P-peptide linked Fe3O4@Cu2O@TiO2 nanospheres as nanozymes with horseradish peroxidase activity to catalyze the formation of precipitation on the surface of the Au chip, leading to a frequency change of the QCM. Thus, the proposed PEC-QCM dual-mode sensing platform achieved accurate and reliable assay of PTP1B activity because of the different mechanisms and independent signal transductions. In addition, this dual-mode sensing platform can be easily extended for other protein phosphatase activity analysis and shows great potential in the early diagnosis of the protein phosphatase-related diseases and the protein phosphatase-targeted drug discovery.

Multicomponent Cu@Cu2O@C hybrid-induced photocurrent polarity switching biosensing strategy for the detection of TK1 mRNA

Thymidine kinase 1 messenger RNA (TK1 mRNA) is an attractive biomarker that plays an important role in the cancer diagnosis and prognostic treatment. Herein, an ultrasensitive and selectivity photoelectrochemical (PEC) biosensor is proposed for TK1 mRNA detection based on the multicomponent Cu@Cu2O@C hybrid-induced photocurrent polarity switching of titanium dioxide nanoparticles (TiO2 NPs). The multicomponent Cu@Cu2O@C hybrid with porous structure and specific surface area is successfully synthesized through the carbonization of copper metal organic frameworks (Cu-MOFs) in a nitrogen atmosphere, followed by the spontaneous oxidation of Cu. Through the TK1 mRNA-mediated chain displacement reaction, the Cu@Cu2O@C hybrid is introduced into the TiO2 NPs-modified electrode surface, resulting in the photocurrent polarity switching from anodic to cathodic photocurrents. Originating from high porosity, specific surface area, multicomponent synergistic effect, and efficient photocurrent-polarity-switching capability of the Cu@Cu2O@C hybrid, the constructed PEC biosensor for TK1 mRNA detection shows a wide linear range (1–5000 fM) with a lower detection limit (0.59 fM), and excellent anti-interference ability. Furthermore, the designed multicomponent Cu@Cu2O@C hybrid serves as an excellent photocurrent polarity switcher for constructing a PEC biosensor, and may have great potential in biological analysis and clinical diagnosis.

Target-induced photocurrent-polarity-switching photoelectrochemical aptasensor with gold nanoparticle-ZnIn2S4 nanohybrids for the quantification of 8-hydroxy-2′-deoxyguanosine

This work reports on an ultrasensitive photoelectrochemical (PEC) aptasensor for the detection of 8-hydroxy-2′-deoxyguanosine (8-OHdG) by using target-triggered hemin/G-quadruplex photocurrent polarity switching on ultrathin ZnIn2S4 nanosheets (ZISNS). Hemin/G-quadruplexes were assembled on indium tin oxide (ITO) electrodes coated with gold nanoparticle-modified ZISNS (AuNPs-ZISNS) as signaling labels for the polarity inversion mechanism in PEC aptasensors. Benefiting from the excellent photoelectronic properties of AuNPs-ZISNS and the photocurrent polarity switching reliability of hemin, the proposed aptasensor for 8-OHdG detection was in a broad range from 1.0 pM to 10,000 pM with a detection limit of 0.3 pM. Moreover, this assay has shown sufficient sensitivity, favorable stability, and high selectivity in the detection of complex biological matrices. The recoveries were in the range of 92–108%, and the relative standard derivations (RSD) were ranged from 2.1% to 5.1%, indicating the good accuracy and high precision of this approach. Impressively, the concept of photocurrent-polarity-switching mode provides an alternative for constructing accurate and plausible PEC bioanalysis and inspires more interest in the design of advanced PEC bioanalysis through readout signal regulation.

Two-dimensional Ti2C MXene-induced photocurrent polarity switching photoelectrochemical biosensing platform for ultrasensitive and selective detection of soluble CD146

Two-dimensional (2D) materials with unique structures and fascinating photoelectric properties are typically employed as supporting materials but they have not been mentioned in the context of polarity-reversal-mode photoelectrochemical (PEC) biosensors. Herein, a novel 2D Ti2C MXene-induced photocurrent polarity switching PEC biosensing platform was constructed for the selective and ultrasensitive detection of soluble CD146 (sCD146). Ag2S quantum dots (QDs)-fixed indium-tin oxide slices were used as the photocathode electrodes, and the capture antibody (Ab1) was assembled on the electrode. When the target sCD146 existed, 2D Ti2C MXene labeled with the detection antibody (Ab2) was introduced onto the modified electrode through a typical antigen-antibody sandwich immune reaction, resulting in a polarity switch from a cathodic to an anodic photocurrent. The outstanding optical and electron-transfer capability of the 2D Ti2C MXene made it beneficial to establish a high-performance photocurrent polarity switching PEC biosensor for sCD146 assay, and a linear response range of 0.1–1000 pg/mL with a detection limit of 18 fg/mL was obtained. Furthermore, the developed PEC biosensing strategy possessed excellent anti-interference ability for precluding the false positive or negative signals. The designed 2D Ti2C MXene opens up a new two-dimensional photocurrent-polarity switcher for constructing high-performance PEC biosensors, and the environmentally friendly 2D Ti2C MXene//Ag2S QDs photocurrent polarity switching system could overcome the harmfulness of conventional toxic semiconductors for operators and the environment, offering great potential applications in biological analysis and disease diagnosis.

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.

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.

Magnetic-Assisted Methylene Blue-Intercalated Amplified dsDNA for Polarity-Switching-Mode Photoelectrochemical Aptasensing.

Organic dyes are typically applied as photosensitizers in photoelectrochemical (PEC) cells but have not been reported in polarity-reversal-mode PEC sensors with excellent sensitivity and accuracy. Herein, an elegant and robust PEC biosensor for carcinoembryonic antigen (CEA) has been designed by photocurrent polarity switching of CdTe quantum dots (QDs), which is obtained by embedding methylene blue (MB) into amplified double-stranded DNA (dsDNA) anchored to the superparamagnetic Fe3O4@SiO2. The target-triggered Exo III-assisted cyclic amplification strategy and in situ magnetic enrichment enable the remarkable sensitivity. The extraction of target-analogue single-stranded DNA (output DNA) contributes to high selectivity resulting from the elimination of possible interferences in real samples or matrixes. Particularly, this exclusive polarity-reversal-mode PEC aptasensing can efficiently eliminate the false-positive or false-negative signals, leading to accurate measurements. Moreover, different from the probes and layer-by-layer assembled photoelectric beacons on electrodes in advance, this rational split-type approach is doomed to help the PEC biosensor with additional merits of convenient fabrication, short time consumption, wider linearity, as well as outstanding reproducibility and stability in practical applications. In light of the ability of MB acting as a kind of signal probe in typical electrochemical sensors, certainly, this ingenious design can not only be extended to a wide variety of target monitoring but also provide new ideas for the construction of high-performance electrochemical and PEC biosensors.

Peptide Cleavage-Mediated and Environmentally Friendly Photocurrent Polarity Switching System for Prostate-Specific Antigen Assay.

As the most important serum biomarker for prostate cancer, sensitive and accurate detection of prostate-specific antigen (PSA) is of great reference value for the clinical diagnosis and treatment of prostate cancer. Herein, a peptide cleavage-mediated and environmentally friendly photocurrent polarity switching system was developed for ultrasensitive and highly selective detection of PSA based on the efficiently switching of photocurrent polarity of silver indium sulfide nanoparticles (AgInS2 NPs)-coated indium tin oxide (ITO) electrode by amino-functionalized CuO cubes (NH2-CuO). The porous CuO cubes were synthesized by calcination of HKUST-1 and functionalized with aminosilane. In the presence of PSA, the biotin and rhodamine B-labeled peptide (Bio-Pep-RhB) was cleaved and part of the peptide (P-Pep-RhB) was obtained by magnetic separation. Through host-guest recognition between β-CD and RhB, the P-Pep-RhB was immobilized on the β-CD/AgInS2 NPs/ITO electrode. Then, the amino-rich sequence on P-Pep-RhB combined with NH2-CuO via glutaraldehyde results in the switch of anodic photocurrent to cathodic photocurrent. On account of the high-efficient peptide cleaving strategy and the new photocurrent polarity switching system of porous CuO cubes//AgInS2 NPs, the prepared sensing platform displayed outstanding analytical performance for PSA with a wide linear response range (0.1 pg mL-1-100 ng mL-1) and a lower detection limit of 0.06 pg mL-1. The proposed analytical method could be easily extended to analyze other proteins via changing the peptide sequence, which has a potential application in the fields of biological analysis and medical diagnosis.