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This work presents a photocurrent-polarity-switching-based photoelectrochemical (PEC) biosensing platform for ultrasensitive detection of microRNA-21 (miR-21) through target-triggered catalytic hairpin assembly (CHA) for modulation of methylene blue (MB) and ferrocene (Fc) positional configurations using double-shelled Cu-doped ZnS nanocages (NCs)-Au nanoparticles (NPs) as photoactive materials. In the presence of miR-21, the assembly of MB-labeled HP1 and Fc-labeled HP2 leads to the generation of a large amount of double-stranded DNA (HP1-HP2), which pushes MB away from the electrode surface and brings Fc close to the electrode surface, resulting in effectively quenching the enhanced PEC signal to activate the photocurrent-polarity-switching system. Benefiting from the distance-controllable strategy, the designed PEC bioanalysis can effectively eliminate false-positive and false-negative signals due to the change of different signal expression patterns (from traditional the "signal-on" mode to the photocurrent-polarity-switching mode), thereby significantly improving the sensing specificity and sensitivity. The proposed PEC sensing system exhibited satisfying photocurrent responses toward target miR-21 within the working range from 1.0 fM to 1 nM at a low limit of detection (LOD) of 0.58 fM. More importantly, we demonstrated the successful integration of the proposed PEC biosensor with a handheld wireless device for instant detection of miR-21 concentrations in practical samples.

(A) Schematic diagram of Co9S8 nanoparticle-decorated CdS nanoflowers-based photoelectrochemical (PEC) aptasensor for the detection of carcinoembryonic antigen (CEA); and (B) the photocurrent response mechanism of PEC bioanalysis.

This review summarizes recent advances on metal-organic frameworks for the applications in photoelectrochemical and electrochemiluminescence biosensors.

A new nucleic acid-based magnetic potentiometric aptasensing platform was designed for in situ amplified measurement of prostate-specific antigen with the catalytic hairpin assembly.

Large-scale, rapid, and inexpensive serological diagnoses of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) are of great interest in reducing virus transmission at the population level; however, their development is greatly plagued by the lack of available point-of-care methods, leading to low detection efficiency. Herein, an ultrasensitive smartphone-based electrochemical immunoassay is reported for rapid (less than 5 min), low-cost, easy-to-implement detection of the SARS-CoV-2 nucleocapsid protein (SARS-CoV-2 N protein). Specifically, the electrochemical immunoassay was fabricated on a screen-printed carbon electrode coated with electrodeposited gold nanoparticles, followed by incubation of anti-N antibody (Ab) and bovine serum albumin as the working electrode. Accompanied by the antigen-antibody reaction between the SARS-CoV-2 N protein and the Ab, the electron transfer between the electroactive species [Fe(CN)

Recently emerged Z-scheme heterostructure-based immunoassays have presented new opportunities for photoelectrochemical (PEC) biosensing development. Here, we described a tunable signal-on PEC biosensor for the detection of cardiac troponin I (cTnI), which exploited a competitive absorption effect between Cu(II) ions and a Zr metal-organic framework (Zr-MOF) constructed on TiO

Photoelectrochemical (PEC) biosensors incorporating biomolecular recognition with photon-to-electron conversion capabilities of the photoactive species have been developed for molecular diagnosis, but most involve difficulty in adjusting band gap positions and are unsuitable for PEC biodetection. In this work, an innovative PEC biosensor combined with quantum size-controlled engineering based on quantum confinement by controlling the quantum size was designed for the detection of human papillomavirus-16 (HPV-16) through CRISPR-Cas12a (Cpf1)-induced disassembly of Z-scheme heterojunction. To the best of our knowledge, quantum size-controlled engineering that precisely tunes the properties of photoactive materials is first utilized in the PEC bioanalysis. Based on the quantum size effect, the light absorption efficiency and charge-transfer rate were tuned to suitable levels to obtain the best PEC performance. After incubation with target HPV-16, the binding of Cas12a-crRNA to the target double-stranded DNA (dsDNA) stimulated the activity of indiscriminate cleavage toward single-stranded DNA (ssDNA), resulting in a decrease in photocurrent due to the blocking of electron transfer through the heterojunction. By optimizing experimental conditions, the Z-scheme sensing system exhibited incredible photocurrent response to HPV-16 in the range from 3.0 pM to 600 nM with a detection limit of 1.0 pM. Impressively, the application of the quantum size effect could stimulate more interest in the precise design of band gap structure to improve PEC performance.

The exact fabrication of precise three-dimensional structures for piezoresistive sensors necessitates superior manufacturing methods or tooling, which are accompanied by time-consuming processes and the potential for environmental harm. Herein, we demonstrated a method for

A ratiometric fluorescence enzyme-linked immunosorbent assay was constructed for the screening of alpha-fetoprotein using carbon dots@SiO2@CdTe quantum dots.

An autofluorescence-free immunosensing platform was designed to determine prostate-specific antigen based on the photoluminescence of CePO4:Tb nanocrystals.

Herein, we reported a novel photoelectrochemical immunoassay method based on a target-triggered on/off signal of the ultra-structured Bi2O2S (BOS) photoanode system for the sensitive testing of carcinoembryonic antigen (CEA) in serum samples.

Herein, we explore a general Cu2-x S nanocube template-assisted and reverse cation exchange-mediated growth strategy for fabricating hollow multinary metal sulfide. Unlike the traditional cation exchange method controlled by the metal sulfide constant, the introduction of tri-n-butylphosphine (TBP) can reverse cation exchange to give a series of hollow metal sulfides. A variety of hollow multinary metal sulfide cubic nanostructures has been demonstrated while preserving anisotropic shapes to the as-synthesized templates, including binary compounds (CdS, ZnS, Ag2 S, PbS, SnS), ternary compound (CuInS2 , Znx Cd1-x S), and quaternary compound (single-atom platinum anchored Znx Cd1-x S; Znx Cd1-x S-Pt1 ). Experimental and density functional theory (DFT) calculations show that the hollow metal sulfide semiconductors obtained could significantly improve the separation and migration of photogenerated electron-hole pairs. Owing to the efficient charge transfer, the Znx Cd1-x S-Pt1 exhibited outstanding photocatalytic performance of CO2 to CO, with the highest CO generation rate of 75.31 μmol h-1 .

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 Bi

Lab-based testing systems utilizing photoelectrochemical (PEC) biosensing methodologies for the ultrasensitive carcinoembryonic antigen (CEA) have been developed, although the majority have shown complicated operating procedures and dependence on precise apparatus. Herein, a portable photoelectrochemical split diagnostic platform based on a hollow CdS/CdMoO

Pressure-based immunoassays have been studied for point-of-care testing for which increasing the sensitivity is still a challenge. In this study, we described an enhanced pressure-based immunoassay with a versatile electronic sensor for the sensitive biological analysis. The versatile electronic sensor had multifunctional sensing capabilities with temperature and pressure recording. Magnetic bead-modified capture antibody and platinum nanoparticle-labeled detection antibody were used as the biorecognition element of the target carcinoembryonic antigen (CEA) (as a model analyte) and would form a sandwich-type immune complex with CEA. After simple magnetic separation, this complex was transferred into the detection chamber, which contained both hydrogen peroxide (H2O2) and 3,3',5,5'-tetramethylbenzidine (TMB). With the catalytic ability of PtNPs, the "H2O2-TMB-PtNPs" system was catalyzed to generate a large amount of oxygen (O2) and photothermal agent of oxidizer TMB (ox-TMB). Meanwhile, in a sealed chamber, further irradiation with an 808 nm near-infrared laser led to a triple-step signal amplification strategy of pressure increase, temperature increase, and gas thermal expansion to receive a strong electrical signal through the electronic sensor in real time. Thus, the amplified electrical signal from the electronic sensor could reveal the target concentration. In addition, we also verified that the synergistic system with two physical quantities had a lower limit of detection and a wider detection range compared to the detection system with a single physical quantity. In general, this immunoassay not only helped in exploring an effective signal amplification pathway but also offered an opportunity for the development of versatile electronic sensors in point-of-care settings.

The point-of-care (POC) method with affordability and portability for the sensitive detection of biological substances is an emerging topic in rapid disease screening and personalized medicine. In this work, we demonstrated a diverse responsive platform based on a dual-channel pressure sensor (DCPS). The DCPS had a multilayer flexible architecture consisting of a photonic hydrogel with chromatic transitions and a piezoresistive pressure sensor as the electrical data transmission unit, both of which had the property of pressure-induced mechanical stimulus feedback. By incorporating a platinum nanoparticles-labeled detection antibody (PtNPs-dAb) into the sandwich-type immunoreaction for the target carcinoembryonic antigen (CEA, as a model analyte), gas decomposition could be triggered by the addition of hydrogen peroxide (H

Herein, we developed a flexible, low-cost thermosensitive fiber paper for the visual display in photothermal biosensing systems for early acute myocardial infarction. The thermal signal visualization device was encapsulated with rewritable thermal fibers, which exhibited excellent stability and reversibility. The mechanism of color change in thermal paper was based on a temperature-driven reversible transformation of the structure of the dye molecule (crystalline violet lactone, CVL). It exhibits a gradation from blue to colorless at higher temperatures and gradually returns to blue when the temperature drops. Immobilization and cascade enzymatic reactions of target molecules occurred in an integrated 3D-printed detection device, a photothermal conversion process occurred under near-infrared light excitation, and the colorimetric change values of the encapsulated thermal paper were recorded and evaluated for possible pathogenicity using a smartphone. It was worth noting that the effect of the thermogenic ring-opening behavior of CVL on the macroscopic phenomenon of color change was obtained by density functional theory calculations. Under optimized conditions, the naked-eye-recognizable range of the thermal paper-based photothermal immunoassay sensor was 0.2-20 ng mL

Multi-signal output biosensor technologies based on optical visualization and electrochemical or other sophisticated signal transduction are flourishing. However, sensors with multiple signal outputs still exhibit some limitations, such as the additional requirement for multiple regression equation construction and control of results. Herein, we developed a sensitive cascade of colorimetric-photothermal biosensor models for prognostic management of patients with myocardial infarction with the assistance of an artificial neural network (ANN) normalization process. A cascade enzymatic reaction device based on hollow prussian blue nanoparticles (h-PB NPs), and a portable smartphone-adapted signal visualization platform were integrated into the all-in-one 3D printed assay device. Specifically, liposomes encapsulated with h-PB were confined to the test cell using a classical immunoassay. Based on the peroxidase-like activity of h-PB, the h-PB obtained by the immunization process was further transferred to the TMB-H

Exploiting innovative strategies with signal amplification in photoelectrochemical (PEC) biosensing systems to realize sensitive screening of low-abundance proteins has become one of the mainstream research orientations. Herein we reported a new strategy to amplify photocurrent signal employing a photocatalyst-electrolyte effect in alkaline media for the sensitive monitoring of prostate-specific antigen (PSA) using snowflake-liked CdS@ZnIn

Current methods for tuning the plasmonic properties of metallic nanoparticles typically rely on alternating the morphology (i.e., size and/or shape) of nanoparticles. The variation of morphology of plasmonic nanoparticles oftentimes impairs their performance in certain applications. In this study, we report an effective approach based on the control of internal structure to engineer morphology-invariant nanoparticles with tunable plasmonic properties. Specifically, these nanoparticles were prepared through selective growth of Ag on the inner surfaces of preformed Ag-Au alloyed nanocages as the seeds to form Ag@(Ag-Au) shell@shell nanocages. Plasmonic properties of the Ag@(Ag-Au) nanocages can be conveniently and effectively tuned by varying the amount of Ag deposited on the inner surfaces, during which the overall morphology of the nanocages remains unchanged. To demonstrate the potential applications of the Ag@(Ag-Au) nanocages, they were applied to colorimetric sensing of human carcinoembryonic antigen (CEA) that achieved low detection limits. This work provides a meaningful concept to design and craft plasmonic nanoparticles.

This work demonstrated a pressure-based biosensor integrated with a flexible pressure sensor and an electrochromic device for visual detection. Initially, a sandwich-type immunoreaction for target carcinoembryonic antigen (CEA, as a model analyte) was carried out using the capture antibody (cAb) and platinum nanoparticles-labeled detection antibody (PtNPs-dAb) in a reaction cell. The added hydrogen peroxide (H2O2) could be catalyzed by the PtNPs to generate oxygen (O2). In a sealed chamber, the pressure increased with the overflowing O2. Meanwhile, a skin-inspired flexible pressure sensor with excellent sensing performance was fabricated to monitor the pressure change in real time. Thus, the electrical signal of the pressure sensor could reveal the target concentration. Moreover, a voltage-regulated electrochromic device based on polyaniline (PANI) and tungsten oxide (WO3) was integrated into the platform to provide a visualized readout. According to the electrical signal of the pressure sensor, the electrochromic device would change its color from green to blue, which also revealed the target concentration and could be observed by the naked eye. Under optimal conditions, the biosensor presented a high sensitivity for CEA in a detectable range of 0.2-50 ng/mL. The limit of detection (LOD) was 94 pg/mL. The selectivity, reproducibility, and accuracy were also satisfying. Furthermore, this immunoassay gives a path for developing visualized biosensors in point-of-care settings.

Efficient separation of photo-induced electrons and holes in the photoelectrochemical (PEC) sensors plays an important role in improving detection sensitivity. Based on this point, we report a simple and sensitive photoelectrochemical bioassay for prostate-specific antigen (PSA) detection using lanthanide-doped bismuth ferrite/reduced graphene oxide/tungsten oxide nanohybrids (BLFO/rGO/WO3) as the photo-sensing material. Initially, WO3 was excited under the continuous illumination to generate photo-induced electron–hole pairs. Then, rGO (as a suitable charge transfer medium) could effectively build a bridge between WO3 and BLFO. With the mediation of the built-in electric field in BLFO, the transferred charges were allowed for directional migration in the circuit, thus achieving an effective separation of the photogenerated electron–hole pairs. Coupling with the amplification of enzymatic production (H2O2) and specific recognition of antigen–antibody immunoreaction, target concentration was relative to the corresponding photocurrent, thereby realizing the PSA sensitive detection. Under optimal conditions, the PEC immunoassay exhibited a good linear relationship within a dynamic working range from 0.1 ng mL−1 to 200 ng mL−1 with a detection limit of 49.4 pg mL−1. In addition, this study afforded satisfying specificity, reproducibility, and long-term storage, which also matched well with the commercial PSA ELISA kit.

Herein a rapid and sensitive fluorometric bioanalysis platform for mercury(ii) (Hg2+) detection was innovatively developed using ultrathin two-dimensional MXenes (Ti3C2) as fluorescence quencher and Hg2+-induced exonuclease III (Exo III)-assisted target recycling strategy for efficient signal amplification. Initially, fluorophore-labeled single-stranded DNA (FAM-labeled probe) can be easily adsorbed onto the surface of ultrathin Ti3C2 nanosheets by hydrogen bonding and metal chelating interaction, and the fluorescence signal emitted by the FAM-labeled probe is quenched strongly owing to the fluorescence resonance energy transfer between the FAM and ultrathin Ti3C2 nanosheets. Upon sensing the target Hg2+, the protruding DNA fragment at the 3' end of hairpin will hybridize with primer (hairpin-Hg2+-primer), and then further digested by Exo III to produce a probe (nicker). The released target Hg2+ and primer continue to participate in the next recycling, resulting in more hairpin probes becoming nickers. The combination of a large number of nickers and FAM-probe resulted in a significant increase in the fluorescence signal of the system, which was attributed to the fact that the double helix DNA was more rigid and separated from the surface of the ultrathin Ti3C2 nanosheets. The obvious fluorescence signal change of the Ti3C2-based Exo III-assisted target recycling can be accurately monitored by fluorescence spectrometry, which is also proportional to the concentration of Hg2+. Under optimum operating conditions, the peak intensity (520 nm wavelength) of fluorescence increased with increasing Hg2+ within a wide dynamic working range from 0.05 nM to 50 nM (R2 = 0.9913) with a limit of detection down to 42.5 pM. The proposed strategy uses ultrathin MXenes as a platform for binding nucleic acids, which contributes to its potential in nucleic acid hybridization-based biosensing and/or nucleic acid signal amplification bio-applications.

Biotoxins present in foods represent a major source of contamination. Although different analytical methods have been developed, a new detection method for identification and quantification of these toxins is necessary for extending their application sphere. Therefore, in this study, an enzyme-controlled citrate-iron(III) chelating system was used to build a novel colorimetric immunoassay sensing platform for detection of ochratoxin A (OTA). The experimental signal was derived from the reaction of iron(III) and 3,3′,5,5′-tetramethylbenzidine (TMB). However, the addition of citrate could combine with iron(III) rapidly, thereby hindering the reaction of iron(III) and TMB for production of the signal (i.e., colorless to blue). Additionally, hydrogen peroxide (H2O2), which could be produced from glucose in the presence of glucose oxidase (GOx), could affect the binding capacity of citrate and iron(III), thereby releasing iron(III) to react with TMB. That is to say, different amounts of GOx could regulate the intensity of the signal. Based on these findings, magnetic bead (MB)-based OTA competed with dissociative OTA (added) for glucose oxidase (GOx)-labelled anti-OTA. As the dissociative OTA concentration increased, the amount of GOx-labelled anti-OTA on MB conveniently reduced and the absorbance decreased. The method exhibited a good linear relationship as the concentration of the target (OTA) increased from 0.005 to 5 ng mL−1; the detection limit was 4.2 pg mL−1, as estimated based on the 3Sblank level under optimal conditions. The specificity and feasibility for a real sample of the colorimetric immunoassay was acceptable, respectively. The current results provided important insights into the development of citrate-iron(III) chelating system-based biological detection methods and colorimetric immunoassays.