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Lung cancer is a high-mortality cancer related to the concentration of neuron-specific enolase (NSE). In this work, a sandwich-type photoelectrochemical (PEC) immunosensor was constructed for ultrasensitive detection of NSE, which is based on iron trioxide/indium zinc cadmium sulfide (Fe 2 O 3 /Cd-ZnIn 2.2 S y ) as a sensing platform and Ag-modified polyaniline (Ag@PANI) as a signal amplification label. The 1D Fe 2 O 3 porous nanorods with a large specific surface area were synthesized by calcination of Fe-MIL-88A and etching of NaOH. To improve the photocurrent response, the 3D architecture Cd-ZnIn 2.2 S y was combined with the 1D Fe 2 O 3 porous nanorods to form a 1D Fe 2 O 3 /3D Cd-ZnIn 2.2 S y heterostructure. Specifically, the Fe 2 O 3 /Cd-ZnIn 2.2 S y heterostructure with a good energy level matching (the two can form a stepped energy level matching, which accelerates the transfer rate of electrons) can improve the separation efficiency of electron-hole pairs (e - /h + ) under visible light irradiation, which enhances the photocurrent response. Ag@PANI has a strong electron transport capability and can be used as a secondary antibody marker for the signal amplification of the immunosensor. The sensor exhibits a good linear detection range of 100 fg/mL to 100 ng/mL with a low detection limit of 33.5 fg/mL. Moreover, the constructed sandwich-type PEC immunosensor shows good performance and possesses excellent specificity, selectivity, and stability over a period of 4 weeks for NSE detection. With these excellent properties, the immunosensor can be extended to analyze and diagnose other disease biomarkers.

Based on the necessity and urgency of detecting infectious disease marker procalcitonin (PCT), a novel unlabeled photoelectrochemical (PEC) immunosensor was prepared for the rapid and sensitive detection of PCT. Firstly, SnO 2 porous nanoflowers with good photocatalytic performance were prepared by combining hydrothermal synthesis and calcining. BiOI nanoflowers were synthesized by facile ultrasonic mixed reaction. Ag 2 S quantum dots were deposited on SnO 2 /BiOI composites by in situ growth method. The SnO 2 /BiOI/Ag 2 S composites with excellent photoelectric properties were employed as substrate material, which could provide significantly enhanced and stable signal because of the energy level matching of SnO 2 , BiOI and Ag 2 S and the good light absorption performance. Accordingly, a PEC immunosensor based on SnO 2 /BiOI/Ag 2 S was constructed by using the layered modification method to achieve high sensitivity analysis of PCT. The linear dynamic range of the detection method was 0.50 pg·mL -1 ~100 ng·mL -1 , and the detection limit was 0.14 pg·mL -1 . In addition, the designed PEC immunosensor exhibited satisfactory sensitivity, selectivity, stability and repeatability, which opened up a new avenue for the analyzation of PCT and further provided guidance for antibiotic therapy.

Integrating a microfluidic sensor with a ratiometric photoelectrochemical (PEC) strategy to build a bioanalysis device for actual sample testing is often limited to large-volume space-resolution equipment and wavelength-dependent or potential-dependent paired photoactive materials. This work reports a microfluidic ratiometric magnetic-photoelectrochemical (M-PEC) biosensor on the photochromic composite platform to solve the above problems. In particular, as a proof-of-concept study, the platform Bi 2 WO 6- x /amorphous BiOCl nanosheets/Bi 2 S 3 (p-BWO-s) mediated by photochromic color centers and the magnetic photoactive secondary antibody marker ZnFe 2 O 4 @Ag 2 O are integrated on the microfluidic biosensor. By enhancement of the photochromic color centers, p-BWO-s outputs a considerable photocurrent signal. Meanwhile, the photoactivity of the secondary antibody marker can be changed with a magnetic field; thus, different photocurrent signals can be obtained to realize ratiometric detection. The quenching photocurrent signal without the magnetic field and the difference photocurrent signal under the magnetic field are quantitatively related to the target concentration, which unfolds a novel general strategy for bioanalysis. Different from traditional ratiometric PEC biosensors, this work characterizes the first ratiometric PEC biosensor based on an external magnetic field. Generally speaking, combined with different biorecognition cases, this scheme with good expansibility brings a unique new perspective.

A self-powered photoanode-supported photoelectrochemical (PEC) immunosensor was designed based on In 2 O 3 /In 2 S 3 /CdIn 2 S 4 as photoanode and PDA@CNTs as biocathode for the detection of CYFRA 21-1. In this proposal, In 2 O 3 /In 2 S 3 /CdIn 2 S 4 heterojunction modified indium-tin oxide (ITO) electrode was served as a substitute for platinum (Pt) counter electrode to provide an evident and stable photocurrent signal. The matched band structure of In 2 O 3 , In 2 S 3 and CdIn 2 S 4 as well as the unique hollow porous structure of In 2 O 3 /In 2 S 3 /CdIn 2 S 4 played a pivotal role in accelerating the separation and transfer of photocarrier. Meanwhile, PDA@CNTs with excellent conductivity further enhanced the photocurrent which was provided by photoanode In 2 O 3 /In 2 S 3 /CdIn 2 S 4 heterojunction. Besides, PDA could effectively capture the antibody (Ab) through Michael addition. Separating photoanode from the sensing biocathode was conducive to improve the anti-interference capability of PEC sensor because the reductive species in biologic media will change PEC properties of the photoanode interface. Under optimal conditions, the PEC immunosensor have realized the detection of CYFRA 21-1 (0.5 pg/mL - 50 ng/mL) and the detection limitation with 0.16 pg/mL. In addition, the proposed self-powered PEC sensor with acceptable selectivity, reproducibility, and stability provide a new horizon for designing PEC immunosensing platform in bioassays., (Copyright © 2020. Published by Elsevier B.V.)

In this work, a signal amplification competitive-type photoelectrochemical system comprised of bismuth sulfide/bismuth oxyiodide/zinc oxide (Bi 2 S 3 /BiOI/ZnO) nano-array as platform and Ag 2 S-modified aptamers probe DNA (p DNA@Ag 2 S) as competition content for rapid and sensitive detection of OTA in microfluidic devices. The BiOI nano-array was first growth on surfaces of ZnO by a simple electrodeposited method, which provided large specific surface area and high stability to solve distribution of sensing platform and loose of combination of sensing substrate. Then, the Bi 2 S 3 could be in-situ growth by self-sacrificial part Bi 3+ of BiOI to form heterojunction without destroying the structure of the nano-array. A strong photocurrent intensity was acquired by the Bi 2 S 3 /BiOI/ZnO modified onto indium tin oxide (ITO) electrode, due to its good matching cascade band-edge levels could improve efficient separation of photo-generated e - /h + pairs. After immobilizing with the capture DNA (c DNA) and the sequential hybridization of p DNA@Ag 2 S, the photocurrent intensity reduced obviously because part photo-generated electron transformed to Ag 2 S rather than Bi 2 S 3 /BiOI/ZnO electrode. Subsequently, the photocurrent intensity increased evident when immobilized the target OTA, owing to the OTA could bind the p DNA@Ag 2 S to form the specific-complex that were released from the electrode surface. Under optimal conditions, the prepared PEC microfluidic sensor exhibited a linear concentration of OTA from 0.01 pg/mL to 200 ng/mL with a low detection limit of 0.0035 pg/mL (S/N = 3). Furthermore, it achieved high sensitivity, good specificity, and acceptable stability and further provided an efficient method for sensitive detection of other target mycotoxins in practical application., (Copyright © 2020 Elsevier B.V. All rights reserved.)

In this work, a novel self-powered photoelectrochemical (PEC) aptasensor integrated photoanode and photocathode for the accurate and selective detection of 17β-estradiol (E 2 ) was proposed for the first time. FeOOH/In 2 S 3 heterojunction was built initially and used as a substitute for platinum (Pt) counter electrode. The matched band gap edge of FeOOH and In 2 S 3 facilitated the transfer of photo-generate electrons to photoanode, while the holes left in the valence band of photocathode (CuInS 2 ) can be attracted by the electrons flowed from the photoanode, which reduced the recombination of electron-hole pairs and promote the cathodic photocurrent. Under optimal conditions, the constructed cathodic aptasensor of E 2 presented linear scope in 10 fg/mL-1 μg/mL with detection limit of 3.65 fg/mL. Besides, the cathodic aptasensor exhibited admiring selectivity, stability and reproducibility. This work verified that the cathodic photocurrent response can be regulated by the corresponding photoanode which provided a new design thought for PEC aptasensor on the basis of p-type semiconductor., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A novel visible light photoelectrochemical immunosensor based on BiOBr/Bi 2 S 3 heterostructures was fabricated to detect squamous cell carcinoma antigen (SCCA). Bi 2 S 3 nanoparticles formed on the BiOBr microflowers by the self-sacrificial synthesis method based on the facile reaction between BiOBr and S 2- ions. The BiOBr/Bi 2 S 3 composites exhibited excellent visible light photoelectrochemical activity, when ascorbic acid (AA) was employed as a perfect electron donor. The photocurrent intensity of BiOBr/Bi 2 S 3 modified ITO electrode arrived at around 20 µA, which was approximately 30 times than that of pure BiOBr. Dopamine formed easily polydopamine film via self-polymerization on the surface of BiOBr/Bi 2 S 3 composites to immobilize SCCA antibody. Under the optimal condition, this photoelectrochemical immunosensor realized the ultrasensitive determination of SCCA. With the logarithm of SCCA concentration in the range of 0.001-75 ng mL -1 , the specific binding between SCCA and antibody led to the linearly decrease of photocurrent signal with a low detection limit of 0.3 pg mL -1 (S/N = 3). This facilely constructed photoelectrochemical immunosensor maybe have promising practical application in photocatalysis, analytical detection and biosensor, etc., (Copyright © 2019 Elsevier B.V. All rights reserved.)

A sandwich-type photoelectrochemical (PEC) immunosensing platform was designed for detection of amino-terminal pro-B-type natriuretic peptide (NT-pro BNP). Thereinto, flower-like Bi 2 WO 6 /Ag 2 S nanoparticles (F-Bi 2 WO 6 /Ag 2 S) were employed as photoelectrochemical matrix, and graphene oxide and polydopamine composite (GO/PDA) were prepared as signal labels. In this proposal, Ag 2 S was in-situ growth on the surface of F-Bi 2 WO 6 modified with thioglycolic acid (TGA). Specially, a cascade-like band-edge level between F-Bi 2 WO 6 and Ag 2 S effectively improved the photocurrent conversion efficiency and enhanced the photocurrent response. Then, the conjugated GO/PDA aimed to further amplify signal because PDA as electron donor could sweep the holes and inhibit the recombination of photogenerated electron-hole pairs, while GO owned brilliant conductivity speeding up the electrons transfer. The photocurrent increased with the amount of GO/PDA conjugates which had positive correlation with the NT-pro BNP. Under optimal experimental conditions, the proposed sandwich-type PEC immunosensor presented a desirable linear relationship ranged from 0.1 pg/mL to 100 ng/mL for NT-pro BNP with the detection limit of 0.03 pg/mL (S/N = 3). The prepared PEC immunosensor exhibited high stability and selectivity, which offered an innovative idea for the detection of other biomolecules., (Copyright © 2019 Elsevier B.V. All rights reserved.)

An ultrasensitive label-free photoelectrochemical (PEC) immunosensor with high visible-light activity was developed for quantitative detection of amyloid β-protein (Aβ) by cross-linking anti-Aβ antibody onto the Ag 2 S sensitized SnO 2 /SnS 2 nanocomposites. Specifically, SnO 2 with flower-like porous nanostructure was innovatively applied in PEC immunosensor as a basal material. It could form a heterostructure with SnS 2 , which brought about the sensitization of SnO 2 and enhanced the separation of photogenerated electrons and holes. Moreover, Ag 2 S was in-situ growth on the surface of SnO 2 /SnS 2 , which further enhanced the photocurrent response significantly. Therefore, SnO 2 /SnS 2 /Ag 2 S could form stepwise band-edge structure, which benefited the light harvesting and provided a good foundation for sensor construction and detection. Under optimal conditions, the PEC immunosensor was used to detect the content of Aβ and exhibited a wide linear concentration range from 0.5 pg mL -1 to 100 ng mL -1 , with low limit of detection (0.17 pg mL -1 ) and limit of quantification (0.56 pg mL -1 ). Additionally, the designed PEC immunosensor exhibited good reproducibility, specificity, and stability which may find potential applications in the biosensor, biomedicine, clinical diagnosis, photocatalysis and other related fields., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Rapidity and high sensitivity are the critical factors for the diagnoses of heart attacks and cardiac troponin I (cTnI) is used as a gold standard marker for its diagnosis. To realize the accurate detection of cTnI, a novel ultrasensitive photoelectrochemical (PEC) immunosensor for cTnI determination was developed upon dual inhibition effect of Ag@Cu 2 O core-shell submicron-particles(SPs) toward CdS sensitized the (001) facets of anatase titanium dioxide nanosheets (TiO 2 /CdS). In this study, the TiO 2 /CdS composite not only indicated stable and excellent photoelectric signal but also provided abundant functional group to immobilized cTnI antibodies (Ab 1 ). To obtain the high sensitivity, Ag@Cu 2 O core-shell SPs were used as labels of the secondary antibodies (Ab 2 ), owning to competitive absorption of light and consumption of electron donor, less light energy and electron donors arrived at the TiO 2 /CdS sensitization structure. Besides, the remarkable steric hindrance effect of Ag@Cu 2 O core-shell SPs labeled secondary antibodies (Ab 2 ) conjugates obstructed the transfer of electrons and diffusion of the electron donors to the photoelectrode surface, leading to further decrease of photocurrent. Therefore, the constructed immunosensor has an ultrasensitive response to cTnI in a liner range of 0.02 pg/mL to 50 ng/mL with a low detection limit of 6.7 fg/mL, and exhibits good sensitivity and admirable stability. Moreover, the strategy provided an efficient and novel approach for dual inhibition effect in PEC immunoassay development., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Signal amplification is crucial for obtaining low detection limits in electrochemical immunosensor. In this work, we developed a novel signal amplification strategy using Au@Ag nanoparticles loaded by polydopamine functionalized phenolic resin microporous carbon spheres (Au@Ag/PDA-PR-MCS). Phenolic resin microporous carbon spheres (PR-MCS) possesses uniform size and a large surface area (1656.8 m 2 g -1 ). Polydopamine (PDA) functionalized phenolic resin microporous carbon spheres (PDA-PR-MCS) retains the advantages of PR-MCS and possesses strong adsorption ability. With the unique structure of PDA-PR-MCS, it not only improves the loading capacity and dispersity of Au@Ag nanoparticles (Au@Ag NPs), but also enhances the stability for the combination of the Au@Ag NPs by chemical absorption between Au@Ag NPs and -NH 2 of PDA. The Au@Ag/PDA-PR-MCS exhibits extraordinary electrocatalytic activity towards reduction of hydrogen peroxide (H 2 O 2 ) to make the electrochemical response more sensitive. Furthermore, Au NPs with good biocompatibility and excellent conductivity were electrodeposited on the surface of electrode, which was used as a sensing platform to immobilize primary antibody (Ab 1 ) and accelerate the electron transfer on the electrode interface. Herein, the designed immunosensor provided a broad linear range from 20 fg/mL to 100 ng/mL for alpha fetoprotein (AFP) detection and a low detection limit of 6.7 fg/mL (signal-to-noise ratio of 3) under optimal experimental conditions. Moreover, the excellent performance in detection of human serum samples indicated that the proposed immunosensor will provide promising applications in clinical monitoring of AFP., (Copyright © 2018 Elsevier B.V. All rights reserved.)

A label-free photoelectrochemical (PEC) platform with high visible-light activity for quantitative detection of the ochratoxin A (OTA) was developed by assembly of Ag 2 S nanoparticles (NPs) sensitized on titanium dioxide/red blood cell-like shape bismuth vanadate (TiO 2 /S-BiVO 4 ) electrode via layer-by-layer (LBL) strategy. In this protocol, ascorbic acid was used as an efficient electron donor for scavenging photo-generated holes and inhibiting light driven electron-hole pair recombination. TiO 2 has good photoelectric activity and large surface area. The S-BiVO 4 with porous structure surfaces can contribute to the high photocurrent intensity under visible-light irradiation. Moreover, the Ag 2 S NPs were in-situ growth on surfaces of thioglycolic acid modified S-BiVO 4 , which enhanced photocurrent response and further improved the photocurrent conversion efficiency. Under optimal conditions, the PEC immunosensor exhibited a wide linear concentration range from 5pgmL -1 to 750ngmL -1 , with a low detection limit of 1.7pgmL -1 (S/N = 3) for OTA. Additionally, the designed immunosensor was performed with good stability, reproducibility and selectivity, thus opening up a new promising PEC platform for some other small molecules analysis., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Recently early diagnosis of squamous cell carcinoma antigen (SCCA) as a tumor maker of various cancers has increasingly attracted a lot of attention with heightening of incidence rate of cancer. The SCCA with low concentration in human serum should be diluted before detecting. Thus, an immunoassay with high sensitivity is significant for early detecting SCCA. Therefore, a nonenzymatic sandwich-type electrochemical immunosensor herein was conducted to quantitative detection of squamous cell carcinoma antigen (SCCA). The amino functionalized cobaltosic oxide @ ceric dioxide nanocubes with core-shell morphology were prepared to combine sea-urchin like gold @ platinum nanoparticles (Co 3 O 4 @CeO 2 -Au@Pt), and used as labels to conjugate with secondary antibodies for signal amplification. Due to the synergetic effect, excellent electrochemical property and superior auxiliary catalytic activity of Co 3 O 4 @CeO 2 -Au@Pt, high electrocatalytic current responses toward the reduction of hydrogen peroxide (H 2 O 2 ) were achieved. Besides, the electrodeposited gold nanoparticles (D-Au NPs) which were modified on glassy carbon electrodes (GCE) were used as antibodies carriers and sensing platforms. With the well cooperation of Co 3 O 4 @CeO 2 -Au@Pt and D-Au NPs, a broad linear range from 100fg/mL to 80ng/mL with a low detection limit of 33 fg/mL for detecting SCCA was achieved. In addition, the immunosensor displayed with good reproducibility, high selectivity and stability. The results are satisfactory when the proposed method has been applied to analyze human serum samples, indicating that the potential application is promising in clinical monitoring of tumor markers., (Copyright © 2017 Elsevier B.V. All rights reserved.)

In this work, a sensitive sandwich-type electrochemical immunosensor was designed for the quantitative detection of prostate-specific antigen (PSA) by amperometric i-t. The Au loaded on thionine functionalized graphene oxide (Au@Th/GO) was used as a platform to immobilize primary antibodies (Ab 1 ) and accelerate the electron transfer on the electrode interface. PtCu bimetallic hybrid were loaded on 2D/2D reduced graphene oxide/graphitic carbon nitride (PtCu@rGO/g-C 3 N 4 ) with large surface area and biocompatibility, which were employed as labels for combining secondary antibodies (Ab 2 ) and amplifying signals to improve the sensitivity of the designed immunosensor which attributes to its good activity for the reduction of hydrogen peroxide (H 2 O 2 ). Under optimal conditions, the designed immunosensor exhibited a linear concentration range from 50fg/mL to 40ng/mL, with a low detection limit of 16.6fg/mL (S/N=3) for PSA. Additionally, the designed immunosensor showed acceptable selectivity, reproducibility and stability. The satisfactory results in analyze human serum samples indicated potential application promising in clinical monitoring of tumor markers., (Copyright © 2017 Elsevier B.V. All rights reserved.)

In this work, a novel label-free electrochemical immunosensor was developed for the quantitative detection of prostate specific antigen (PSA). To this end, the amino functionalized cuprous oxide @ ceric dioxide (Cu 2 O@CeO 2 -NH 2 ) core-shell nanocomposites were prepared to bond gold nanoparticles (Au NPs) by constructing stable Au-N bond between Au NPs and -NH 2 . Because the synergetic effect presents in Cu 2 O@CeO 2 core-shell loaded with Au NPs (Cu 2 O@CeO 2 -Au), it shows better electrocatalytic activity towards the reduction of hydrogen peroxide (H 2 O 2 ) than single Cu 2 O, Au NPs and Cu 2 O@CeO 2 . Featured by large specific surface area, good biocompatibility and good electrochemical properties which can greatly improve the electronic transmission rate, Cu 2 O@CeO 2 -Au was used as transducing materials to achieve efficiently capture antibodies and triple signal amplification of the proposed immunosensor. Under the optimal conditions, the proposed immunosensor exhibited a wide linear range from 0.1pg/mL to 100ng/mL with a low detection limit of 0.03pg/mL (S/N=3). Furthermore, the proposed label-free immunosensor has been used to determine PSA in human serum with satisfactory results. Meanwhile, it displayed good reproducibility, acceptable selectivity, and long-term stability, which had promising application in bioassay analysis., (Copyright © 2016 Elsevier B.V. All rights reserved.)