PEC-SERS Dual-Mode Detection of Foodborne Pathogens Based on Binding-Induced DNA Walker and C3N4/MXene-Au NPs Accelerator

Photoelectrochemical and fluorescent dual-mode sensitive detection of circulating tumor cells based on aptamer DNA-linked CdTe QDs/Bi2MoO6/CdS "double Z-scheme" system

Herein, a novel dual-mode biosensor integrating photoelectrochemical (PEC) and fluorescence (FL) sensing detection was developed for circulating tumor cells (CTCs) based on aptamer DNA-linked CdTe QDs (Apt-CdTe QDs)/Bi2MoO6/CdS "dual Z-scheme" sensing system. Apt-CdTe QDs were assembled on FTO/CdS/Bi2MoO6/cDNA electrode through hybridization with cDNA, resulting in the formation of a double Z-scheme CdS/Bi2MoO6/CdTe heterostructure that significantly enhanced the separation of photo-generated charge carriers, thereby improving photocatalytic efficiency. Upon the presence of MCF-7 cells, Apt-QDs were captured and subsequently released from the captured electrode, leading to a decrease in photocurrent and an increase in fluorescence intensity, thus enabling effective PEC-FL dual-mode detection. The detection of CTCs exhibited a linear relationship within the concentration range from 50 to 100000 cells mL-1 with limit of detection of 1 cell mL-1 in both PEC and FL modes. This approach effectively corrected systematic errors, improved detection accuracy and sensitivity, and held great potential in the clinical detection of CTCs.

SERS and ECL dual-mode sensing of bacterial lipopolysaccharide based on bifunctional DNA strands mediated transformation from Au@Ag nanocubes to silver nanoclusters

Bacterial contamination is a very serious health and environmental problem, with the main source of toxicity being lipopolysaccharides in the cell walls of Gram-negative bacteria. Therefore, the development of effective analytical methods is crucial for the detection of lipopolysaccharide content. This work facilitates the efficient generation of precisely adjustable dual-mode signals for LPS detection in surface-enhanced Raman spectroscopy (SERS) and electrochemiluminescence (ECL) by inducing anisotropic morphological evolution of Au@Ag nanocubes (Au@AgNCs) through poly-cytosine (poly-C) DNA. In the presence of LPS, the released probe triggers rolling circle amplification (RCA) and generates cyclic poly-C DNA, which subsequently induces the etching of Ag composites on Au@AgNCs. This etching process leads to changes in both the morphology and composition of Au@AgNCs composite materials, resulting in a decrease in SERS signals. The poly-C DNA was subsequently adsorbed with Ag+ and then reduced to silver nanoclusters (AgNC) by NaBH4, serving as an ECL signal source. Under optimal experimental conditions, both SERS and ECL demonstrated linear ranges spanning from 1 fg/mL to 1 ng/mL, with detection limits of 0.29 fg/mL and 0.14 fg/mL, respectively. Moreover, the SERS-ECL dual-mode sensor facilitates the accurate discrimination of Gram-negative bacteria in diverse real samples. It demonstrates promising applications in the areas of food safety, water quality monitoring, and clinical bacterial detection.

MXenes in microbiology and virology: from pathogen detection to antimicrobial applications

MXenes, a rapidly emerging class of two-dimensional materials, have demonstrated exceptional versatility and functionality across various domains, including microbiology and virology. Recent advancements in MXene synthesis techniques, encompassing both top-down and bottom-up approaches, have expanded their potential applications in pathogen detection, antimicrobial treatments, and biomedical platforms. This review highlights the unique physicochemical properties of MXenes, including their large surface area, tunable surface chemistry, and high biocompatibility, which contribute to their antimicrobial efficacy against bacteria, fungi, and viruses, such as SARS-CoV-2. The antibacterial mechanisms of MXenes, including membrane disruption, reactive oxygen species (ROS) generation, and photothermal inactivation, are discussed alongside hybridization strategies that enhance their bioactivity. Additionally, the challenges and future prospects of MXenes in developing advanced antimicrobial coatings, diagnostic tools, and therapeutic systems are outlined. By addressing current limitations and exploring innovative solutions, this study underscores the transformative potential of MXenes in microbiology, virology, and biomedical applications.

Organic Molecules as a Bridge Connecting Photoelectrochemistry and Fluorescence for Dual-Signal Assay

We report a strategy based on pyridyl-anchored organic small-molecule fluorescent probes to develop a dual-signal sensing platform. The strategy accomplishes an intelligent integration of fluorescence analysis with photoelectrochemical (PEC) sensing, thereby enabling rapid and precise detection of hypochlorite. In this work, the natural dye chromone was selected as the fluorophore for generating fluorescent signals. Meanwhile, by using phenothiazine (PTZ) as the specific recognition group and pyridine as the anchoring moiety, we designed and synthesized a novel organic small-molecule fluorescent probe. The obtained probe was used as a photosensitive material anchored to the TiO2 surface via N → Ti bonds, to form an FTO/TiO2/FPTZ-1 heterostructure-based dual-signal sensing platform for the detection of hypochlorite. This sensing platform has the characteristics of high specificity, sensitivity, and ease of preparation, enabling rapid qualitative fluorescence readout and quantitative photoelectrochemical readout of hypochlorite, with a limit of detection of 0.288 μM for fluorescence and 1.37 nM for PEC.

CRISPR/Cas12a-powered nanoconfined biosensing platform with hybrid chain reaction cascading guanine nanowire amplification for ultrasensitive dual-mode detection of lipopolysaccharide

Traditional endotoxin detection methods face challenges in sensitivity, interference resistance, and reliability. This study develops a CRISPR/Cas12a-powered nanoconfined biosensing system that integrates mesoporous nanoengineering with a hybrid chain reaction (HCR) cascading guanine nanowire (G-wire) dual amplification strategy for ultrasensitive dual-mode detection of lipopolysaccharide (LPS). By leveraging a vertically ordered mesoporous silica membrane (VMSM) as a molecular sieve and CRISPR trans-cleavage activity modulator, the system achieves precise regulation of Ru(bpy)32+ adsorption via LPS-suppressed HCR assembly. This architecture enables physical confinement-mediated electrochemiluminescence (ECL) and fluorescence (FL) signal transduction, with dual-mode outputs providing mutual validation for enhanced reliability. The biosensor exhibits superior sensitivity with detection limits of 3.4 pg mL-1 for ECL and 1.4 pg mL-1 for FL, while also offering a broad dynamic range (0.005-100 ng mL-1), significantly outperforming conventional LPS assays. The CRISPR-triggered HCR cascading G-wire dual amplification synergizes with nanoconfinement of VMSM to ensure robust anti-interference performance in complex matrices, validated by recovery rates of 97.8-102.5% in real samples. By integrating CRISPR programmability with nanoengineered signal amplification, this work establishes a transformative paradigm for portable, high-precision endotoxin detection in clinical diagnostics, industrial monitoring, and environmental safety applications.

Advances in Functional Nucleic Acid SERS Sensing Strategies

Functional nucleic acids constitute a distinct category of nucleic acids that diverge from conventional nucleic acid amplification methodologies. They are capable of forming intricate hybrid structures through Hoogsteen and reverse Hoogsteen hydrogen bonding interactions between double-stranded and single-stranded DNA, thereby broadening the spectrum of DNA interactions. In recent years, functional DNA/RNA-based surface-enhanced Raman spectroscopy (SERS) has emerged as a potent platform capable of ultrasensitive and multiplexed detection of a variety of analytes of interest. This review aims to elucidate the operational principles of several functional nucleic acids in SERS detection, including DNAzymes, G-quadruplexes, aptamers, CRISPR, origami etc., alongside the design methodologies and practical applications of functional DNA/RNA-based SERS sensing. Initially, an overview is summarized encompassing the structural attributes and SERS sensing mechanisms inherent to diverse functional DNA/RNA. Following this, various innovative strategies for constructing functional nucleic acid-based SERS sensors are illustrated in detail, aimed at improving the present detection capabilities. A comprehensive summing up is then conducted on the applications of these sensors in crucial fields, such as disease diagnosis, environmental monitoring, and food safety detection, with a particular focus on SERS sensitivity, specificity, and analytical versatility. Finally, conclusive remarks are offered along with an exploration of the existing challenges and prospective avenues for future research in this developed field.

Signal-off based dual-mode sensing platform for ultrasensitive detection of antibiotics in food samples

Development of efficient and accurate detection methods for antibiotics is crucial for ensuring food safety and safeguarding human health. In this study, a dual-mode sensing platform was constructed by integrating photoelectrochemical (PEC) and surface-enhanced Raman scattering (SERS) techniques for the sensitive detection of kanamycin using an aptamer signal conversion strategy which was based on the C3N4/MXene-gold nanoparticles heterojunction. The sensitive dual-mode sensing platform enabled detection of kanamycin, with linear response ranges of 10-3 to 105 nM for PEC with a detection limit (LOD) of 0.53 pM, and 10-2 to 104 nM for SERS with a LOD of 4.8 pM. Notably, this platform exhibited excellent performance for kanamycin assays in raw milk. Furthermore, combined with various aptamer-targets, it can be easily broadened to detect more low concentration target substances in other complex matrix, showcasing its vast potential for diverse applications.

Photocatalytic Organic Semiconductor-Bacteria Imprinted Polymers for Highly Selective Determination of Staphylococcus aureus at the Single-Cell Level

This work utilized a combination of photocatalytic organic semiconductors and bacteria to create a photocatalytic organic semiconductor-bacterial biomixture system based on a bacteria imprinted polymers (OBBIPs-PEC) sensor, for the detection of S. aureus with high sensitivity in "turn-on" mode at the single-cell level. This outstanding sensor arises from an integration of two different types of semiconductor materials to form heterojunctions. As well this sensor involves combining a semiconductor material with cationic side chains and an electron transport chain within a natural cellular environment, in which the cationic side chain of poly(fluorene-co-phenylene) organic semiconductor at 2-(4-mesyl-2-nitrobenzoyl)-1,3-cyclohexanedione (PFP-OC@MNC) demonstrated the ability to penetrate the cell membrane of S. aureus and interact with specific binding sites through electrostatic interactions. As the cavities in the BIPs were occupied by S. aureus, during light irradiation, the electrons stimulated by the photoexcitation process in the manufactured PFP-OC@MNC semiconductors were successfully transmitted to S. aureus, where these electrons played a role in the regeneration of NADH and FADH2, and then the presence of S. aureus acted as a proficient electron acceptor for photoexcited electrons; thereby the PEC response of the OBBIPs-PEC sensor was significantly enhanced. Of note, it exhibited high selectivity for S. aureus over other bacteria and maintained excellent performance in complex matrices, distinguishing S. aureus with concentrations as low as 10 CFU/mL. This work dramatically reduces the influence of interference factors in the traditional mode and offers a powerful way for microorganism detection in food and environmental fields.

Advanced surface-enhanced raman scattering nanoprobes for precise detection of Nitroreductase in Hypoxic tumor cells: Improving Cancer diagnosis

Nitroreductase (NTR) plays a critical role in the oxygen-deficient environment of anoxic tumor cells, and its identification is crucial for the diagnosis and treatment of cancer. This research introduces an innovative Surface Enhanced Raman Scattering (SERS) probe, created by attaching p-nitrothiophenol (p-NTP) to gold nanoparticles (Au NPs). This probe leverages the specific enzymatic reaction of NTR in hypoxic status, utilizing decreased NADH. The enzymatic activity of NTR transforms nitroaromatic compounds into aromatic amines, which is then reflected as a measurable shift in the SERS signal of the probe. This novel approach allows for the accurate quantification of NTR, with the sensitivity reaching a detection threshold of less than 0.02 μg/mL. The probe's non-toxic nature and superior biocompatibility facilitate its use for direct SERS investigations in A549 cells under reduced oxygen levels. We also applied this method to xenograft model. The results demonstrate a marked increase in NTR levels in tumor cells and tumor tissues in hypoxic conditions, highlighting the significance of this nanoprobe in enhancing cancer diagnostics, helping medical doctors making treatment decisions more swiftly and effectively.

Photoexcited CuO/TiO2 Heterojunction for Photoelectrochemical Sensors for Nonenzymatic Glucose Detection

Photoelectrochemical sensors have been studied for glucose detection because of their ability to minimize background noise and unwanted reactions. Titanium dioxide (TiO2), a highly efficient material in converting light into electricity, cannot utilize visible light. In this regard, we developed a nonenzymatic glucose sensor by using a simple one-step electrospinning technique to combine cupric oxide with TiO2 to create a heterojunction. The prepared nanofibers exhibit an extremely high aspect ratio and have a dense structure. These characteristics enhance the quantity of electron-hole pairs generated by light and the speed at which electrons are transferred. They also reduce the distance that charges need to travel and offer reactive sites for the catalytic oxidation of glucose. The sensor has a direct and proportional reaction within glucose concentration ranging from 30 μM to 2 mM under sunlight conditions. It achieves a detection limit of 9.9 μM with a signal-to-noise ratio of 3. The sensors also exhibit excellent stability, reproducibility, and selectivity. This study provides insights for development of photoelectrochemical sensors to detect glucose.

Advanced Dual-Mode Microfluidic Sensing Platform Based on Amphiphilic Polymer-Capped Perovskite Nanozymes Induced Photoelectrochemical Signal Amplification and Fluorescence Emission

A novel dual-mode microfluidic sensing platform integrating photoelectrochemical (PEC) and fluorescence (FL) sensors was developed for the sensitive monitoring of heart fatty acid binding protein (h-FABP). First, BiVO4/AgInS2 (BVAIS) composites with excellent photoelectric activity were synthesized as sensing matrices. The BVAIS heterojunction with a well-matched internal energy level structure provided a stable photocurrent. Second, an innovative signal amplification strategy based on octylamine-modified poly(acrylic acid) (OPA)-capped CsPbBr3 (OPCB) nanocrystals (NCs) with excellent catalytic activity and fluorescence property was proposed. On the OPCB nanozyme possessing ascorbate oxidase-like catalytic activity could catalyze the oxidation of ascorbic acid, which achieved quenching of the photocurrent signals by competitively consuming the electron donor. On the other hand, the OPCB NCs that overcame the water stability defect processed good luminescence performance and were able to produce obvious FL signals. Mutually verified dual-response signals effectively enhance the precision of test outcomes and avoid false-positive or false-negative results. Finally, the constructed microfluidic sensing platform realized sensitive detection of h-FABP in the linear range of 0.0001-150 ng/mL (PEC mode) and 0.001-150 ng/mL (FL mode), with detection limits of 36 fg/mL and 0.32 pg/mL, respectively. The present work provided a new perspective for designing an efficient dual-mode sensing strategy to achieve sensitive detection of disease markers.

Operando Photoelectrochemical Surface-Enhanced Raman Spectroscopy: Interfacial Mechanistic Insights and Simultaneous Detection of Patulin

Comprehending the biosensing mechanism of the biosensor interface is crucial for sensor development, yet accurately reflecting interfacial interactions within actual detection environments remains an unsolved challenge. An operando photoelectrochemical surface-enhanced Raman spectroscopy (PEC-SERS) biosensing platform was developed, capable of simultaneously capturing photocurrent and SERS signals, allowing operando characterization of the interfacial biosensing behavior. Porphyrin-based MOFs (Zr-MOF) served as bifunctional nanotags, providing a photocurrent and stable Raman signal output under 532 nm laser irradiation. Aptamer was used to bridge the Zr-MOF and the silver-encased gold nanodumbbells (AuNDs@AgNPs). The simultaneous in situ acquisition of target-induced PEC and SERS signal responses facilitated the correlation of electron transfer information from the photocurrent with the distance information from the SERS signal. It revealed the biosensing mechanism in which target-induced aptamer conformational bending drove the Zr-MOF to approach the electrode. However, the increase in charge transfer observed through conventional electrochemical methods contradicts the conclusions drawn from the operando PEC-SERS analysis. Comprehensive analysis indicated that redox probes introduced during the non-in-situ measurement process became adsorbed within the MOF pores, potentially affecting the judgment of the biosensing mechanism. In addition, the operando PEC-SERS biosensor simultaneously obtained two independent signals, providing self-verification to improve the accuracy and reliability of patulin detection. The linear ranges were 1 pg mL-1-10 ng mL-1 for the PEC method and 1 pg mL-1-100 ng mL-1 for the SERS method, respectively. This work provides a powerful tool for determining the interface characteristics of biosensors.

Energy-Transfer-Based Dual-Mode PEC-ECL Biosensor for Acetamiprid Analysis Sensitized by Two-Step DNA Circuit Amplification

Sensitive and accurate determination of acetamiprid is highly desirable for guaranteeing food safety. In this Letter, an energy-transfer-based dual-mode biosensor was developed using zinc-based metal-organic frameworks (Zn-MOFs) acting as both photoelectrochemical (PEC) and electrochemiluminescent (ECL) donors and Pt@Cu2O cubic nanocrystals (CNs) as the energy acceptor for detecting acetamiprid. By integration of aptamer recognition with two-step DNA circuit amplification (entropy-driven DNA cycle and DNA walker), the detection of acetamiprid was converted into the assay of abundant intermediate DNA strands. With the help of nicking endonuclease, a large number of single-stranded DNAs was generated on the surface of Zn-MOFs, which were used as multifunctional PEC and ECL substrates. Through competitive hybridization, Pt@Cu2O CNs as broad-spectrum quenchers were introduced, thereby enabling changes in the PEC and ECL responses for acetamiprid quantitation. The experimental results proved that the combination of energy transfer, two-step DNA circuit amplification, and dual-mode sensing strategy achieved the sensitive and accurate analysis of acetamiprid, with low detection limits of 20.2 fM (PEC mode) and 17.5 fM (ECL mode) within a wide range from 0 to 1 × 10-9 M. The excellent specificity, reproducibility, and practicality confirmed the potential application of the biosensor for pesticide-related food safety.

Protein-Induced DNA Dumbbell Amplification (PINDA) and its applications to food hazards detection

Quantification of trace amounts of proteins is technically challenging because proteins cannot be directly amplified like nucleic acids. To improve the analytical sensitivity and to complement conventional protein analysis methods, we developed a highly sensitive and homogeneous detection strategy called Protein-Induced DNA Dumbbell Amplification (PINDA). PINDA combines protein recognition with exponential nucleic acid amplification by using protein binding probes made of DNA strands conjugated to protein affinity ligands. When a pair of probes bind to the same target protein, complementary nucleic acid sequences that are conjugated to each probe are brought into close proximity. The increased local concentration of the probes results in the formation of a stable dumbbell structure of the nucleic acids. The DNA dumbbell is readily amplifiable exponentially using techniques such as loop-mediated isothermal amplification. The PINDA assay eliminates the need for washing or separation steps, and is suitable for on-site applications. Detection of the model protein, thrombin, has a linear range of 10 fM-100 pM and detection limit of 10 fM. The PINDA technique is successfully applied to the analysis of dairy samples for the detection of β-lactoglobulin, a common food allergen, and Salmonella enteritidis, a foodborne pathogenic bacterium. The PINDA assay can be easily modified to detect other targets by changing the affinity ligands used to bind to the specific targets.

Highly sensitive SERS nanoplatform based on aptamer and vancomycin for detection of S. aureus and its clinical application

Staphylococcus aureus (S. aureus) is the most common pathogen in human purulent infections, which can cause local purulent infections, as well as pneumonia, pseudomembranous enteritis, pericarditis, and even systemic infections. The conventional methods including bacteria colony counting, polymerase chain reaction and enzyme-linked immunosorbent assay can't fully meet the requirement of highly sensitive detection of S. aureus due to their own disadvantages. Therefore, it's an urgent need to develop new platform to detect S. aureus in the early infection stage. In this study, a new surface-enhanced Raman scattering (SERS)-based nanoplatform based on dual-recognition of aptamer (Apt) and vancomycin (Van) was developed for the highly sensitive detection of S. aureus. The SERS nanoplatform consisted of two functional parts: aptamer-conjugated Fe3O4 magnetic nanoparticles (Fe3O4-Apt MNPs) for bacteria enrichment and vancomycin modified-Au nanoparticles (Van-Au NPs) as the SERS probes for S. aureus quantitative detection. Upon the target bacteria enrichment, the SERS signals of the supernatant after magnetic separation could be obtained and analyzed under different concentrations of S. aureus. The limit of detection of the proposed assay was found to be 3.27 CFU/mL. We believe that the proposed SERS-based nanoplatform has great potential as a powerful tool in the early detection of specific bacteria.

Rapid Dynamic Surface-Enhanced Raman Spectroscopy Detection of Amoxicillin-Mediated Morphological Changes in a Pathogen for Diagnosis of Clinical Urine Samples

The swift and stable detection of pathogens in urine samples holds significant implications for the immediate clinical diagnosis and treatment of urinary tract infections (UTIs). In this study, we propose a detection strategy utilizing a hybrid substrate composed of graphene oxide (GO) and silver nanoparticles (Ag NPs) for the detection of pathogens subjected to amoxicillin-mediated (amo-mediated) treatment. This strategy employs dynamic surface-enhanced Raman spectroscopy (D-SERS) for stable and rapid detection, capturing signal variations induced by amo-mediated changes in pathogen morphology. During the 5 min D-SERS detection time window, stable SERS signals were detected for three types of pathogens and four types of pathogens were successfully distinguished using principal component analysis (PCA). In comparison to conventional nanosubstrates, the GO/Ag NP hybrid substrate exhibits outstanding stability and enhancement effects. This approach enables the dual detection of the pathogen cell structure and metabolites, facilitating specific identification of pathogens in the urinary tract, with a detection limit for Escherichia coli reaching 1 × 104 colony-forming units (CFU)/mL, meeting the clinical microbiology laboratory diagnostic standards for UTIs (105 CFU/mL). Testing of 188 clinically collected urine samples using this strategy yielded a sensitivity (SENS) of 86.4% and a specificity (SPC) of 89.7%. This introduces a novel method for diagnosing UTIs, offering broad applications in the field of clinical pathogen detection.

Recent Progress in Nanomaterial-Based Surface-Enhanced Raman Spectroscopy for Food Safety Detection

Food safety has recently become a widespread concern among consumers. Surface-enhanced Raman scattering (SERS) is a rapidly developing novel spectroscopic analysis technique with high sensitivity, an ability to provide molecular fingerprint spectra, and resistance to photobleaching, offering broad application prospects in rapid trace detection. With the interdisciplinary development of nanomaterials and biotechnology, the detection performance of SERS biosensors has improved significantly. This review describes the advantages of nanomaterial-based SERS detection technology and SERS's latest applications in the detection of biological and chemical contaminants, the identification of foodborne pathogens, the authentication and quality control of food, and the safety assessment of food packaging materials. Finally, the challenges and prospects of constructing and applying nanomaterial-based SERS sensing platforms in the field of food safety detection are discussed with the aim of early detection and ultimate control of foodborne diseases.

Nanopore-based sensors for DNA sequencing: a review

Nanopore sensors, owing to their distinctive structural properties, can be used to detect biomolecular translocation events. These sensors operate by monitoring variations in electric current amplitude and duration, thereby enabling the calibration and distinction of various biomolecules. As a result, nanopores emerge as a potentially powerful tool in the field of deoxyribonucleic acid (DNA) sequencing. However, the interplay between testing bandwidth and noise often leads to the loss of part of the critical translocation signals, presenting a substantial challenge for the precise measurement of biomolecules. In this context, innovative detection mechanisms have been developed, including optical detection, tunneling current detection, and nanopore field-effect transistor (FET) detection. These novel detection methods are based on but beyond traditional nanopore techniques and each of them has unique advantages. Notably, nanopore FET sensors stand out for their high signal-to-noise ratio (SNR) and high bandwidth measurement capabilities, overcoming the limitations typically associated with traditional solid-state nanopore (SSN) technologies and thus paving the way for new avenues to biomolecule detection. This review begins by elucidating the fundamental detection principles, development history, applications, and fabrication methods for traditional SSNs. It then introduces three novel detection mechanisms, with a particular emphasis on nanopore FET detection. Finally, a comprehensive analysis of the advantages and challenges associated with both SSNs and nanopore FET sensors is performed, and then insights into the future development trajectories for nanopore FET sensors in DNA sequencing are provided. This review has two main purposes: firstly, to provide researchers with a preliminary understanding of advancements in the nanopore field, and secondly, to offer a comprehensive analysis of the fabrication techniques, transverse current detection principles, challenges, and future development trends in the field of nanopore FET sensors. This comprehensive analysis aims to help give researchers in-depth insights into cutting-edge advancements in the field of nanopore FET sensors.

Cu2O-Mediated Heterojunction Conversion from Dual Type II to Dual Z-Scheme: Its Application in Photoelectric-Colorimetric Dual-Mode Detection of Fat Mass and Obesity-Associated (FTO) Protein

Although the construction of heterojunction has been used in photoelectrochemical (PEC) biosensors, their potential for tunable optical properties has not been deeply explored. Based on the fact that a type-II heterojunction and Z-scheme heterojunction have the same energy band structure, effective alteration of the electron transfer pathway has been achieved by introducing unique photoactive materials into the system and exploiting the interactions between the photomaterials. Based on this, we reported a novel polarity-switchable dual-mode sensor for fat mass and obesity-associated (FTO) protein analysis. Specifically, the MgIn2S4/Bi2MoO6/Bi2S3 dual type-II heterojunction was used as the sensing interface in concert with the rolling circle amplification, CRISPR/Cas12, and terminal DNA transfer enzyme multiamplification strategies, and finally, Cu2O was captured at the sensing interface. Due to the matched energy band, the introduction of Cu2O effectively changed the electron transfer pathway and realized the conversion from a dual type-II heterojunction to a dual Z-scheme heterojunction. It caused the switch of the photocurrent from the anode to the cathode. The developed PEC method showed high sensitivity and selectivity for FTO protein detection in the range of 0.0005-500 μg/L. In addition, based on the peroxidase-like activity of Cu2O to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine by H2O2, the electrode system also achieved the colorimetric detection of FTO protein using the naked eye with the change of the color of the detection solution from colorless to blue. The detection range was from 0.05 to 500 μg/L. This work developed a photoelectrochemical-colorimetric biosensing platform with consciously designed semiconductor structures, revealing the potential of semiconductor-structured transformations in future sensing fields.

Recent progress on DNAzyme-based biosensors for pathogen detection

Pathogens endanger food safety, agricultural productivity, and human health. Those pathogens are spread through direct/indirect contact, airborne transmission and food/waterborne transmission, and some cause severe health consequences. As the population grows and global connections intensify, the transmission of infectious diseases expands. Traditional detection methods for pathogens still have some shortcomings, such as time-consuming procedures and high operational costs. To fulfil the demands for simple and effective detection, numerous biosensors have been developed. DNAzyme, a unique DNA structure with catalytic activity, is gradually being applied in the field of pathogen detection owing to its ease of preparation and use. In this review, we concentrated on the two main types of DNAzyme, hemin/G-quadruplex DNAzyme (HGD) and RNA-cleaving DNAzyme (RCD), explaining their research progress in pathogen detection. Furthermore, we introduced two additional novel DNAzymes, CLICK 17 DNAzyme and Supernova DNAzyme, which showed promising potential in pathogen detection. Finally, we summarize the strengths and weaknesses of these four DNAzymes and offer feasible recommendations for the development of biosensors.

Integrated Photoelectrochemical-SERS Platform Based on Plasmonic Metal-Semiconductor Heterostructures for Multidimensional Charge Transfer Analysis and Enhanced Patulin Detection

Comprehending the charge transfer mechanism at the semiconductor interfaces is crucial for enhancing the electronic and optical performance of sensing devices. Yet, relying solely on single signal acquisition methods at the interface hinders a comprehensive understanding of the charge transfer under optical excitation. Herein, we present an integrated photoelectrochemical surface-enhanced Raman spectroscopy (PEC-SERS) platform based on quantum dots/metal-organic framework (CdTe/Yb-TCPP) nanocomposites for investigating the charge transfer mechanism under photoexcitation in multiple dimensions. This integrated platform allows simultaneous PEC and SERS measurements with a 532 nm laser. The obtained photocurrent and Raman spectra of the CdTe/Yb-TCPP nanocomposites are simultaneously influenced by variable bias voltages, and the correlation between them enables us to predict the charge transfer pathway. Moreover, we integrate gold nanorods (Au NRs) into the PEC-SERS system by using magnetic separation and DNA biometrics to construct a biosensor for patulin detection. This biosensor demonstrates the voltage-driven ON/OFF switching of PEC and SERS signals, a phenomenon attributed to the plasmon resonance effect of Au NRs at different voltages, thereby influencing charge transfer. The detection of patulin in apples verified the applicability of the biosensor. The study offers an efficient approach to understanding semiconductor-metal interfaces and presents a new avenue for designing high-performance biosensors.

Self-validating photothermal and electrochemical dual-mode sensing based on Hg2+ etching Ti3C2 MXene

Mercury ions can cause serious damage to the ecological environment, and it is necessary to develop reliable and elegant mercury ion sensors. In this protocol, a label-free photothermal/electrochemical dual-mode strategy for Hg2+ is proposed based on delaminated Ti3C2 MXene nanosheets (DL-Ti3C2 MXene). Hg2+ exists in water in the form of HgCl2, Hg(OH)2, and HgClOH, and the electron-rich elements O and Cl can specifically bind to the positively charged DL-Ti3C2 MXene at the edge, and further oxidation-reduction reaction occurs to obtain TiO2/C and Hg2Cl2. In view of the reduction activity and the performance of photothermal conversion of DL-Ti3C2 MXene itself, the electrochemical and photothermal responses decrease with the increase of the logarithm of Hg2+ concentration. The corresponding linear ranges are 50 pmol L-1-500 nmol L-1 and 1 nmol L-1-50 μmol L-1, and their detection limits calculated at 3 S/N are 17.2 pmol L-1 and 0.43 nmol L-1, respectively. DL-Ti3C2 MXene has the characteristics of a wide range of raw materials, low cost, and easy preparation. In addition, the design takes full advantage of the properties of the material itself, avoids the complex assembly and detection process of conventional sensors, and enables high selectivity and sensitivity for mercury detection. In particular, the dual-mode sensing endows self-confirmation of mercury ion detection results, thereby improving the reliability of the sensor.

Electrochemical Monitoring of Sphingosine-1-phosphate-Induced ATP Release Using a Microsensor Based on an Entropy-Driven Bipedal DNA Walker

Neuropathic pain is a chronic and severe syndrome for which effective therapy is insufficient and the release of ATP from microglia induced by sphingosine-1-phosphate (S1P) plays a vital role in neuropathic pain. Therefore, there is an urgent demand to develop highly sensitive and selective ATP biosensors for quantitative monitoring of low-concentration ATP in the complex nervous system, which helps in understanding the mechanism involved in neuropathic pain. Herein, we developed an electrochemical microsensor based on an entropy-driven bipedal DNA walker. First, the microsensor specifically recognized ATP via ATP aptamers, initiating the entropy-driven bipedal DNA walker. Subsequently, the bipedal DNA walker autonomously traversed the microelectrode interface, introducing methylene blue to the electrode surface and achieving cascade signal amplification. This microsensor showed excellent selectivity, stability, and a low limit of detection at 1.13 nM. The S1P-induced ATP release from BV2 cells was successfully monitored, and it was observed that dicumarol could inhibit this release, suggesting dicumarol as a potential treatment for neuropathic pain. The microsensor's small size exhibited significant potential for monitoring ATP level changes in neuropathic pain in vivo, which provides a new strategy for in situ and quantitative monitoring of nonelectroactive biomolecules associated with neurological diseases.

A colorimetric and fluorescent dual-mode sensor based on bifunctional G-quadruplex-hemin complex for the determination of Pb2

Due to the threat of lead pollution to health, environmental and food safety, developing simple and fast detection methods is highly required. Whereas, traditional single-mode probe suffers from limited application scenario. In this study, a colorimetric and fluorometric dual-mode probe for Pb2+ determination was constructed by using bifunctional G-quadruplex-hemin complex. In this dual-mode probe, enzyme strand and substrate strand of 8-17 DNAzyme are labeled with G-quadruplex-hemin complex and fluorophore, respectively. In the absence of Pb2+, the self-assembly of enzyme strand and substrate strand inhibits intrinsic mimic peroxidase of G-quadruplex-hemin complex by base-pairing, which also quench the fluorescence via in proximity effect. When the DNAzyme is activated by Pb2+, the quenched fluorescence is restored as well as the inherent peroxidase mimetic activity, leading to dual signal output. Under optimal conditions, this dual-mode probe exhibit a good linear relationship between logarithm of Pb2+ concentration and signal difference within the range from 1.5 nM to 20 nM and 0.5 nM to 10 nM for colorimetric and fluorescence mode, respectively. The detection limits for the corresponding mode were estimated to be 1.29 nM and 0.16 nM, respectively. This dual-mode probe also successfully applied for the spiked river water assay with satisfactory recovery in the range of 93.2 %-115.3 %. This work paves a new way for DNAzyme based dual-mode probe construction.

MXene-Based Chemo-Sensors and Other Sensing Devices

MXenes have received worldwide attention across various scientific and technological fields since the first report of the synthesis of Ti3C2 nanostructures in 2011. The unique characteristics of MXenes, such as superior mechanical strength and flexibility, liquid-phase processability, tunable surface functionality, high electrical conductivity, and the ability to customize their properties, have led to the widespread development and exploration of their applications in energy storage, electronics, biomedicine, catalysis, and environmental technologies. The significant growth in publications related to MXenes over the past decade highlights the extensive research interest in this material. One area that has a great potential for improvement through the integration of MXenes is sensor design. Strain sensors, temperature sensors, pressure sensors, biosensors (both optical and electrochemical), gas sensors, and environmental pollution sensors targeted at volatile organic compounds (VOCs) could all gain numerous improvements from the inclusion of MXenes. This report delves into the current research landscape, exploring the advancements in MXene-based chemo-sensor technologies and examining potential future applications across diverse sensor types.