Chiral covalent organic framework incorporated organic polymer monolithic capillary column for enantioseparations.

A chiral covalent organic framework was synthesized, characterized, and incorporated into organic polymer monolithic capillary columns to provide chiral stationary phases for enantioseparations. The prepared monolithic capillary columns were characterized by scanning electron microscopy and elemental analysis. To obtain better enantioseparations, the columns' preparation conditions, and enantioseparation conditions were optimized. Baseline resolutions of several chiral compounds were obtained with good reproducibility and stability. Furthermore, the mechanism of chiral recognition was investigated using molecular docking with AutoDock. Docking results showed that the enantioselectivity factor rather than resolution is correlated with the binding free energy difference between enantiomers with the chiral covalent organic framework. And abundant acetoxy and nitrile groups as well as benzene rings in the chiral covalent organic framework are responsible for the enantioseparation ability of the chiral monolithic capillary columns.

Dual-Signaling Photoelectrochemical Biosensor Based on Biocatalysis-Induced Vulcanization of Bi2MoO6 Nanosheets.

A magnetic-assisted photoelectrochemical (PEC) and colorimetric (CL) dual-modal biosensing platform with high precision was established to monitor prostate-specific antigen (PSA) based on Bi2MoO6 nanosheets (BMO) by coupling the aptamer-guided hybridization chain reaction (HCR) with the hydrolysate-induced vulcanization reaction of Bi2MoO6 nanosheets. Upon addition of PSA, trigger DNA (tDNA) was released by the interaction between the target analyte and the aptamer and then further hybridized with anchor DNA (aDNA) conjugated on magnetic beads (MBs). The as-released tDNA initiated the target-assisted HCR in the presence of two alternating hairpin sequences (Bio-H1 and Bio-H2) to produce nicked long double-stranded DNA on the surface of MBs, where numerous alkaline phosphatase (ALP) enzymes could assemble with MBs through the biotin-avidin reaction, resulting in the hydrolysis of sodium thiophosphate (TP) to H2S. The as-produced H2S reacted with BMO to form vulcanized BMO (BMO-S), thus leading to obvious enhanced PEC performance under visible light with the color change from light yellow to brown. Having optimized the test conditions, the magnetic-assisted biosensing system holds a good quantitative diagnosis sensitivity area in a range of 5.0 pg mL-1-100 ng mL-1 with a calculated detection limit down to 3.5 pg mL-1. Meanwhile, a visual colorimetric assay on basis of the change in the color of the materials was also realized. Given the exceptional performance of the constructed biosensor, it may possess great promise as an advanced bioanalytical tool for practical applications.

Dual-Channel Photoelectrochemical Ratiometric Aptasensor with up-Converting Nanocrystals Using Spatial-Resolved Technique on Homemade 3D Printed Device.

A near-infrared light-activated ratiometric photoelectrochemical aptasensor was fabricated for detection of carcinoembryonic antigen (CEA) coupling with upconversion nanoparticles (UCNPs)-semiconductor nanocrystals-based spatial-resolved technique on a homemade 3D printing device in which a self-regulating integrated electrode was designed for dual signal readout. The as-prepared NaYF4:Yb,Er UCNPs@CdTe nanocrystals were initially assembled on two adjacent photoelectrodes, then CEA aptamer 1 (A1) and capture DNA (CA) were modified onto two working photoelectrodes (WP1 and WP2) through covalent binding, respectively, and then gold nanoparticle-labeled CEA aptamer 2 (Au NP-A2) was immobilized on the surface of functional WP2 for the formation of double-stranded DNA. Upon target CEA introduction, the various concentrations of CEA were captured on the WP1, whereas the binding of the CEA with Au NP-A2 could be released from the WP2 thanks to the highly affinity of CEA toward A2. The dual signal readout with the "signal-off" of WP1 and "signal-on" of WP2 were employed for the spatial-resolved PEC (SR-PEC) strategy to detect CEA as an analytical model. Combining NaYF4:Yb,Er UCNPs@CdTe nanocrystals with spatial-resolved model on 3D printing device, the PEC ratiometric aptasensor based on steric hindrance effect and exciton-plasmon interactions (EPI) exhibited a linear range from 10.0 pg mL-1 to 5.0 ng mL-1 with a limit of detection of 4.8 pg mL-1 under 980 nm illumination. The SR-PEC ratiometric strategy showed acceptable stability and reproducibility with a superior anti-interference ability. This approach can provide the guidance for the design of ratiometric, multiplexed, and point-of-care biosensors.

NaYF4:Yb,Er Upconversion Nanotransducer with in Situ Fabrication of Ag2S for Near-Infrared Light Responsive Photoelectrochemical Biosensor.

An innovative near-infrared (NIR) light-driven photoelectrochemical (PEC) aptasensor was constructed for sensitive screening of carcinoembryonic antigen (CEA) on the basis of in situ formation of Ag2S nanoparticles on the NaYF4:Yb,Er upconversion nanoparticles (UCNs), coupled with hybridization chain reaction (HCR) for the signal amplification. Utilization of UCN as the light nanotransducer could convert the NIR light into an applicable wavelength harvested by semiconductors. The multiemissions of NaYF4:Yb,Er UCN could match well with the absorption characteristics of Ag2S. In the presence of target CEA, a sandwich-type reaction was carried out between capture CEA aptamer/NaYF4:Yb,Er-modified electrode and trigger CEA aptamer, which underwent an unbiased strand-displacement reaction to open C-rich hairpin probes in sequence between two alternating hairpins with the assistance of C-Ag+-C chelation reaction. Upon addition of sulfide, the chelated Ag+ ions in the long-nicked DNA poly strands by hybridization chain reaction reacted with sulfide to generate Ag2S nanoparticles. The formed Ag2S could utilize effectively the upconversion emissions to amplify the photocurrent. Under optimal conditions, NaYF4:Yb,Er-based NIR light-responsive PEC aptasensing platform exhibited high sensitivity for the determination of CEA within a dynamic linear range of 0.005-5.0 ng mL-1. The limit of detection was 1.9 pg mL-1. Good precision and high specificity could be acquired in this system for the analysis of target CEA. Human serum samples containing target CEA were measured using our strategy and received well-matched results relative to human CEA enzyme-linked immunosorbent assay kits. Importantly, the NaYF4:Yb,Er-based NIR light-responsive PEC aptasensing system provides a new ideal for the detection of disease-related biomarkers using a nucleic acid-based amplification strategy.

Self-Referenced Smartphone Imaging for Visual Screening of H2S Using Cu xO-Polypyrrole Conductive Aerogel Doped with Graphene Oxide Framework.

Cu xO-polypyrrole conductive aerogel loaded on graphene oxide framework (Cu xO-PPy@GO) with a three-dimensional (3D) porous architecture was utilized for high-efficient visual screening of H2S on a flexible paper substrate. The detectable signal was acquired on a portable smartphone by using a self-referenced imaging platform equipped with the light emitting diode (LED) accompanying an image processing. As a proof-of-concept, Cu xO-PPy@GO aerogel-based sensing strategy was also developed for Na2S detection and egg spoilage monitoring. Such a flexible paper-supported sensor is expected for potential application in portable and wearable food-safety fields.

Near-Infrared-to-Ultraviolet Light-Mediated Photoelectrochemical Aptasensing Platform for Cancer Biomarker Based on Core-Shell NaYF4:Yb,Tm@TiO2 Upconversion Microrods.

Titanium dioxide (TiO2; as a potential photosensitizer) has good photocurrent performance and chemical stability but often exhibits low utilization efficiency under ultraviolet (UV) region excitation. Herein, we devised a near-infrared light-to-UV light-mediated photoelectrochemical (PEC) aptasensing platform for the sensitive detection of carcinoembryonic antigen (CEA) based on core-shell NaYF4:Yb,Tm@TiO2 upconversion microrods by coupling with target-triggered rolling circle amplification (RCA). The upconversion microrods synthesized through the hydrothermal reaction could act as a photosensing platform to convert the near-infrared (near-IR) excitation into UV emission for generation of photoinduced electrons. The target analyte was determined on a functional magnetic bead by using the corresponding aptamers with a sandwich-type assay format. Upon target CEA introduction, a complex was first formed between capture aptamer-1-conjugated magnetic bead (Apt1-MB) and aptamer-2-primer DNA (Apt2-pDNA). Thereafter, the carried primer DNA by the aptamer-2 paired with linear padlock DNA to trigger the RCA reaction. The guanine (G)-rich product by RCA reaction was cleaved by exonuclease I and exonuclease III (Exos I/III), thereby resulting in the formation of numerous individual guanine bases to enhance the photocurrent of core-shell NaYF4:Yb,Tm@TiO2 upconversion microrods under near-IR illumination (980 nm). Under optimal conditions, the near-IR light-mediated PEC aptasensing system could exhibit good photoelectrochemical response toward target CEA and allowed for the detection of target CEA as low as 3.6 pg mL-1. High reproducibility and good accuracy were achieved for analysis of human serum specimens. Importantly, the near-IR-activated PEC aptasensing scheme provides a promising platform for ultrasensitive detection of other biomolecules.

Plasmonic Enhancement Coupling with Defect-Engineered TiO2-x: A Mode for Sensitive Photoelectrochemical Biosensing.

This work demonstrates that the photoelectric response of defect-engineered TiO2-x modified with Au nanoparticles can be modulated by oxygen vacancy concentration and excitation wavelength. When strongly plasmonic Au nanoparticles are anchored to defect-engineered TiO2-x by DNA hybridization, several times plasmonic enhancement of photocurrent occurs under 585 nm excitation, and it is employed as a novel signaling mode for developing an improved photoelectrochemical sensing platform. This signaling mode combined with exonuclease III-assisted target recycling amplification exhibits excellent analytical performance, which provides a novel photoelectrochemical detection protocol.

Bioresponsive Release System for Visual Fluorescence Detection of Carcinoembryonic Antigen from Mesoporous Silica Nanocontainers Mediated Optical Color on Quantum Dot-Enzyme-Impregnated Paper.

An all-in-one paper-based analytical device (PAD) was successfully developed for visual fluorescence detection of carcinoembryonic antigen (CEA) on CdTe/CdSe quantum dot (QD)-enzyme-impregnated paper by coupling with a bioresponsive controlled-release system from DNA-gated mesoporous silica nanocontainers (MSNs). The assay was carried out in a centrifuge tube by using glucose-loaded MSNs with a CEA aptamer and a QD-enzyme-paper attached on the lid. Initially, single-strand complementary DNA to a CEA aptamer was covalently conjugated to the aminated MSN, and then glucose (enzyme substrate) molecules were gated into the pore with the help of the aptamer. Glucose oxidase (GOD) and CdTe/CdSe QDs were coimmobilized on paper for the visual fluorescence signal output. Upon target CEA introduction in the detection cell, the analyte specifically reacted with the immobilized aptamer on the MSN to open the pore, thereby resulting in the glucose release. The released glucose was oxidized by the immobilized GOD on paper to produce gluconic acid and hydrogen peroxide, and the latter quenched the fluorescence of CdTe/CdSe QDs, which could be determined by the naked eye on a portable smartphone and a commercial fluorospectrometer. Under optimal conditions, the PAD-based sensing system enabled sensitive discrimination of target CEA against other biomarkers or proteins in a linear range of 0.05-20 ng mL-1 with a limit of detection of 6.7 pg mL-1 (ppt). In addition, our strategy displayed high specificity, good reproducibility, and acceptable accuracy for analyzing human serum specimens with a commercial human CEA ELISA kit. Importantly, this methodology offers promise for simple analysis of biological samples and is suitable for use in the mass production of miniaturized devices, thus opening new opportunities for protein diagnostics and biosecurity.

Cu2+-Doped SnO2 Nanograin/Polypyrrole Nanospheres with Synergic Enhanced Properties for Ultrasensitive Room-Temperature H2S Gas Sensing.

The organic-inorganic nanohybrids are emerging as one of the most attractive sensing materials in the area of gas sensors and usually exhibit some advanced properties because of synergetic/complementary effects between organic molecules and inorganic components. This work demonstrates a novel class of organic-inorganic nanohybrids, Cu2+-doped SnO2 nanograin/poly pyrrole nanospheres, for the sensitive room-temperature H2S gas sensing. Doping Cu2+ in SnO2 nanograins remarkably enhances the surface potential barrier by tailoring surface defects. After polymerizing pyrrole surrounded nanograins in aqueous media to form the organic-inorganic nanohybrids, the resulting nanoheterojunctions further improve the sensitivity. Additionally, the nanohybrids-based sensor provides high surface area and abounding reaction sites to accelerate gas diffusion and adsorption as well as the electron transfer. Compare with pristine SnO2 nanograins alone, the sensitivity of using the nanohybrids increases 7 times for the detection of 50-ppm of H2S. The response and recovery rate can increase 27 and 22 times at room temperature, respectively. Significantly, this work provides an attractive material for the real-time monitoring of H2S, whereas the insights into organic-inorganic composite interactions within the sensing mechanism may pave the way for designing functional materials with tailored properties.

Semiautomated Support Photoelectrochemical Immunosensing Platform for Portable and High-Throughput Immunoassay Based on Au Nanocrystal Decorated Specific Crystal Facets BiVO4 Photoanode.

Photoelectrochemical (PEC) measurement has been developed rapidly for bioanalysis in recent years. However, the actual application for most existed PEC bioanalytical systems is still a challenge because the perfect solutions for sensing surface design, high-throughput detection, and portability are lacked. To successfully overcome these limitations and realize accurate, continuous screening and assessing on prognostic indicator of early stage cancer on the spot, an innovative and portable semiautomated support power-free photoelectrochemical (SP-PEC) immunosensing platform consisted with a miniature semiautomatic injection system and digital multimeter (DMM) readout is designed (prostate specific antigen, PSA, was used as the proof-of-concept analyte). Decahedral BiVO4 that decorated with Au nanocrystal on {010} facets (Au-BiVO4) by photodeposition is used as the photoanode materials to produce photocurrent signal under irradiation of micro laser light (5.0 w, λ ≥ 380 nm). The monoclonal anti-PSA capture antibody (mAb1)-functionalized Fe3O4 magnetic nanobeads (mAb1-MN) and glucose oxidase (GOx)/monoclonal detection antibody (mAb2)-conjugated gold nanoparticle (GOx-AuNP-mAb2) are employed as immunosensing probe and signal probe, respectively. The H2O2 as an excellent holes scavenger that in suit generated from GOx oxidization glucose substrate significantly amplifies the photocurrent. The variation of instantaneous current value that registered as the signal of the immunoassay increases linearly with the logarithm of target PSA concentration increasing in a wide range from 10 pg mL-1 to 100 ng mL-1 with a low detection limit (LOD) of 4.0 pg mL-1. The SP-PEC immunosensing platform not only simplifies the assay process, but also improves detecting efficiency. The semiautomatic and portable SP-PEC analysis device allows analysis on spot and high-throughput continuous detection. Additional, we also gain deep insight into the relations between the specific shape as well as Au nanocrystal decoration and PEC activity and speculate the possible enhancement mechanisms of Au-BiVO4. Therefore, the present work not only develops a flexible SP-PEC biosensor platform for rapid and continuous detection, but also provides a possible route for designing high performance photoelectric materials.

Magnetic Graphene Nanosheet-Based Microfluidic Device for Homogeneous Real-Time Electronic Monitoring of Pyrophosphatase Activity Using Enzymatic Hydrolysate-Induced Release of Copper Ion.

A novel flow-through microfluidic device based on a magneto-controlled graphene sensing platform was designed for homogeneous electronic monitoring of pyrophosphatase (PPase) activity; enzymatic hydrolysate-induced release of inorganic copper ion (Cu(2+)) from the Cu(2+)-coordinated pyrophosphate ions (Cu(2+)-PPi) complex was assessed to determine enzyme activity. Magnetic graphene nanosheets (MGNS) functionalized with negatively charged Nafion were synthesized by using the wet-chemistry method. The Cu(2+)-PPi complexes were prepared on the basis of the coordination reaction between copper ion and inorganic pyrophosphate ions. Upon target PPase introduction into the detection system, the analyte initially hydrolyzed pyrophosphate ions into phosphate ions and released the electroactive copper ions from Cu(2+)-PPi complexes. The released copper ions could be readily captured through the negatively charged Nafion on the magnetic graphene nanosheets, which could be quantitatively monitored by using the stripping voltammetry on the flow-through detection cell with an external magnet. Under optimal conditions, the obtained electrochemical signal exhibited a high dependence on PPase activity within a dynamic range from 0.1 to 20 mU mL(-1) and allowed the detection at a concentration as low as 0.05 mU mL(-1). Coefficients of variation for reproducibility of the intra-assay and interassay were below 7.6 and 9.8%, respectively. The inhibition efficiency of sodium fluoride (NaF) also received good results in pyrophosphatase inhibitor screening research. In addition, the methodology afforded good specificity and selectivity, simplification, and low cost without the need of sample separations and multiple washing steps, thus representing a user-friendly protocol for practical utilization in a quantitative PPase activity.

Enzymatic Oxydate-Triggered Self-Illuminated Photoelectrochemical Sensing Platform for Portable Immunoassay Using Digital Multimeter.

Herein a novel split-type photoelectrochemical (PEC) immunosensing platform was designed for sensitive detection of low-abundance biomarkers (prostate-specific antigen, PSA, used in this case) by coupling a peroxyoxalate chemiluminescence (PO-CL) self-illuminated system with digital multimeter (DMM) readout. The PEC detection device consisted of a capacitor/DMM-joined electronic circuit and a PO-CL-based self-illuminated cell. Initially, reduced graphene oxide-doped BiVO4 (BiVO4-rGO) photovoltaic materials with good photoelectric properties was integrated into the capacitor/DMM-joined circuit for photocurrent generation in the presence of hydrogen peroxide (H2O2, as the hole-trapping reagent). A sandwich-type immunoreaction with target PSA was carried out in capture antibody-coated microplates by using glucose oxidase/detection antibody-conjugating gold nanoparticle (pAb2-AuNP-GOx). Accompanying the sandwiched immunocomplex, the labeled GOx could oxidize glucose to produce H2O2. The as-generated H2O2 could act as the coreaction reagent to trigger the chemiluminescence of the peroxyoxalate system and the PEC reaction of the BiVO4-rGO. Meanwhile, the self-illuminated light could induce photovoltaic material (BiVO4-rGO) to produce a voltage that was utilized to charge an external capacitor. With the switch closed, the capacitor could discharge through the DMM and provide an instantaneous current. Different from conventional PEC immunoassays, the as-generated photoelectron was stored in the capacitor and released instantaneously to amplify the photocurrent. Under the optimal conditions, the transient current increased with the increasing target PSA concentration in the dynamic working range from 10 pg mL(-1) to 80 ng mL(-1) with a detection limit (LOD) of 3 pg mL(-1). This work demonstrated for the first time that the peroxyoxalate CL system could be used as a suitable substitute of physical light source to apply in PEC immunoassay. In addition, this methodology afforded good reproducibility, precision, and high specificity, and the method accuracy matched well with the commercial PSA ELISA kit. Importantly, the developed split-type photoelectrochemical immunoassay could not only avoid the interfering of the biomolecules relative to the photovoltaic materials but also eliminate the need of an exciting light source and expensive instrumentation, thus representing a user-friendly and low-cost assay protocol for practical utilization in quantitative low-abundance proteins.

Portable glucose sensing analysis based on laser-induced graphene composite electrode.

In this work, a portable electrochemical glucose sensor was studied based on a laser-induced graphene (LIG) composite electrode. A flexible graphene electrode was prepared using LIG technology. Poly(3,4-ethylene dioxythiophene) (PEDOT) and gold nanoparticles (Au NPs) were deposited on the electrode surface by potentiostatic deposition to obtain a composite electrode with good conductivity and stability. Glucose oxidase (GOx) was then immobilized using glutaraldehyde (GA) to create an LIG/PEDOT/Au/GOx micro-sensing interface. The concentration of glucose solution is directly related to the current value by chronoamperometry. Results show that the sensor based on the LIG/PEDOT/Au/GOx flexible electrode can detect glucose solutions within a concentration range of 0.5 × 10-5 to 2.5 × 10-3 mol L-1. The modified LIG electrode provides the resulting glucose sensor with an excellent sensitivity of 341.67 µA mM-1 cm-2 and an ultra-low limit of detection (S/N = 3) of 0.2 × 10-5 mol L-1. The prepared sensor exhibits high sensitivity, stability, and selectivity, making it suitable for analyzing biological fluid samples. The composite electrode is user-friendly, and can be built into a portable biosensor device through smartphone detection. Thus, the developed sensor has the potential to be applied in point-of-care platforms such as environmental monitoring, public health, and food safety.

Foldable paper-based photoelectrochemical biosensor based on etching reaction of CoOOH nanosheets-coated laser-induced PbS/CdS/graphene for sensitive detection of ampicillin.

Timely and rapid detection of antibiotic residues in the environment is conducive to safeguarding human health and promoting an ecological virtuous cycle. A foldable paper-based photoelectrochemical (PEC) sensor was successfully developed for the detection of ampicillin (AMP) based on glutathione/zirconium dioxide hollow nanorods/aptamer (GSH@ZrO2 HS@apt) modified cellulose paper as a reactive zone with laser direct-writing lead sulfide/cadmium sulfide/graphene (PbS/CdS/LIG) as photoelectrode and cobalt hydroxide (CoOOH) as a photoresist material. Initially, AMP was introduced into the paper-based reaction zone as a biogate aptamer, which specifically recognized the target and then left the ZrO2 HS surface, releasing glutathione (GSH) encapsulated inside. Subsequently, the introduction of GSH into the reaction region and etching of CoOOH nanosheets to expose the PbS/CdS/LIG photosensitive material increased photocurrent. Under optimal conditions, the paper-based PEC biosensor showed a linear response to AMP in the range of 5.0 - 2 × 104 pM with a detection limit of 1.36 pM (S/N = 3). In addition, the constructed PEC sensing platform has excellent selectivity, high stability and favorable reproducibility, and can be used to assess AMP residue levels in various real water samples (milk, tap water, river water), indicating its promising application in environmental antibiotic detection.

A laser-induced zinc oxide/graphene photoelectrode for a photocurrent-polarity-switching photoelectrochemical biosensor with bipedal DNA walker amplification.

A photocurrent-polarity-switching photoelectrochemical (PEC) biosensor was developed for the ultrasensitive detection of tobramycin (TOB) through bipedal DNA walker amplification with hemin-induced photocurrent-polarity-switching using a laser-induced zinc oxide/graphene (ZnO/LIG) photoelectrode. Specifically, the ZnO/LIG photoelectrode was synthesized in situ by a laser direct writing (LDW) technique. In the presence of TOB, it reacted with HP1 and HP2 and the DNA walker response was activated to form a stable hemin/G-quadruplex. Furthermore, hemin induced a polarity shift in the photocurrent signal. The developed analytical platform exhibited excellent photoelectron transport performance of ZnO/LIG, the signal amplification effect of the DNA walker strategy, and the photocurrent-polarity-switching ability of hemin. Therefore, it demonstrated satisfying photocurrent responses to the target TOB within the working range of 20 nM-1.0 µM at a low detection limit of 5.43 nM. The PEC platform exhibited good stability, reproducibility, sufficient sensitivity and high selectivity for complex experimental samples. Moreover, the photocurrent-polarity-switching PEC biosensor improved the anti-interference ability and avoided false positives or negatives.

MXene-TiO2-based photocatalytic fuel cell with bioresponsive controlled glucose release system: An innovative mode for Ochratoxin A detection.

Self-powered photocatalytic fuel cell (PFC)-based sensors incorporating bioelement recognition with fuel concentration-dependent output power have been developed for electrochemical analysis, but most involve poor energy conversion efficiency and are unsuitable for routine use. Herein, a self-powered and self-checking PFC bioanalysis platform under visible light for ultrasensitive screening of Ochratoxin A (OTA) was designed. Specifically, the self-powered photocatalytic fuel cell-based sensor was comprised of a photoanode fabricated with MXenes (Ti3C2)-TiO2 and a cathode modified with Prussian blue (PB). To realize the high-performance of OTA detection, mesoporous silica nanoparticles (MSNs) were used as nanocontainers to load glucose, and aptamers were assembled on the surface of MSNs as dual-gated molecules to form signal probes. The reaction of analyte OTA with OTA aptamer was greater than the force between OTA aptamer and MSN, resulting in the release of glucose from MSNs. The released glucose was photo-oxidized by Ti3C2-TiO2 under visible light illumination and used as an electron acceptor to reduce PB, resulting in a high cell output response with a maximum output power (Pmax) of 23.516 µW cm-2. Meanwhile, the electrochromic PB enabled colorimetric detection of OTA with self-checking. The self-powered Ti3C2-TiO2-based PFC with target-recognition cargo release system exhibited superior analytical performance toward OTA in the range of 0.2 ppb-20 ppb and limit of detection (LOD) down to 0.0587 ppb. Additionally, excellent stability, rapid response, and exquisite selectivity for real samples (beer) was acceptable, providing an efficient approach in food safety monitoring.

Ti3C2 MXene-anchored photoelectrochemical detection of exosomes by in situ fabrication of CdS nanoparticles with enzyme-assisted hybridization chain reaction.

Exosomes that carry large amounts of tumor-specific molecular information have been identified as a potential non-invasive biomarker for early warning of cancer. In this work, we reported an enzyme-assisted photoelectrochemical (PEC) biosensor for quantification of exosomes based on the in situ synthesis of Ti3C2 MXene/CdS composites with magnetic separation technology and hybridization chain reaction (HCR). First, exosomes were specifically bound between aptamer-labeled magnetic beads (CD63-MBs) and a cholesterol-labeled DNA anchor. The properly designed anchor ends acted as a trigger to enrich the alkaline phosphatase (ALP) through HCR. It catalyzed more sodium thiophosphate to generate the sulfideion (S2-), which combined with Cd2+ for in situ fabrication of CdS on Ti3C2 MXene resulting in elevated photocurrent. The Ti3C2 MXene-anchored PEC method was realized for the quantitative detection of exosomes, which exhibited the dynamic working range from 7.3 × 105 particles per mL to 3.285 × 108 particles per mL with a limit of detection of 7.875 × 104 particles per mL. The strategy showed acceptable stability, high sensitivity, rapid response and excellent selectivity. Furthermore, we believe that the PEC biosensor has huge potential as a routine bioassay method for the precise quantification of exosomes from breast cancer in the future.

Smartphone-Based Photoelectrochemical Immunoassay with Co9S8@ZnIn2S4 for Point-of-Care Diagnosis of Breast Cancer Biomarker.

Photoelectrochemical immunoassays incorporating specific antigen-antibody recognition reactions with the photon-electron conversion capabilities of photocatalysts have been developed for biomarker detection, but most involve bulky and expensive equipment and are unsuitable for point-of-care testing. Herein, a portable smartphone-based photoelectrochemical immunoassay was innovatively designed for the on-site detection of breast cancer biomarkers (human epidermal growth factor receptor 2; HER2). The system consists of a split-type immunoassay mode, disposable screen-printed electrode covered with hierarchical Co9S8@ZnIn2S4 heterostructures, an integrated circuit board, and a Bluetooth smartphone equipped with a specially designed app. Using alkaline phosphatase (ALP) catalytic strategy to in situ generate ascorbic acid (AA) for electron-donating toward Co9S8@ZnIn2S4 heterostructures, an immunoreaction was successfully constructed for the HER2 detection in the real sample due to the positive correlation of the photocurrent signal to electron donor concentration. Differential charge density indicates that the formation of Co9S8@ZnIn2S4 heterojunction can facilitate the flow of charges in the interface and enhance the photocurrent of the composite. More importantly, the measured photocurrent signal can be wirelessly transmitted to the software and displayed on the smartphone screen to obtain the corresponding HER2 concentration value. The photocurrent values linearly with the logarithm of HER2 concentrations range spanned from 0.01 ng/mL to 10 ng/mL with a detection limit of 3.5 pg/mL. Impressively, the clinical serum specimen results obtained by the proposed method and the wireless sensing device are in good agreement with the enzyme-linked immunosorbent assay (ELISA).

Nanostructure-based photoelectrochemical sensing platforms for biomedical applications.

As a newly developed and powerful analytical method, the use of photoelectrochemical (PEC) biosensors opens up new opportunities to provide wide applications in the early diagnosis of diseases, environmental monitoring and food safety detection. The properties of diverse photoactive materials are one of the essential factors, which can greatly impact the PEC performance. The continuous development of nanotechnology has injected new vitality into the field of PEC biosensors. In many studies, much effort on PEC sensing with semiconductor materials is highlighted. Thus, we propose a systematic introduction to the recent progress in nanostructure-based PEC biosensors to exploit more promising materials and advanced PEC technologies. This review briefly evaluates the several advanced photoactive nanomaterials in the PEC field with an emphasis on the charge separation and transfer mechanism over the past few years. In addition, we introduce the application and research progress of PEC sensors from the perspective of basic principles, and give a brief overview of the main advances in the versatile sensing pattern of nanostructure-based PEC platforms. This last section covers the aspects of future prospects and challenges in the nanostructure-based PEC analysis field.

A chemiresistive thin-film translating biological recognition into electrical signals: an innovative signaling mode for contactless biosensing.

An innovative signaling mode in which a chemiresistive thin-film electrode monitors the specific gaseous component that results from a biological recognition event to indirectly detect targets in the liquid phase is developed for highly-efficient contactless biosensing. This signaling mode may open a new horizon in designing robust biosensing devices for bioanalysis.