Electropolymerization-Induced Positively Charged Phenothiazine Polymer Photoelectrode for Highly Sensitive Photoelectrochemical Biosensing

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.

Advances on chalcogenide quantum dots-based sensors for environmental pollutants monitoring

Water contamination represents a significant ecological impact with global consequences, contributing to water scarcity worldwide. The presence of several pollutants, including heavy metals, pharmaceuticals, pesticides, and pathogens, in water resources underscores a pressing global concern, prompting the European Union (EU) to establish a Water Watch List to monitor the level of these substances. Nowadays, the standard methods used to detect and quantify these contaminants are mainly liquid or gas chromatography coupled with mass spectrometry (LC/GC-MS). While these methodologies offer precision and accuracy, they require expensive equipment and experienced technicians, and cannot be used on the field. In this context, chalcogenide quantum dots (QDs)-based sensors have emerged as promising, user-friendly, practical, and portable tools for environmental monitoring. QDs are semiconductor nanocrystals that possess excellent properties, and have demonstrated versatility across various sensor types, such as fluorescent, electrochemical, plasmonic, and colorimetric ones. This review summarizes recent advances (2019-2023) in the use of chalcogenide QDs for environmental sensing, highlighting the development of sensors capable of detect efficiently heavy metals, anions, pharmaceuticals, pesticides, endocrine disrupting compounds, organic dyes, toxic gases, nitroaromatics, and pathogens.

Self-powered molecularly imprinted photoelectrochemical sensor based on Ppy/QD/HOF heterojunction for the detection of bisphenol A

As an emerging porous material, hydrogen-bonded organic framework materials (HOFs) still pose application challenges. In this work, the designed type "I + II" heterojunction extracted hot electrons from HOFs using quantum dots (QDs) and polypyrrole (Ppy), improving the stability and photoelectrochemical performance of materials. In addition to serving as a potential well, electropolymerized Ppy was used as a recognition element for bisphenol A (BPA), and a novel self-powered molecularly imprinted photoelectrochemical (MIP-PEC) sensor was designed. The sensing platform showed a linear relationship from 1 × 10-10 to 1 × 10-7 mol∙L-1 and from 1 × 10-7 to 1 mol∙L-1 with an acceptable detection limit of 4.2 × 10-11 mol∙L-1. This is the first application of HOFs in constructing MIP-PEC sensors and a new attempt to improve the stability of HOFs for the application of porous crystal materials in the sensing field.

A supramolecular electrochemical probe based on a tetrazole derivative pillar[5]arene/methylene blue system

For the first time, an original synthetic approach has been developed that enables the introduce ten tetrazole fragments into the pillar[5]arene structure. A supramolecular electrochemical probe was assembled for the first time from the obtained macrocycles and an electrochemically active signal converter: methylene blue (MB) dye. The ability of pillar[5]arene containing tetrazole fragments to selectively bind MB was confirmed by UV-vis and 2D 1H-1H NOESY spectroscopy. The stoichiometry of the resulting pillar[5]arene/MB complex = 1 : 2. This new supramolecular probe pillar[5]arene/MB allowed the detection of changes in the electrochemical signals of MB implemented in the supramolecular complex depending on the presence or absence of some metal ions (Zn2+ and Co2+) that do not exert their own redox activity. This will find further applications for the enhancement of the range of analytes detected by their influence on host-guest complexation and for the design of biosensors based on specific DNA-MB interactions.

High performance photoelectrochemical immunosensing platform based on front-illuminated Mo:BiVO4 photoelectrodes for procalcitonin assay

The outstanding photoactive materials are the imperative for the construction of a front-illuminated photoelectrochemical (PEC) biosensor, which is crucial step for improving the detection sensitivity. Yet, the weak and unstable initial PEC signals of the photoelectrodes have limited evidently the detection performance. Herein, a front-illuminated "on-off" PEC immunosensor was constructed based on Mo:BiVO4 as photoactive matrix and Au/CeO2 as signal quencher for sensitive detection of procalcitonin (PCT). Systematic studies reveal that the Mo doped BiVO4 can increase the charge carrier density of BiVO4, leading to much higher initial signal under front illumination than back illumination. Moreover, Mo:BiVO4 was directly grown on conducting substrates, which effectively overcomes the loose combination of sensing substrate ensuring good electrical contact and continuity. Upon coupling with Au/CeO2 as signal quencher, the initial photocurrent signal can be significantly quenched. As a result, the proposed PEC immunosensor presents a wide linear range from 10 fg mL-1 to 50 ng mL-1 with a detection limit of 2.45 fg mL-1. Impressively, this study will open a new avenue for the construction of highly efficient and stable photoelectrode, as well as extend the application of PEC biosensor for biomarkers detection in early disease diagnosis.

One-step electrodeposited hybrid nanofilms in amperometric biosensor development

This review summarizes recent developments in amperometric biosensors, based on one-step electrodeposited organic-inorganic hybrid layers, used for analysis of low molecular weight compounds. The factors affecting self-assembly of one-step electrodeposited films, methods for verifying their composition, advantages, limitations and approaches affecting the electroanalytical performance of amperometric biosensors based on organic-inorganic hybrid layers were systemized. Moreover, issues related to the formation of one-step organic-inorganic hybrid functional layers with different structures in biosensors produced under the same electrodeposition parameters are discussed. The systemized dependencies can support the preliminary choice of functional sensing layers with architectures tuned for specific biotechnology and life science applications. Finally, the capabilities of one-step electrodeposition of organic-inorganic hybrid functional films beyond amperometric biosensors were highlighted.

Nanozyme-Enhanced Electrochemical Biosensors: Mechanisms and Applications

Nanozymes, as innovative materials, have demonstrated remarkable potential in the field of electrochemical biosensors. This article provides an overview of the mechanisms and extensive practical applications of nanozymes in electrochemical biosensors. First, the definition and characteristics of nanozymes are introduced, emphasizing their significant role in constructing efficient sensors. Subsequently, several common categories of nanozyme materials are delved into, including metal-based, carbon-based, metal-organic framework, and layered double hydroxide nanostructures, discussing their applications in electrochemical biosensors. Regarding their mechanisms, two key roles of nanozymes are particularly focused in electrochemical biosensors: selective enhancement and signal amplification, which crucially support the enhancement of sensor performance. In terms of practical applications, the widespread use of nanozyme-based electrochemical biosensors are showcased in various domains. From detecting biomolecules, pollutants, nucleic acids, proteins, to cells, providing robust means for high-sensitivity detection. Furthermore, insights into the future development of nanozyme-based electrochemical biosensors is provided, encompassing improvements and optimizations of nanozyme materials, innovative sensor design and integration, and the expansion of application fields through interdisciplinary collaboration. In conclusion, this article systematically presents the mechanisms and applications of nanozymes in electrochemical biosensors, offering valuable references and prospects for research and development in this field.

A high-performance photoelectrochemical sensor based on CdS-Au composite nanomaterials and localized surface plasmon resonance for ultrasensitive detection of ascorbic acid

Ascorbic acid (AA), which plays a vital role in the metabolism of the human body, is closely correlated with various diseases, including rheumatoid arthritis, scurvy, Parkinson's disease, urinary stones, and diarrhea. The detection of AA is of great significance for early prevention and diagnosis of related diseases. In this paper, a high-performance photoelectrochemical (PEC) sensor was constructed based on cadmium sulfide-gold (CdS-Au) composite nanomaterials for ultrasensitive ascorbic acid (AA) detection. Due to the localized surface plasmon resonance (LSPR) effect of gold nanoparticles (AuNPs), the PEC performance of CdS-Au composite nanomaterials was significantly improved compared to CdS semiconductor nanomaterials. Under the optimal conditions, the AA concentration was linearly related to the photocurrent signal in the range of 0.01 μM-200 μM, with the detection limit being 0.2 nM (S/N = 3) and the sensitivity being 642.9 μA mM-1 cm-2. In addition, the mechanism of the PEC sensor based on CdS-Au composite nanomaterials for ultrasensitive AA detection was discussed. Lastly, the self-constructed PEC sensors have been successfully applied in detecting AA in vitamin C tablets and actual blood samples, meeting the detection criteria required by the Chinese Pharmacopoeia (CP, 2020 edition). The self-fabricated PEC sensors in this paper are expected to be used for quality assessment of AA-related drugs and diagnosis of relevant diseases.

Photocurrent Polarity Switchable Sensing of Hyaluronidase Activity by Regulating Electrostatic Interactions between Two Semiconductors

Photocurrent polarity switchable photoelectrochemical (PEC) sensing has superior accuracy and anti-interference ability to conventional PEC sensing. The development of a novel strategy for photocurrent polarity switchable sensing is of great interest. Herein, a novel strategy for photocurrent polarity switchable sensing is reported by regulating electrostatic interactions between two semiconductor photoactive materials. Hyaluronic acid (HA)-modified CuO nanosheets show a negatively charged surface, which prevents the attachment of CuO nanosheets to negatively charged CdS nanodendrite-modified photoelectrodes because of the strong electrostatic repulsion. In the presence of hyaluronidase (HAase), the specific hydrolysis of HA on the surface of CuO by HAase can yield a positively charged surface, so CuO can be attached to a CdS-modified photoelectrode via electrostatic attraction, leading to photocurrent polarity switching. The photocurrent polarity switchable detection of HAase activity is achieved with an ultralow detection limit of 2 × 10-3 U mL-1 and a wide linear detection range between 0.01 and 100 U mL-1. This work provides a new and effective photocurrent polarity switching strategy for PEC sensing and a simple and efficient method for detecting HAase activity.

Semiconductor quantum dots in photoelectrochemical sensors from fabrication to biosensing applications

Semiconductor quantum dots (QDs) are a promising class of nanomaterials for developing new photoelectrodes and photoelectrochemistry systems for energy storage, transfer, and biosensing applications. These materials have unique electronic and photophysical properties and can be used as optical nanoprobes in displays, biosensors, imaging, optoelectronics, energy storage and energy harvesting. Researchers have recently been exploring the use of QDs in photoelectrochemical (PEC) sensors, which involve exciting a QD-interfaced photoactive material with a flashlight source and generating a photoelectrical current as an output signal. The simple surface properties of QDs also make them suitable for addressing issues related to sensitivity, miniaturization, and cost-effectiveness. This technology has the potential to replace current laboratory practices and equipment, such as spectrophotometers, used for testing sample absorption and emission. Semiconductor QD-based PEC sensors offer simple, fast, and easily miniaturized sensors for analyzing a variety of analytes. This review summarizes the various strategies for interfacing QD nanoarchitectures for PEC sensing, as well as their signal amplification. PEC sensing devices, particularly those used for the detection of disease biomarkers, biomolecules (glucose, dopamine), drugs, and various pathogens, have the potential to revolutionize the biomedical field. This review discusses the advantages of semiconductor QD-based PEC biosensors and their fabrication methods, with a focus on disease diagnostics and the detection of various biomolecules. Finally, the review provides prospects and considerations for QD-based photoelectrochemical sensor systems in terms of their sensitivity, speed, and portability for biomedical applications.

Nanotechnology‐based electrochemical biosensors for monitoring breast cancer biomarkers

Breast cancer is categorized as the most widespread cancer type among women globally. On-time diagnosis can decrease the mortality rate by making the right decision in the therapy procedure. These features lead to a reduction in medication time and socioeconomic burden. The current review article provides a comprehensive assessment for breast cancer diagnosis using nanomaterials and related technologies. Growing use of the nano/biotechnology domain in terms of electrochemical nanobiosensor designing was discussed in detail. In this regard, recent advances in nanomaterial applied for amplified biosensing methodologies were assessed for breast cancer diagnosis by focusing on the advantages and disadvantages of these approaches. We also monitored designing methods, advantages, and the necessity of suitable (nano) materials from a statistical standpoint. The main objective of this review is to classify the applicable biosensors based on breast cancer biomarkers. With numerous nano-sized platforms published for breast cancer diagnosis, this review tried to collect the most suitable methodologies for detecting biomarkers and certain breast cancer cell types.

One-step homogeneous micro-orifice resistance immunoassay for detection of chlorpyrifos in orange samples

In this work, a one-step homogeneous micro-orifice resistance immunoassay has been proposed for chlorpyrifos detection by integrating functionalized polystyrene (PS) microsphere probes with particle counting technology. The particle counter is highly sensitive and accurate for detecting the state of PS microspheres, where the particles of different states exhibit significant differences in resistance. The state of the functionalized PS microspheres is altered from dispersed to aggregated during the antigen-antibody recognition. Based on the degree of aggregation of the functionalized PS microsphere probes, chlorpyrifos can be quantitatively detected through the competitive immune response between PS antibodies and PS complete antigens. This one-step homogeneous micro-orifice resistance immunoassay simplified the procedures and greatly increased the sensitivity of detection, which has been successfully applied to detect chlorpyrifos in orange samples within 0.5 h, with the detection limit of 0.058 ng/mL.

Ammonium Ionic Liquid-Functionalized Phenothiazine as a New Redox Mediator for High Chemical Stability on the Anode Surface in Lithium-Air Batteries

The application of redox mediators (RMs) as soluble catalysts can address the problem of insufficient contact between conventional solid catalysts for lithium-air batteries (LABs). However, oxidized RM molecules migrate to the lithium anode and react with lithium, which results in the accumulation of surface corrosion products that weaken the redox activity of the RM. This paper presents a new combination of phenothiazine (PTZ) as an RM and an ammonium-based ionic liquid (IL) source as a protective agent to prevent the side reactions with lithium and to enhance the electrochemical performance of LABs. IL-functionalized PTZ (IL-PTZ) was successfully synthesized through N-alkylation, quaternization, and anion-exchange reactions. IL-PTZ improved the chemical stability of the RM molecules on the lithium surface as well as the electrochemical performance. A microstructural analysis revealed that the IL group in the IL-PTZ molecules facilitated smooth lithium stripping/plating by blocking the side reactions between the RM and lithium. Compared with the LAB with the PTZ electrolyte, that with the IL-PTZ electrolyte exhibited a significantly higher discharge capacity (2500 mA h/g vs 1500 mA h/g) and a cycle life that was 2 times longer. The IL-PTZ molecule was demonstrated to exhibit great potential as a novel soluble catalyst for application in high-performance LABs.

Electrochemical detection of methyl-paraoxon based on bifunctional cerium oxide nanozyme with catalytic activity and signal amplification effect

A new electrochemical sensor for organophosphate pesticide (methyl-paraoxon) detection based on bifunctional cerium oxide (CeO₂) nanozyme is here reported for the first time. Methyl-paraoxon was degraded into p-nitrophenol by using CeO₂ with phosphatase mimicking activity. The CeO₂ nanozyme-modified electrode was then synthesized to detect p-nitrophenol. Cyclic voltammetry was applied to investigate the electrochemical behavior of the modified electrode, which indicates that the signal enhancement effect may attribute to the coating of CeO₂ nanozyme. The current research also studied and discussed the main parameters affecting the analytical signal, including accumulation potential, accumulation time, and pH. Under the optimum conditions, the present method provided a wider linear range from 0.1 to 100 μmol/L for methyl-paraoxon with a detection limit of 0.06 μmol/L. To validate the proof of concept, the electrochemical sensor was then successfully applied for the determination of methyl-paraoxon in three herb samples, i.e., Coix lacryma-jobi, Adenophora stricta and Semen nelumbinis. Our findings may provide new insights into the application of bifunctional nanozyme in electrochemical detection of organophosphorus pesticide.

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A new electrochemical method for methyl-paraoxon detection by using bifunctional nanozyme was presented.

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The cerium oxide nanozyme modified glassy carbon electrode was prepared to improve the sensitivity.

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The developed method has been successfully applied in three herbal plant samples.

Construction of a Polarity-Switchable Photoelectrochemical Biosensor for Ultrasensitive Detection of miRNA-141

As an early-stage tumor biomarker, microRNA (miRNA) has clinical application potential and its sensitive and accurate detection is significant for early tumor diagnosis. In this study, a photoelectrochemical (PEC) biosensing platform was fabricated for ultrasensitive miRNA-141 detection, which is based on a photocurrent polarity-switchable system using CdS quantum dots (QDs) in the presence of a 5,10,15,20-tetrakis (4-aminophenyl)-21H,23H-porphine (Tph-2H)-coated glassy carbon electrode (GCE). As an excellent photoactive material, Tph-2H has a narrow band gap that effectively gathers photoelectrons under visible light irradiation and improves the transfer ability of photogenerated electrons. Further, the detection sensitivity of miRNA-141 could be significantly improved by combining an enzyme-assisted recycle amplification reaction and a magnetic bead-based separation strategy. The proposed photocurrent polarity-switchable PEC biosensor could efficiently eliminate the false-positive or false-negative signals and achieve a wide linear response range from 1 fM to 1 nM with a low detection limit of 0.33 fM for miRNA-141, providing a potentially alternative solution for detecting other biomarkers in bioanalysis and clinical diagnosis.

Photoelectrochemical Assay Based on SnO2/BiOBr p-n Heterojunction for Ultrasensitive DNA Detection

Herein, a photoelectrochemical (PEC) assay was designed for a highly sensitive DNA determination relying upon the SnO₂/BiOBr p-n heterojunction as a photoactive material and SiO₂ as a signal quencher. Compared with most traditional heterojunctions, the SnO₂/BiOBr p-n heterostructure not only lessened the recombination of the photogenerated electron-hole pairs but also promoted the light-harvesting in the ultraviolet-visible (UV-vis) region, leading to further enhanced photoelectric conversion efficiency and photocurrent, which demonstrated 12.1-fold and 6.4-fold increments versus those of pure SnO₂ and BiOBr, respectively. Additionally, the limited quantity of target DNA (a fragment of p53 gene) could be transformed into abundant output DNA-SiO₂ by employing the Nt·BstNBI enzyme-assisted signal amplification procedure, leading to a highly improved detection sensitivity of the biosensor. Then, output DNA-SiO₂ hybridized with the capture DNA anchored on the modified electrode surface, remarkably diminishing the PEC signal and thus achieving sensitive DNA determination. The elaborated PEC biosensor demonstrated outstanding performance within the linear range between 0.5 fM and 5 nM and a low limit of detection down to 0.18 fM, paving a new way for fabricating heterojunction with exceptional photoactive performance and demonstrating the enormous potential for detecting multitudinous biomarkers in bioanalysis and clinical therapy.

A photoelectrochemical sensor based on an acetylcholinesterase-CdS/ZnO-modified extended-gate field-effect transistor for glyphosate detection

A new photoelectrochemical enzyme biosensor based on an extended-gate field-effect transistor (EGFET) was constructed for the highly sensitive detection of glyphosate based on the inhibition of acetylcholinesterase (AChE) activity by glyphosate. First, a two-step hydrothermal method was used to introduce ZnO and CdS onto an activated indium tin oxide (ITO) electrode to prepare a CdS/ZnO/ITO electrode. Then, AChE was immobilized on CdS/ZnO/ITO with chitosan to obtain an AChE/CdS/ZnO EGFET sensor. Under optimal experimental conditions, the logarithmic value of glyphosate in the range of 1.0 × 10-15-1.0 × 10-11 mol L-1 exhibited a good linear relationship with the photo-drain current response. The detection limit was 3.8 × 10-16 mol L-1 (signal-to-noise ratio = 3). The results show that the AChE/CdS/ZnO EGFET sensor has extremely high sensitivity and good selectivity. Moreover, the sensor was used for the determination of glyphosate in vegetables, demonstrating its application for the real-time detection of samples.

Visible light mediated self-powered sensing based on target induced recombination of photogenerated carriers

Self-powered sensing platforms have received widespread attention in areas such as portable, wearable and point-of-care devices. Here we reported visible light mediated self-powered electrochemical sensing based on target induced recombination of photogenerated carriers, which has highly sensitive to detect copper ions concentration. We utilized the recombination of photogenerated carriers mechanism to design visible light-responsive Fe₂O₃-CdS n-n heterojunction as photoanode material, which greatly improved the problem of output energy in photocatalytic self-powered sensors. Expectedly, our proposed visible light mediated self-powered electrochemical system has high separation efficiency of photogenerated carriers, which is 8.4 times that in presence of Cu²⁺. Furthermore, this self-powered electrochemical sensing platform used Cu²⁺ induced recombination of photogenerated carriers, showed a clear linear relationship from 1 nM to 5000 nM with an acceptable detection limit of 0.4 nM. This self-powered electrochemical sensing platform with excellent selectivity, accredited reproducibility and believable stability exhibited promising prospects in developing portable sensing devices and detection chip for real-time and rapid monitoring of Cu²⁺.

Simultaneous and ultrasensitive detection of three pesticides using a surface-enhanced Raman scattering-based lateral flow assay test strip

Chlorothalonil (CHL), imidacloprid (IMI) and oxyfluorfen (OXY) are commonly used in combination to increase crop yield. However, these three pesticides are toxic to aquatic organisms and do not easily degrade. In this study, a surface-enhanced Raman scattering-based lateral flow assay (SERS-LFA) test strip was prepared by combining antibodies with SERS nanotags, and then competitive immune binding was used to detect the three pesticides simultaneously. Moreover, the two-way binding effect of ssDNA-streptavidin bound to Ag^4-NTP@AuNPs and Ag^4-NTP@AuNPs with antibodies was used to further amplify the detection signal. Under the optimal conditions, the SERS-LFA test strips exhibited high sensitivity, a low detection limit, short detection time, high specificity and low cost. Furthermore, the detection range was within the values prescribed by international detection standards. By measuring the intensity of the SERS signal on the test line of the paper strip, accurate quantitative analysis was achieved. The practical application of the proposed system was demonstrated by simultaneous detection of CHL, IMI and OXY in environmental and food samples with satisfactory results.

An OliGreen-responsive fluorescence sensor for sensitive detection of organophosphorus pesticide based on its specific selectivity towards T-Hg2+-T DNA structure

In this paper, it was found that OliGreen emitted much stronger fluorescence in rigid T-Hg²⁺-T DNA structure than that in the presence of poly T. Thus, an OliGreen-responsive label-free fluorescent sensor was proposed for sensitive detection of organophosphorus pesticides (OPs) by constructing T-Hg²⁺-T DNA structure. OliGreen emits strong fluorescence in T-Hg²⁺-T structures. The rigid DNA structure of T-Hg²⁺-T is prone to be destroyed by thiocholine (TCh) that hydrolyzed by acetylcholinesterase (AChE) because of the high affinity of TCh with Hg²⁺. As a result, T-Hg²⁺-T DNA structure broke down and the fluorescence intensity of OliGreen decreased greatly. With the inhibition of AChE by OPs, fluorescence intensity of OliGreen remained strong because of the rigid T-Hg²⁺-T DNA structure. Thus, a "turn-on" fluorescent sensor which avoids synthesis of nanomaterials and complex label procedures is proposed based on the fluorescence intensity of OliGreen. DDVP were detected with a wide linear range from 0.005 to 25.0 ng/mL and the detection limit was 2.9 pg/mL, which is more sensitive than previously reported methods.

Dual-Mode Aptasensor Assembled by a WO3/Fe2O3 Heterojunction for Paper-Based Colorimetric Prediction/Photoelectrochemical Multicomponent Analysis

The programed bimodal photoelectrochemical (PEC)-sensing platform based on DNA structural switching induced by targets binding to aptamers was innovatively designed for the simultaneous detection of mucin 1 (MUC1) and microRNA 21 (miRNA-21). To promote excellent current intensity as well as enhance the sensitivity of aptasensors, the evenly distributed WO₃/Fe₂O₃ heterojunction was prepared as a transducer material, notably reducing the background signal response and extending the absorption of light. The multifunctional paper-based biocathode was assembled to provide a visual colorimetric assay. When introducing the integrated signal probe (ISP) composed of signal probe 1 (sP1) and signal probe 2 (sP2) on paper-based working units modified with gold nanoparticles (AuNPs), recognition sites of two targets were formed. In the presence of MUC1 protein, both sP1 and the target on the working unit were released into the corresponding colorimetric unit because of the DNA specific recognition. The horseradish peroxidase-streptavidin (HRP-SA) carried by free sP1 could oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to turn a blue-colored oxidized TMB (oxTMB) in the presence of hydrogen peroxide (H₂O₂), which ultimately gained a higher photocurrent signal. Furthermore, miRNA-21 was modified on another working unit by binding with sP2, leading to changes in the current signal and thus enabling real-time detection of analytes with the assistance of a digital multimeter. The PEC aptasensor offered a wide dynamic range of 10 fg·mL^-1-100 ng mL^-1 for MUC1 and 0.1 pM-10 nM for miRNA-21, with a low detection limit of 3.4 fg·mL^-1 and 36 fM, respectively. It laid the foundation for synchronous detection of multiple analytes and initiated a new way for the enhancement in modern next-generation disease diagnosis.

Functional polymers in photoelectrochemical biosensing

Photoelectrochemical (PEC) analysis is a detection technique that has gained a wide attention in sensing applications. PEC presents the advantages of high sensitivity, low background signal, simple equipment and easy miniaturization. In PEC detection, light is used as an excitation source while current or voltage is measured as the output detection signal. The ability to couple the PEC process with specific bioreceptors gives PEC biosensing a unique advantage of being both selective and sensitive. The growing interest in PEC bioanalysis has resulted in essential progress in its analytical performance and biodetection applications. Functional polymers have different applications in the development of novel PEC biosensing platforms. Recently, the interest in polymer-based photoactive materials has emerged as they are efficient and less toxic alternatives to certain kinds of inorganic semiconductors and sensitizers. Moreover, molecularly imprinted polymers are a class of synthetic bioreceptors that are increasingly used in PEC bioanalytics. In this review, we will provide an overview on functional polymer-based PEC biosensing approaches. Novel classes of polymers as photoactive materials are reviewed and selected applications are described. Furthermore, molecularly imprinted polymers in the development of smart and sensitive PEC bioanalytical strategies are discussed.

An enzyme inhibition-based lab-in-a-syringe device for point-of-need determination of pesticides

An enzyme inhibition-based lab-in-a-syringe (EI-LIS) device was developed by integrating a 1-naphthol-linked bi-enzymatic reaction (sensor core) into the LIS (sensor device) for point-of-need monitoring of pesticide residues.