Self-Powered Temperature Sensor with Seebeck Effect Transduction for Photothermal–Thermoelectric Coupled Immunoassay

Duffy Antigen Receptor for Chemokines (DARC) Nanodisc-Based Biosensor for Detection of Staphylococcal Bicomponent Pore-Forming Leukocidins

Staphylococcus aureus (S. aureus) is an opportunistic infectious pathogen, which causes a high mortality rate during bloodstream infections. The early detection of virulent strains in patients' blood samples is of medical interest for rapid diagnosis. The main virulent factors identified in patient isolates include leukocidins that bind to specific membrane receptors and lyse immune cells and erythrocytes. Duffy antigen receptor for chemokines (DARC) on the surface of specific cells is a main target of leukocidins such as gamma-hemolysin AB (HlgAB) and leukocidin ED (LukED). Among them, HlgAB is a conserved and critical leukocidin that binds to DARC and forms pores on the cell membranes, leading to cell lysis. Current methods are based on ELISA or bacterial culture, which takes hours to days. For detecting HlgAB with faster response and higher sensitivity, we developed a biosensor that combines single-walled carbon nanotube field effect transistors (swCNT-FETs) with immobilized DARC receptors as biosensing elements. DARC was purified from a bacterial expression system and successfully reconstituted into nanodiscs that preserve binding capability for HlgAB. Dynamic light scattering (DLS) and scanning electron microscopy (SEM) showed an increase of the DARC-containing nanodisc size in the presence of HlgAB, indicating the formation of HlgAB prepore or pore complexes. We demonstrate that this sensor can specifically detect the leukocidins HlgA and HlgAB in a quantitative manner within the dynamic range of 1 fM to 100 pM with an LOD of 0.122 fM and an LOQ of 0.441 fM. The sensor was challenged with human serum spiked with HlgAB as simulated clinical samples. After dilution for decreasing nonspecific binding, it selectively detected the toxin with a similar detection range and apparent dissociation constant as in the buffer. This biosensor was demonstrated with remarkable sensitivity to detect HlgAB rapidly and has the potential as a tool for fundamental research and clinical applications, although this sensor cannot differentiate between HlgAB and LukED as both have the same receptor.

A Programmable Microfluidic Paper-Based Analytical Device for Simultaneous Colorimetric and Photothermal Visual Sensing of Multiple Enzyme Activities

New strategies for the simultaneous and portable detection of multiple enzyme activities are highly desirable for clinical diagnosis and home care. However, the methods developed thus far generally suffer from high costs, cumbersome procedures, and heavy reliance on large-scale instruments. To satisfy the actual requirements of rapid, accurate, and on-site detection of multiple enzyme activities, we report herein a smartphone-assisted programmable microfluidic paper-based analytical device (μPAD) that utilizes colorimetric and photothermal signals for simultaneous, accurate, and visual quantitative detection of alkaline phosphatase (ALP) and butyrylcholinesterase (BChE). Specifically, the operation of this μPAD sensing platform is based on two sequential steps. Cobalt-doped mesoporous cerium oxide (Co-m-CeO2) with remarkable peroxidase-like activities under neutral conditions first catalytically decomposes H2O2 for effectively converting colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxidized TMB (oxTMB). The subsequent addition of ALP or BChE to their respective substrates produces a reducing substance that can somewhat inhibit the oxTMB transformation for compromised colorimetric and photothermal signals of oxTMB. Notably, these two-step bioenzyme-nanozyme cascade reactions strongly support the straightforward and excellent processability of this platform, which exhibit lower detection limits for ALP and BChE with a detection limit for BChE an order of magnitude lower than those of the other reported paper-based detection methods. The practicability and efficiency of this platform are further demonstrated through the analysis of clinical serum samples. This innovative platform exhibits great potential as a facile yet robust approach for simultaneous, accurate, and on-site visual detection of multiple enzyme activities in authentic samples.

Enzyme-linked immunoassay for simultaneous detection of methyl parathion and sibutramine in apple cider vinegar

Methyl parathion, a highly toxic, efficient, and persistent organophosphorus pesticide, is widely used in China. Sibutramine, a non-amphetamine central nervous system depressant, helps lose weight by disrupting hormone regulation, stimulating sympathetic nerves, and suppressing appetite. However, some unethical businesses fail to properly handle raw materials in foods like apple cider vinegar, leading to residual methyl parathion in apples or illegal excessive addition of sibutramine. Therefore, it is imperative to develop an immunoassay for the rapid detection of methyl parathion and sibutramine. The corresponding two haptens were prepared and coupled with the carrier proteins according to methyl parathion-sulfur-bovine serum protein (BSA)/chicken ovalbumin (OVA)-sibutramine (20 : 1 : excess, 15 : 1 : excess, 10 : 1 : excess, and 5 : 1 : excess), and sibutramine-BSA/OVA-methyl parathion (20 : 1 : excess, 10 : 1 : excess: 5 : 1 : excess, and 0 : 1 : excess). The result shows that the inhibition rate of the antibody obtained by methyl parathion-BSA/OVA-sibutramine (20 : 1 : excess) was higher than that of sibutramine-BSA/OVA-methyl parathion, which was 67.93%, and the concentration of methyl parathion was 8.65 ng mL-1 at this inhibition rate. Thus, methyl parathion-BSA/OVA-sibutramine (8.65 : 1 : excess) and the corresponding antibodies were selected for subsequent method establishment. By changing the concentration of the coating and antibody, the inhibition rate was found when the coating was 0.125 ng mL-1 and the antibody was diluted 4000 times. The antibody was used to develop a standard curve for the detection of sibutramine at the half-maximum inhibitory concentration (IC50) is 4.59 ng mL-1, the limit of detection (IC10) is 2.21 ng mL-1, the detection range is 2.89 to 7.28 ng mL-1, methyl p-phosphorus at the half-maximum inhibitory concentration (IC50) is 15.34 ng mL-1, the limit of detection (IC10) is 0.42 ng mL-1, the detection range is ng mL-1. Under these conditions, the recovery rate was between 88% and 102%, within reasonable limits, indicating the successful establishment of a rapid enzyme-linked ELISA assay.

Electrochemical immunomagnetic assay for interleukin-6 detection in human plasma

An electrochemical immunoassay for interleukin-6 (IL-6) was developed based on IL-6 capture using magnetic beads and electrochemical signal production using horseradish peroxidase/tetramethylbenzidine. We achieved IL-6 detection from the 50-1000 pg mL-1 range, which is a physiologically relevant IL-6 range for a variety of biological systems. The sandwich assay performed well in phosphate buffered solution as well as in cellular media and human plasma spiked with IL-6, and decreased time to IL-6 concentration readout to approximately one hour. There is also future potential to apply this assay to real-time point-of-care human disease diagnostics.

Zirconium-porphyrin-MOF-based oxidase-like nanozyme with oxygen vacancy for aflatoxin B1 colorimetric sensing

In this study, a porous coordination network zirconium-porphyrin-based nanoparticle with oxygen vacancies (OVs) was prepared using acetic acid and benzoic acid as modulators via a simple hydrothermal method. The presence of OVs was confirmed by various characterization methods and was found to enhance oxygen uptake and activation. This resulted in the generation of more reactive peroxyl radicals (•O2 -) and led to an improved oxidase (OXD) mimetic activity. Additionally, it promoted 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) oxidation, with a low Km value of 0.07 mM and a high Vmax of 1.47 × 10-7 M·s-1. As aflatoxin B1 (AFB1) inhibits the Pt@PCN-222-ABTS nanozyme system, a colorimetric probe for AFB1 detection was constructed. The limit of detection (LOD) was 0.074 µg·L-1. This research presents a novel approach for designing a nanozymatic-based colorimetric method to analyze trace AFB1 residues in food.

Portable hydrogel kit driven by bimetallic carbon dots nanozyme for H2O2-self-supplying dual-modal monitoring of atmospheric CH3SH

Due to the typical volatility of gaseous pollutant methyl mercaptan (CH3SH), the development of a facile, reliable, and accurate onsite environmental surveillance of highly toxic CH3SH faces many challenges, but it is critical to environmental atmosphere assessment and safeguarding public health. Here, we prepared a novel bimetallic carbon dots (Fe&Cu@CDs) nanozyme with high peroxidase-mimicking activity to design a portable hydrogel kit for onsite visual H2O2-self-supplying enzymatic cascade catalytic colorimetric and photothermal signal synergistic amplification dual-modal monitoring of CH3SH in atmospheric environment. Assisted by alcohol oxidase (AOX), CH3SH could be specifically converted into H2O2 for oxidizing chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) catalyzed by Fe&Cu@CDs to produce dark blue ox-TMB with absorption at 652 nm and photothermal characters. Consequently, a CH3SH concentration-dependent change both in naked-eye color and photothermal effect-triggered temperature were observed. By hybridizing AOX-assisted Fe&Cu@CDs + TMB with agarose, a H2O2-self-supplying colorimetric and photothermal signal synergistic amplification sensory hydrogel kit integrated with Color Picker APP-installed smartphone and 660 nm laser-equipped handheld thermal imager for CH3SH was proposed with acceptable results in atmospheric environment around wastepile (e.g., solid waste and food waste piles), which exhibited great potentials to further develop commercial onsite monitoring platforms in warning-early abnormal atmospheric CH3SH for safeguarding environmental health.

Near-infrared responsive gold nanorods for highly sensitive colorimetric and photothermal lateral flow immuno-detection of SARS-CoV-2

The highly infectious characteristics of coronavirus disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), highlight the necessity of sensitive and rapid nucleocapsid (N) protein-based antigen testing for early triage and epidemic management. In this study, a colorimetric and photothermal dual-mode lateral flow immunoassay (LFIA) platform for the rapid and sensitive detection of the SARS-CoV-2 N protein was developed based on gold nanorods (GNRs), which possessed tunable local surface plasma resonance (LSPR) absorption peaks from UV-visible to near-infrared (NIR). The LSPR peak was adjusted to match the NIR emission laser 808 nm by controlling the length-to-diameter ratio, which could maximize the photothermal conversion efficiency and achieve photothermal detection signal amplification. Qualitative detection of SARS-CoV-2 N protein was achieved by observing the strip color, and the limit of detection was 2 ng mL-1, while that for photothermal detection was 0.096 ng mL-1. Artificial saliva samples spiked with the N protein were analyzed with the recoveries ranging from 84.38% to 107.72%. The intra-assay and inter-assay coefficients of variation were 6.76% and 10.39%, respectively. We further evaluated the reliability of this platform by detecting 40 clinical samples collected from nasal swabs, and the results matched well with that of nucleic acid detection (87.5%). This method shows great promise in early disease diagnosis and screening.

Immunoassays and Mass Spectrometry for Determination of Protein Concentrations in Genetically Modified Crops

Quantifying protein levels in genetically modified (GM) crops is crucial in every phase of development, deregulation, and seed production. Immunoassays, particularly enzyme-linked immunosorbent assay, have been the primary protein quantitation techniques for decades within the industry due to their efficiency, adaptability, and credibility. Newer immunoassay technologies like Meso Scale Discovery and Luminex offer enhanced sensitivity and multiplexing capabilities. While mass spectrometry (MS) has been widely used for small molecules and protein detection in the pharmaceutical and agricultural industries (e.g., biomarkers, endogenous allergens), its use in quantifying protein levels in GM crops has been limited. However, as trait portfolios for GM crop have expanded, MS has been increasingly adopted due to its comparable sensitivity, increased specificity, and multiplexing capabilities. This review contrasts the benefits and limitations of immunoassays and MS technologies for protein measurement in GM crops, considering factors such as cost, convenience, and specific analytical needs. Ultimately, both techniques are suitable for assessing protein concentrations in GM crops, with MS offering complementary capabilities to immunoassays. This comparison aims to provide insights into selecting between these techniques based on the user's end point needs.

NIR-II-Absorbing TMB Derivative for 1064 nm-Excited Photothermal Immunoassay

Materials exhibiting strong absorption in the NIR-II region are appealing for photothermal conversion-based imaging, diagnosis, and therapy, due to better thermal effect and decreased absorption of water in such a region. 3,3',5,5'-Tetramethylbenzidine (TMB), the typical substrate in ELISA, has been explored in photothermal immunoassay, since its oxidation product (oxTMB) is photothermally active in the NIR region. However, its absorption at 1064 nm (the most often used laser wavelength in photothermal studies) is not appreciable, thus limiting the assay sensitivity. Here, we proposed a derivative of TMB (3,3'-dimethoxy-5,5'-dimethylbenzidine, 2-OCH3) bearing higher NIR-II absorption for 1064 nm-excited photothermal immunoassay. Since electron-donating groups can help decrease the energy gap of molecules (here -CH3 → -OCH3), the oxidation product of 2-OCH3 exhibited substantially red-shifted absorption as compared with oxTMB, leading to a more than twofold higher absorption coefficient at 1064 nm. As a result, 2-OCH3 showed enhanced sensitivity over TMB in a photothermal immunoassay (PTIA), yielding a limit of detection (LOD) of 0.1 ng/mL for prostate-specific antigen (PSA). The feasibility of 2-OCH3-based PTIA for diagnosis was further validated by analyzing PSA in 61 serum samples. Considering its superior photothermal performance, 2-OCH3 can be explored for a broad range of photothermal applications.

Oxygen Vacancies-Induced Antifouling Photoelectrochemical Aptasensor for Highly Sensitive and Selective Determination of α-Fetoprotein

Accurate measurement of cancer markers in urine is a convenient method for tumor monitoring. However, the concentration of cancer markers in urine is so low that it is difficult to achieve their measurement. Photoelectrochemical (PEC) sensors are a promising technology to realize the detection of trace cancer markers due to their high sensitivity. Currently, the interference of nonspecific biomolecules in urine is the main reason affecting the high sensitivity and selectivity of PEC sensors in detecting cancer markers. In this work, a strategy of oxygen vacancy (OV) modulation is proposed to construct a fouling-resistant PEC aptamer sensing platform for the detection of α-fetoprotein (AFP), a liver cancer marker. The introduction of OVs induces the formation of intermediate localized states in the photoelectric material, which not only facilitates the separation of photogenerated carriers but also leads to the redshift of the light absorption edge. More importantly, OVs with positive electrical properties can be employed to modify the antifouling layer (C-PEG) with negatively charged groups through an electrostatic interaction. The synergistic effect of OVs, antifouling layer, and aptamer resulted in a TiO2/OVs/C-PEG-based PEC sensor achieves a wide linear range from 1 pg/mL to 100 ng/mL and a low detection limit of 0.3 pg/mL for AFP. In addition, the sensor successfully realized the determination of AFP in urine samples and accurately differentiated between normal people and liver cancer patients in the early and advanced stages. This project is of great significance in advancing the application of photoelectrochemical bioanalytical technology to achieve the detection of cancer markers in urine by investigating the construction of an OVs-regulated fouling-resistant sensing interface.

High-Performance Flexible Temperature Sensors Based on Laser-Irradiated Ag-MWCNTs/PEDOT:PSS

Recently, flexible temperature sensors have attracted significant interest due to their wide-ranging applications in areas such as biomedical monitoring, environmental monitoring, electronic skin, and intelligent robots. However, a combination of high sensitivity and high resolution remains a critical challenge. These properties depend on the synthesis techniques of the sensitive materials. In this work, we use a laser irradiation method to prepare a silver nanoparticle-modified carbon nanotube (Ag-MWCNT) which is further mixed with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). The developed temperature sensor exhibited a high sensitivity of -0.45% °C-1 and linearity with an R2 value of 0.998 in the temperature range of 25-80 °C. Additionally, the sensor demonstrated remarkable repeatability, making it suitable for real-time temperature monitoring of the human body and environment. This temperature sensor is successfully demonstrated in practical applications such as monitoring the temperature of various parts of the human body and sensing the spatial temperature. These demonstrations highlight their significant potential in electronic skin and other related fields.

A Portable Self-Powered Electrochemical Sensor Based on Zinc-Air Battery for Detection of Hydrogen Sulfide

The self-powered electrochemical sensor (SPES), an analytical sensing device without external power supply, is integrated with the dual function of power supply and detection performance, which lay the foundation for the development of intelligent and portable electrochemical sensing devices. Herein, a novel SPES based on a zinc-air battery was constructed for the detection of hydrogen sulfide (H2S) in the lysate of colon cancer cells. Typically, an Fe/Fe3C@graphene foam with oxygen reduction performance was used to construct SPES based on a zinc-air battery (ZAB-SPES), which brings the open-circuit voltage to 1.30 V. Among them, the poisoning effect of H2S causes the catalytic performance of the oxygen reduction catalyst to decrease, causing a significant decrease in the discharge voltage of ZAB. Based on this principle, ZAB-SPES was constructed for the detection of H2S using a digital multimeter. The proposed ZAB-SPES demonstrated good selectivity and reproducibility for detecting H2S compared to the results of the H2S-specific fluorescence probe. This strategy enriches the idea of constructing a self-powered sensor and a digital multimeter as detection devices, providing technical support for the portability of SPESs.

Contact-Electro-Catalysis-Assisted Separation via a Dancing PTFE Membrane for Fouling Control

Advanced oxidization processes (AOPs) offer promising solutions for addressing the fouling issues in membrane separation systems. However, the high energy requirements for electrical or light power in the AOPs can be a drawback. In this study, we present a contact-electro-catalysis (CEC)-based approach for controlling membrane fouling, which is stimulated by mild ultrasonic irradiation. During this process, electrons are transferred between a dancing polytetrafluoroethylene membrane and water or oxygen molecules, resulting in the formation of free radicals •OH and •O2-. These free radicals are capable of degrading or inactivating foulants, eliminating the need for additional chemical cleaners, secondary waste disposal, or external stimuli. Furthermore, the time-dependent voltage spikes/oscillations (peak, +7.8/-8.2 V) generate a nonuniform electric field that drives dielectrophoresis, effectively keeping contaminants away from the membrane surface and further enhancing the antifouling performance of the dancing membrane. Therefore, the CEC-assisted membrane separation system offers a green and effective strategy for controlling membrane fouling through mild mechanical stimulation.

Design and use of a wireless temperature measurement network system integrating artificial intelligence and blockchain in electrical power engineering

This work aims to investigate the potential fire hazard stemming from the overheating of power equipment. The advent of the artificial intelligence era has facilitated the fusion of blockchain and Internet of Things (IoT) technologies. This work delves into the technical standards for IoT equipment monitoring and smart grid communication, and the IoT environment of power grid equipment. This work introduces a temperature monitoring network tailored for IoT wireless power equipment suitable for the power environment, and conducts system debugging in the power laboratory. The findings affirm that the temperature out-of-limit alarm testing has met the required criteria, confirming the system's ability to issue timely warnings when temperatures breach a predefined threshold, effectively avoiding high-temperature misfires. This work fully harnesses the secure and user-friendly operation of smart blockchain and the wireless sensing technology of the IoT to realize online monitoring and remote temperature measurement of the power system. It can effectively prevent equipment from overheating and damage, and promote the development of equipment condition monitoring technology in electric power engineering.

Capacitive biosensors for label-free and ultrasensitive detection of biomarkers

Capacitive biosensors are label-free capacitors that can detect biomarkers with the outstanding advantages of simplicity, low cost, and ultrahigh sensitivity. A typical capacitive biosensor consists of a bioreceptor and a transducer, where the bioreceptor captures the biomarker to form a bioreceptor/biomarker conjugate and the transducer generates a detectable signal. In general, antibodies, aptamers, or proteins are exploited as the bioreceptor, while various electrodes including carbon electrodes (CEs), gold electrodes (AuEs), or interdigitated electrodes (IDEs) may serve as the transducer. Because the formation of bioreceptor/biomarker conjugates often leads to a change in capacitance, the capacitive signal is then employed for biomarker detection. This review summarizes recent advances in capacitive biosensors for the detection of biomarkers over the last five years. With a focus on the three common types of bioreceptors, i.e., antibodies, aptamers, and proteins, capacitive biosensors using CEs, AuEs, and IDEs as the transducers are discussed in detail. The immobilization of bioreceptors and signal amplification strategies are described to provide a robust overview of capacitive biosensors for biomarker detection. In addition, analytical methods and future prospects are given to support the application of capacitive biosensors.

Isoniazide modified Ag nanoparticles triggered photothermal immunoassay for carcinoembryonic antigen detection

As the most well-known analytical tool, the thermometer has been extended to the field of biological analysis based on the photothermal effect. Herein, isoniazide modified Ag nanoparticles were prepared as nanolabels to build an immunoassay. The nanoparticles were characterized by transmission electron microscope (TEM), dynamic laser scattering (DLS), X-ray powder diffraction (XRD), and Fourier transform infrared (FT-IR). When the target protein was present, the sandwich immunoassay was developed and the photothermal reaction was triggered by isoniazide modified Ag nanoparticles. As a reducing agent, isoniazide is used to transform phosphomolybdic acid hydrate into molybdenum blue solution. And molybdenum blue had good photothermal stability and high photothermal conversion efficiency. The temperature variation of molybdenum blue solution showed a positive correlation with the concentration of carcinoembryonic antigen (CEA). Thus, the target protein of CEA was quantitative detection by thermometer. The linear response range is 0.1 ng mL-1 to 40 ng mL-1, and the detection limit is 0.08 ng mL-1. Moreover, the proposed protocol had satisfactory selectivity, accuracy, and reproducibility.

Building a Nucleic Acid Nanostructure with DNA-Epitope Conjugates for a Versatile Approach to Electrochemical Protein Detection

The recent surge of effort in nucleic-acid-based electrochemical (EC) sensors has been fruitful, yet there remains a need for more generalizable EC platforms for sensing multiple classes of clinically relevant targets. We recently reported a nucleic acid nanostructure for simple, economical, and more generalizable EC readout of a range of analytes, including small molecules, peptides, proteins, and antibodies. The nanostructure is built through on-electrode enzymatic ligation of three oligonucleotides for attachment, binding, and signaling. However, the generalizable detection of larger proteins remains a challenge. Here, we adapted the sensor to quantify larger proteins in a more generic manner through conjugating the protein's minimized antibody-binding epitope to the central DNA strand. This concept was verified using creatine kinase (CK-MM), a biomarker of muscle damage and several disorders for which rapid clinical sensing is important. DNA-epitope conjugates permitted a competitive immunoassay for the CK protein at the electrode via square-wave voltammetry (SWV). Sensing through a signal-off mechanism, the anti-CK antibody limit of detection (LOD) was 5 nM with a response time as low as 3 min. Antibody displacement by native protein analytes gave a signal-on response with the CK sensing range from the LOD of 14 nM up to 100 nM, overlapping with the normal (nonelevated) human clinical range (3-37 nM), and the sensor was validated in 98% human serum. While a need for improved DNA-epitope conjugate purification was identified, overall, this approach allows the quantification of a generic protein- or peptide-binding antibody and should facilitate future quantitative EC readouts of clinically relevant proteins that were previously inaccessible to EC techniques.

Sensitive Thermography via Sensing Visible Photons Detected from the Manipulation of the Trap State in MAPbX3

Sensitive thermometry or thermography by responding to blackbody radiation is urgently desired in the intelligent information life, including scientific research, medical diagnosis, remote sensing, defense, etc. Even though thermography techniques based on infrared sensing have undergone unprecedented development, the poor compatibility with common optical components and the high diffraction limit impose an impediment to their integration into the established photonic integrated circuit or the realization of high-spatial-resolution and high-thermal-resolution imaging. In this work, we present a sensitive temperature-dependent visible photon detection in Bi-doped MAPbX3 (X = Cl, Br, and I) and employ it for uncooled thermography. Systematic measurements reveal that the Bi dopant introduces trap states in MAPbX3, thermal energy facilitates the carriers jumping from trap states to the conduction band, while the vacancies of trap states ensure the sequential absorption of visible photons with energy less than the band gap. Subsequently, the change of response toward the visible photon is applied to construct the thermograph, and it possesses a specific sensitivity of 2.11% K-1 along temperature variation. As a result, our thermograph presents a temperature resolution of 0.21 nA K-1, a high responsivity of 2.06 mA W-1, and a high detectivity of 2.08 × 109 Jones at room temperature. Furthermore, remote thermal imaging is successfully achieved with our thermograph.

Characterizing a Silver Nanoparticle-Based Electrochemical Biosensor for Shiga Toxin Detection

Shiga toxins (1, 2) regularly cause outbreaks and food recalls and pose a significant health risk to the infected population. Therefore, new reliable tools are needed to rapidly detect Shiga toxin cost-effectively in food, water, and wastewater before human consumption. Enzyme immunoassay and polymerase chain reaction approaches are the gold standard detection methods for the Shiga toxin. However, these methods require expensive instruments along with expensive reagents, which makes them hard to convert into point-of-use and low-cost systems. This study introduces an electrochemical biosensing method that utilizes silver nanoparticles (AgNPs) as electrochemical tags and commercially available low-cost screen-printed carbon electrodes for detection. This study introduces the modification of reference electrodes on commercially available screen-printed carbon electrodes to detect AgNPs dissolved in nitric acid. This biosensor achieved a 2 ng/mL lowest measured concentration for Shiga toxin-1 in less than 3 h. These biosensor results also showed that the AgNP-based sensor has better linearity (for graph between peak current vs concentration) and lower standard deviation compared to gold nanoparticles (AuNP)-based electrochemical biosensors.

Versatile MXene composite probe-mediated homogeneous electrochemiluminescence biosensor with integrated signal transduction and near-infrared modulation strategy for concanavalin A detection

Based on the highly specific interaction between concanavalin A (Con A) and glucose (Glu), a competitive electrochemiluminescence (ECL) biosensor was constructed for ultrasensitive detection of Con A. Nanocomposites with excellent electrocatalytic and photothermal properties were obtained by covalently bonding zinc oxide quantum dots (ZnO QDs) to vanadium carbide MXene (V2C MXene) surfaces. The modification of ZnO QDs hinders the aggregation of V2C MXene and increases the catalytic activity of oxygen reduction reaction, thus amplifying the luminol cathodic emission. In addition, the excellent photothermal performance of the V2C MXene-ZnO QDs can convert light energy into heat energy under the irradiation of 808 nm near infrared laser, thus increasing the temperature of the reaction system and accelerating the electron transfer process to realize the synergistic amplified homogeneous ECL system. This innovative work not only enriches the fundamental research on multifunctional MXene nanomaterials for biosensing, but also provides an effective strategy for ECL signal amplification.

Engineering Entropy-Driven Nanomachine-Mediated Morphological Evolution of Anisotropic Silver Triangular Nanoplates for Colorimetric and Photothermal Biosensing

A DNA/RNA biosensor capable of single nucleotide variation (SNV) resolution is highly desirable for drug design and disease diagnosis. To meet the point-of-care demand, rapid, cost-effective, and accurate SNV detection is of great significance but still suffers from a challenge. In this work, a unique nonenzymatic dual-modal (multicolorimetric and photothermal) visualization DNA biosensor is first proposed for SNV identification on the basis of an entropy-driven nanomachine with double output DNAs and coordination etching of anisotropic silver triangular nanoplates (Ag TNPs). When the target initiates the DNA nanomachine, the liberated multiple output DNAs can be utilized as a bridge to produce a superparamagnetic sandwich complex. The incoming poly-C DNA can coordinate and etch highly active Ag+ ions at the tips of Ag TNPs, causing a shift in the plasmon peak of Ag TNPs from 808 to 613 nm. The more target DNAs are introduced, the more output DNAs are released and thus the more Ag+ ions are etched. The noticeable color changes of anisotropic Ag TNPs can be differentiated by "naked eye" and accurate temperature reading. The programmable DNA nanotechnology and magnetic extraction grant the high specificity. Also, the SNV detection results can be self-verified by the two-signal readouts. Moreover, the dual-modal biosensor has the advantages of portability, cost-effectiveness, and simplicity. Particularly, the exclusive entropy-driven amplifier liberates double output DNAs to bridge more poly-C DNAs, enabling the dual-modal visualization DNA biosensor with improved sensitivity.

Living Anisotropic Structural Color Hydrogels for Cardiotoxicity Screening

Environmental toxins can result in serious and fatal damage in the human heart, while the development of a viable stratagem for assessing the effects of environmental toxins on human cardiac tissue is still a challenge. Herein, we present a heart-on-a-chip based on human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) cultured living anisotropic structural color hydrogels for cardiotoxicity screening. Such anisotropic structural color hydrogels with a conductive parallel carbon nanotube (CNT) upper layer, gelatin methacryloyl (GelMA) interlayer, and inverse opal bottom layer were fabricated by a sandwich replicating approach. The inverse opal structure endowed the anisotropic hydrogels with stable structural color property, while the parallel and conductive CNTs could induce the hiPSC-CMs to grow in a directional manner with consistent autonomous beating. Notably, the resultant hiPSC-CM-cultured hydrogel exhibited synchronous shifts in structural color, responding to contraction and relaxation of hiPSC-CMs, offering a visual platform for monitoring cell activity. Given these features, the hiPSC-CM-cultured living anisotropic structural color hydrogels were integrated into a heart-on-a-chip, which provided a superior cardiotoxicity screening platform for environmental toxins.

Biological redox cycling amplification in a self-powered photoelectrochemical sensor based on TiO2/CdIn2S4/ g-C3N4-WO3 photoanode for sensitive detection of Hg2

A photoelectrochemical (PEC) sensor is proposed with a TiO₂/CdIn₂S₄ co-sensitive structure and a g-C₃N₄-WO₃ heterojunction as the photoanode to form a self-powered system. The photogenerated hole-induced biological redox cycle of TiO₂/CdIn₂S₄/g-C₃N₄-WO₃ composites is used as a signal amplification strategy for Hg²⁺ detection. In the test solution, ascorbic acid is first oxidized by the photogenerated hole of the TiO₂/CdIn₂S₄/g-C₃N₄-WO₃ photoanode, which triggers the ascorbic acid－glutathione cycle to achieve signal amplification and increase the photocurrent. However, in the presence of Hg²⁺, glutathione forms a complex with Hg²⁺, which destroys the biological cycle and leads to a decreased of photocurrent, thus achieving detection of Hg²⁺. Under optimal conditions, the proposed PEC sensor has a wider range (from 0.1 pM to 100 nM), and lower limit of Hg²⁺ detection (0.44 fM) than most other Hg²⁺ detection methods. In addition, the developed PEC sensor can be used to detect of real samples.

The construction of Fe-porphyrin nanozymes with peroxidase-like activity for colorimetric detection of glucose

As a type of nanomaterials with enzyme-mimetic catalytic properties, nanozymes have attracted wide concern in biological detection. H₂O₂ was the characteristic product of diverse biological reactions, and the quantitative analysis for H₂O₂ was an important way to detect disease biomarkers, such as acetylcholine, cholesterol, uric acid and glucose. Therefore, there is of great significance for developing a simple and sensitive nanozyme to detect H₂O₂ and disease biomarkers by combining with corresponding enzyme. In this work, Fe-TCPP MOFs were successfully prepared by the coordination between iron ions and porphyrin ligands (TCPP). In addition, the peroxidase (POD) activity of Fe-TCPP was proved, in detail, Fe-TCPP could catalyze H₂O₂ to produce ·OH by Fenton reaction. Herein, glucose oxidase (GOx) was chosen as the model to build cascade reaction by combining Fe-TCPP to detect glucose. The results indicated glucose could be detected by this cascade system selectively and sensitively, and the limit of detection of glucose was achieved to 0.12 μM. Furthermore, a portable hydrogel (Fe-TCPP@GEL) was further established, which encapsulated Fe-TCPP MOFs, GOx and TMB in one system. This functional hydrogel could be applied for colorimetric detection of glucose by coupling with a smartphone easily.

A pressure-colorimetric multimode system with photothermal activated multiple rolling signal amplification for ovarian cancer biomarker detection

Utilizing the photothermal effect to activate enzyme activity, realize signal conversion and amplification show promising prospects in biosensing. Herein, a pressure-colorimetric multi-mode bio-sensor was proposed through the multiple rolling signal amplification strategy of photothermal control. Under NIR light radiation, the Nb₂C MXene labeled photothermal probe caused notable temperature elevation on a multi-functional signal conversion paper (MSCP), leading to decomposition of thermal responsive element and in-situ formation of Nb₂C MXene/Ag-S_x hybrid. The generation of Nb₂C MXene/Ag-S_x hybrid accompanied with valid color change from pale yellow to dark brown on MSCP. Moreover, the Ag-S_x as a signal amplification element enhanced the NIR light absorption to further improve the photothermal effect of Nb₂C MXene/Ag-S_x thereby induce cyclic in situ production of Nb₂C MXene/Ag-S_x hybrid with rolling enhanced photothermal effect. Subsequently, the continuously enhanced photothermal effect rolling activated catalase-like activity of Nb₂C MXene/Ag-S_x, which accelerated the decomposition of H₂O₂ and promoted the pressure elevation. Therefore, the rolling-enhanced photothermal effect and rolling activated catalase-like activity of Nb₂C MXene/Ag-S_x considerately amplified the pressure and color change. Making full use of multi-signal readout conversion and rolling signal amplification, accurate results can be obtained in a short time, whether in the laboratory or in the patient's homes.

DNA-Driven Photothermal Amplification Transducer for Highly Sensitive Visual Determination of Extracellular Vesicles

Extracellular vesicles (EVs) are crucial focus of current biomedical research and future medical diagnosis. However, the requirement for specialized sophisticated instruments for quantitative readouts has limited the sensitive measurement of EVs to specialized laboratory settings, which in turn has limited bench-to-bedside translation of EV-based liquid biopsies. In this work, a straightforward temperature-output platform based on a DNA-driven photothermal amplification transducer was developed for the highly sensitive visual detection of EVs using a simple household thermometer. The EVs were specifically recognized by the antibody-aptamer sandwich immune-configuration that was constructed on portable microplates. Via a one-pot reaction, cutting-mediated exponential rolling circle amplification was initiated in situ on the EV surface, generating substantial G-quadruplex-DNA-hemin conjugates. Significant amplification in temperature was achieved from the effective photothermal conversion and regulation guided by the G-quadruplex-DNA-hemin conjugates in the 3,3',5,5'-tetramethylbenzidine-H2O2 system. Through obvious temperature outputs, the DNA-driven photothermal transducer enabled highly sensitive EV detection at close to the single-particle level and supported the highly specific identification of tumor-derived EVs directly in serum samples, without the requirement of any sophisticated instrument or labeling process. Benefiting from highly sensitive visual quantification, an easy-to-use readout, and portable detection, this photothermometric strategy is expected to be deliverable across professional on-site screening to home self-testing as EV-based liquid biopsies.

Ag/MoO3–Pd-mediated gasochromic reaction: An efficient dual-mode photoelectrochemical and photothermal immunoassay

Herein, we presented a dual-readout gasochromic immunosensing platform for accurate and sensitive detection of carcinoembryonic antigen (CEA) based on Ag-doped/Pd nanoparticles loaded MoO₃ nanorods (Ag/MoO₃-Pd). Initially, the presence of analyte CEA would prompt the formation of sandwich-type immunoreaction, accompanied by the introduction of Pt NPs labeled on detection antibody. Upon the addition of NH₃BH₃, the product hydrogen (H₂) will interact with Ag/MoO₃-Pd as a bridge between the sensing interface and the biological assembly platform. Both photocurrent and temperature signals can serve as readouts due to the significantly increased PEC performance and enhanced photothermal conversion capability of H-Ag/MoO₃-Pd (the product of Ag/MoO₃-Pd react with H₂) compared to Ag/MoO₃-Pd. In addition, the DFT results show that the band gap of Ag/MoO₃-Pd becomes narrower after the reaction with H₂, thus improving the utilization of light, which theoretically explains the internal mechanism of gas sensing reaction. Under optimal conditions, the designed immunosensing platform showed good sensitivity for CEA detection with the limit of detection (LOD) of 26 pg mL^-1 (photoelectrochemical mode) and 98 pg mL^-1 (photothermal mode). This work not only presents the possible reaction mechanism of Ag/MoO₃-Pd and H₂, but also creatively applicate it in photothermal biosensors that give a new path for devising dual-readout immunosensor.

Fascinating Immobilization-Free Electrochemical Immunosensing Strategy Based on the Cooperation of Buoyancy and Magnetism

Rapid and accurate detection of biomolecules is of vital importance for the diagnosis of disease and for performing timely treatments. The point-of-care analysis of cancer biomarkers in the blood with low cost and easy processing is still challenging. Herein, an advanced and robust strategy, which integrates the buoyant recognition probe with the magnetic reporter probe in one solution, was first proposed for immobilization-free electrochemical immunosensing. The tumor marker of alpha fetoprotein (AFP) can be captured immune-buoyantly, and then a multifunctional magnetic reporter probe in pseudo-homogeneous solution was further captured to fulfill a sandwich-type immunoreaction. The residual magnetic reporter probe can be firmly and efficiently attracted on a magnetic glassy carbon electrode to fulfill the conversion of the target AFP amount into the residual magnetic electrochemical signal indicator. As a result, the electrochemical signal of methylene blue can accurately reflect the original level of target antigen AFP concentration. By integrating buoyancy-driven quasi-homogenous biorecognition with magnetism-mediated amplification and signal output, the proposed immobilization-free electrochemical immunosensing strategy displayed a wide range of linear response (100 fg mL^-1 to 10 ng mL^-1), low detection limit (14.52 fg mL^-1), and good reproducibility, selectivity, and stability. The designed strategy manifests remarkable advantages including assay simplicity, rapidness, and high sensitivity owing to the in-solution instead of on-electrode biorecognition that could accelerate and improve the biorecognition efficiency. To the best of our knowledge, this is the first cooperation of buoyancy-driven biorecognition with magnetism-mediated signal output in bioanalysis, which would be attractive for rapid clinic biomedical application. Thus, this work provides a fresh perspective for convenient and favorable immobilization-free electrochemical biosensing of universal biomolecules.

The target-induced redox and diazotized reaction for colorimetric ratio detection of nitrite using CoOOH nanosheets as mimetic oxidase

Nitrite is a commonly used food additive and water contaminant that has received widespread attention due to its harmful effects on humans. Here, a colorimetric ratio sensing platform for the detection of nitrite in foods as well as aquatic systems was developed via the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by CoOOH nanosheets (CoOOH NSs). Interestingly, in the presence of nitrite, TMB complexes in acidic environments can be oxidized and diazotized to produce yellow oxidized TMB (oxTMB) and diazotized TMB, resulting in the nitrite concentration-dependent ratio variation for the absorbance peaks at 655 and 450 nm (A₆₅₅/A₄₅₀). The colorimetric ratio sensing offers higher sensitivity and better selectivity compared to conventional detection methods because of the specific target-induced reduction-oxidation and diazotized reaction, as well as the excellent mimetic oxidase activity of CoOOH NSs. Based on this strategy, a smartphone-assisted portable approach was designed for the in-situ/visual detection of nitrite, which has good application prospects.

Near Infrared-II Photothermal and Colorimetric Synergistic Sensing for Intelligent Onsite Dietary Myrosinase Profiling

Myrosinase (Myr) is a type of critical β-thioglucosidase enzyme activator essential for sustaining many functional foods to perform their health-promoting functions. An accurate and reliable Myr test is meaningful for food quality and dietary nutrition assessments, whereas the currently reported methods do not guarantee specificity and have high reliance on instrumentation, which are not suitable for rapid and onsite Myr screening especially in complex systems from various sources. Herein, we present a unique NIR-II absorption-based photothermal-responsive colorimetric biosensor for anti-interference onsite Myr determination and realization of rapid visualized outputs with the aid of smartphone calculation. Typically, assisted by glucose oxidase (GOx), Myr specifically converts the sinigrin substrate into hydrogen peroxide (H₂O₂) that can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) catalyzed by AuNPs to form a charge transfer complex (CTC) with NIR-II absorption and photothermal characters. Delightfully, such a proposed method is able to determine Myr within a wide range of 0 to 172.5 mU/mL with a detection limit down to 2.96 mU/mL. Moreover, simple, rapid, and real-time visual Myr identification in actual food-sourced samples could also be readily achieved by smartphone readout processing, with the promising advantages of anti-interference, high accuracy, and low cost as well as labor-saving and intelligence engagement, thus providing great feasibility for precise measurement in complex and dynamic dietary sample analysis. Overall, our proposed method presents a novel technology for onsite dietary Myr enzyme profiling, which is promising to be applied in the food industry for nutritional composition profiles, freshness evaluation, and quality assessment.

Kinetics-accelerated one-step detection of MicroRNA through spatially localized reactions based on DNA tile self-assembly

The localization of isothermal amplification systems has elicited extensive attention due to the enhanced reaction kinetics when detecting ultra-trace small-molecule nucleic acids. Therefore, the seek for an appropriate localization cargo of spatially confined reactions is urgent. Herein, we have developed a novel approach to localize the catalytic hairpin assembly (CHA) system into the DNA tile self-assembly nanostructure. Thanks to the precise programming and robust probe loading capacity, this strategy achieved a 2.3 × 10⁵-fold higher local reaction concentration than a classical CHA system with enhanced reaction kinetics in theory. From the experimental results, this strategy could reach the reaction plateau faster and get access to a magnified effect of 1.57-6.99 times higher in the linear range of microRNA (miRNA) than the simple CHA system. Meanwhile, this strategy satisfied the demand for the one-step detection of miRNA in cell lysates at room temperature with good sensitivity and specificity. These features indicated its excellent potential for ultra-trace molecule detection in clinical diagnosis and provided new insights into the field of bioassays based on DNA tile self-assembly nanotechnology.

Carbon Nanotube-Incorporated Nanofibers for Immunosensor Preparation against CD36

The increased serum concentration of CD36 is significantly associated with atherosclerosis, insulin resistance, and diabetes mellitus. Currently, there is no sensor system used for the detection of CD36 in the clinical field. Therefore, there is a need to develop a sensor system for the detection of CD36. The large surface area/volume ratio and controllable surface conformation of electrospun nanofibers (ENs) make them highly attractive for immunosensor applications. In the present study, PS/MWCNT-PAMAM ENs were produced and used as an immobilization matrix of Anti-CD36. Thus, the electrochemical behavior of the developed nanocomposite-based ENs and their usage potential were investigated for immunosensor applications. First, an oxidized multiwall carbon nanotube (MWCNT-OH) was synthesized and modified with a polyamidoamine generation 3 (PAMAM G3) dendrimer. The synthesized MWCNT-PAMAM nanocomposite was mixed with polystyrene (PS) solutions at different ratios to produce bead-free, smooth, and uniform PS/MWCNT-PAMAM ENs. PS/MWCNT-PAMAM ENs were accumulated on a screen-printed carbon electrode (SPCE) using the electrospinning technique. A biofunctional surface on the PS/MWCNT-PAMAM EN-coated SPCE was created using carbodiimide chemistry by covalent immobilization of Anti-CD36. The analytic performance characteristics of the developed PS/MWCNT-PAMAM/Anti-CD36 immunosensor were determined by performing electrochemical measurements in the presence of the CD36 protein. The linear detection range was found to be from 5 to 40 ng/mL, and the limit of detection was calculated as 3.94 ng/mL for CD36. The developed PS/MWCNT-PAMAM/Anti-CD36 immunosensor also displayed high tolerance to interference substances, good repeatability, and high recovery percent (recovery%) for artificial blood serum analysis.

Regenerative Strategy of Gold Electrodes for Long-Term Reuse of Electrochemical Biosensors

Gold is of considerable interest for electrochemical active surfaces because thiol-modified chemicals and biomolecules can be easily immobilized with a simple procedure. However, most gold surfaces are damaged with repetitive measurements, so they are difficult to reuse. Here we demonstrate a novel electrochemical cleaning method of gold surfaces to reuse electrodes with a simple protocol that is easy and nontoxic. This electrochemical cleaning consists of two steps by using different solutions. The 1st step is a cyclic voltammetry sweep using a very low concentration of sulfuric acid, and the 2nd step is a cyclic voltammetry sweep using potassium ferricyanide. Different cleaning methods were also considered for comparison. Consequently, after assembling and desorption of the cell and antigen, the changes in gold electrode performance, as immunosensor and cytosensor, were investigated by electrochemical impedance and cyclic voltammetry. It was found that repetitive measurement is possible until five times while maintaining the reproducibility. It is believed that this method is capable of enabling reuse of gold electrodes and can be used for long-term and accurate monitoring of biological effects, especially at a low cost.

Gas-Mediated Immunoassay for the Carcinoembryonic Antigen at Atmospheric Pressure with Smartphone Coupling with the Fluorescence Quenching Length of Perovskite Capillary

By combining the photothermal properties of the 3,3',5,5'-tetramethylbenzidine oxidation product (TMBox) with the sensitive quenching of perovskite fluorescence by ammonia gas, a gas-mediated immunoassay at atmospheric pressure was constructed, which took the fluorescence quenching length of perovskite fluorescent capillary as the signal output. First, a CsPbBr₃ perovskite with surface modification of 3-aminopropyl triethoxysilane was synthesized by thermal injection and decorated to the capillary wall by glutaraldehyde cross-linking. In the presence of H₂O₂ and the tumor marker carcinoembryonic antigen (CEA), TMB was oxidized to TMBox by the horseradish peroxidase (HRP)-labeled CEA antibody. The photothermal effect of TMBox at 808 nm laser irradiation increases the concentration of ammonia gas, and the prepared fluorescent capillary can respond sensitively to ammonia gas. The fluorescence quenching length can be observed by the naked eye for a semiquantitative evaluation of CEA concentration. At the same time, we developed a mobile APP for the first time to measure the fluorescence quenching length. In the range of 0-20 ng mL^-1, the quenching length increased linearly with the increase in CEA concentration, and the detection limit was 0.078 ng mL^-1. This method has been successfully used for the detection of CEA in human serum with a recovery of 95.8%-106.5%.

Metal sulfide nanoparticle-based dual barcode-triggered DNAzyme cascade for multiplex miRNA detection in a single assay

Single miRNAs are not specific and accurate enough to meet the strict diagnosis requirements in practice. Therefore, simultaneous monitoring of multiplexed miRNA in biological samples can not only improve the accuracy and specificity of bioassays but also avoid the squandering of valuable biological specimens. Herein, we designed a metal sulfide nanoparticle-based dual barcode-triggered DNAzyme cascade strategy for the sensitive and simultaneous multiplex miRNA detection in a single assay. Firstly, the capture probes (H1, H2) specifically recognize targets (miRNA-21, miRNA-141), exposing the stem of H1 and H2. Then, with the introduction of a detection probe (CuS-H3, ZnS-H4), the exposed H1 and H2 catalyze the hairpin assembly (CHA) reaction, realizing target miRNA recycling, and forming H1/H3-CuS and H2/H4-ZnS complexes. Subsequently, the formed H1/H3-CuS and H2/H4-ZnS complexes are encoded on magnetic beads through the biotin/streptavidin interaction. The CuS and ZnS nanoparticles captured by magnetic beads release thousands of Cu²⁺ and Zn²⁺via the cation exchange reaction. Finally, the released Cu²⁺ and Zn²⁺ specially activate the DNAzyme of the catalytic and molecular beacon (CAMB) system. The CAMB system affords an amplified fluorescence signal output by cycling and regenerating the metal ion-dependent DNAzyme to realize multiple enzymatic turnovers. Benefiting from target recycling, nanoparticle amplification, and catalytic and molecular beacon amplification, there is substantial amplification and the target miRNAs can be detected at 0.06 fM (miRNA-21) and 0.048 fM (miRNA-141) in a single assay. Furthermore, the high selectivity and accuracy of the assay were proved by practical analysis of different cancer cells, which exhibited good practicability in multiplex miRNA detection in clinical sera. The results indicate that the proposed strategy holds great potential for the sensitive detection of multiplex cancer biomarkers and offers the opportunity for future applications in clinical diagnosis.

Recent Progress and Challenges on the Microfluidic Assay of Pathogenic Bacteria Using Biosensor Technology

Microfluidic technology is one of the new technologies that has been able to take advantage of the specific properties of micro and nanoliters, and by reducing the costs and duration of tests, it has been widely used in research and treatment in biology and medicine. Different materials are often processed into miniaturized chips containing channels and chambers within the microscale range. This review (containing 117 references) demonstrates the significance and application of nanofluidic biosensing of various pathogenic bacteria. The microfluidic application devices integrated with bioreceptors and advanced nanomaterials, including hyperbranched nano-polymers, carbon-based nanomaterials, hydrogels, and noble metal, was also investigated. In the present review, microfluid methods for the sensitive and selective recognition of photogenic bacteria in various biological matrices are surveyed. Further, the advantages and limitations of recognition methods on the performance and efficiency of microfluidic-based biosensing of photogenic bacteria are critically investigated. Finally, the future perspectives, research opportunities, potential, and prospects on the diagnosis of disease related to pathogenic bacteria based on microfluidic analysis of photogenic bacteria are provided.

Dual-mode colorimetric-photothermal sensing platform of acetylcholinesterase activity based on the peroxidase-like activity of Fe-N-C nanozyme

Sensors based on colorimetry, fluorescence, and electrochemistry have been widely employed to detect acetylcholinesterase and its inhibitors, however, there are only a minority of strategies for AChE detection based on photothermal method. This work reports a versatile dual-mode colorimetric and photothermal biosensing platform for acetylcholinesterase (AChE) detection and its inhibitor (paraoxon-ethyl, a model of AChE inhibitors) monitor based on Fe-N-C/H₂O₂/3,3',5,5'-tetramethylbenzidine (TMB) system. The Fe-N-C with abundant active Fe-Nx sites shows outstanding peroxidase-mimicking activity and can be used to promote the generation of •OH by H₂O₂ to oxidize TMB. However, the introduction of mercapto molecules tending to coordinate with metal atoms result in the block of action site in Fe-N-C, thereby decrease its peroxidase-mimetic activity. The designed biosensor principle is based on the block of active sites of Fe-N-C by thiocholine (TCh, one kind of mercapto molecules) that can be produced by acetylthiocholine (ATCh) in the presence of AChE. Under optimum conditions, the limit of detection (LOD) for AChE activity is 1.9 mU mL^-1 (colorimetric) and 2.2 mU mL^-1 (photothermal), while for paraoxon-ethyl is 0.012 μg mL^-1 (colorimetric) and 0.013 μg mL^-1 (photothermal), respectively. The assay we proposed not only can be designed to monitor AChE detection and its inhibitors, but also can be easily extended for the detection of other biomolecules relate to the generation or consumption of H₂O₂.

Ultrathin Covalent Organic Framework Nanosheets/Ti3C2Tx-Based Photoelectrochemical Biosensor for Efficient Detection of Prostate-Specific Antigen

Designable and ultrathin covalent organic framework nanosheets (CONs) with good photoelectric activity are promising candidates for the construction of photoelectrochemical (PEC) biosensors for the detection of low-abundance biological substrates. However, achieving highly sensitive PEC properties by using emerging covalent organic framework nanosheets (CONs) remains a great challenge due to the polymeric nature and poor photoelectric activity of CONs. Herein, we report for the first time the preparation of novel composites and their PEC sensing properties by electrostatic self-assembly of ultrathin CONs (called TTPA-CONs) with Ti₃C₂T_x. The prepared TTPA-CONs/Ti₃C₂T_x composites can be used as photocathodes for PEC detection of prostate-specific antigen (PSA) with high sensitivity, low detection limit, and good stability. This work not only expands the application of CONs but also opens new avenues for the development of efficient PEC sensing platforms.

Polydopamine-Functionalized Copper Peroxide/ZIF-8 Nanoparticle-Based Fluorescence-Linked Immunosorbent Assay for the Sensitive Determination of Carcinoembryonic Antigen by Self-Supplied H2O2 Generation

Copper peroxide/zeolitic imidazolate framework/polydopamine nanoparticles (CP/ZIF-8/PDA)-based fluorescence-linked immunosorbent assay (FLISA) was designed for the sensitive and high-throughput determination of carcinoembryonic antigen (CEA) by self-supplied H₂O₂ generation. Specifically, the CEA aptamer was modified on the surface of CP/ZIF-8/PDA to form an immunoprobe. The structures of CP and ZIF-8 could be broken under acidic conditions, and produced the Cu²⁺ and H₂O₂ due to the dissociation the CP. A subsequent Fenton-type reaction of Cu²⁺ and H₂O₂ generated hydroxyl radical (·OH). o-phenylenediamine (OPD) was oxidized by the ·OH to form 2, 3-diaminophenazine (DPA) with a significant fluorescence signal. CP/ZIF-8/PDA could be used as an efficient Fenton-type reactant to generate a large amount of ·OH to promote OPD oxidation. The sensitive detection of CEA could be realized. Under optimal conditions, the FLISA platform displayed a linear detection range from 0.01 to 20 ng mL^-1 with a detection limit of 7.6 pg mL^-1 for CEA. This strategy has great application potential for sensitive and high-throughput determination for other biomarkers in the field of biomedicine.

Point-of-Care Immunoassay Based on a Multipixel Dual-Channel Pressure Sensor Array with Visual Sensing Capability of Full-Color Switching and Reliable Electrical Signals

The point-of-care (POC) method with affordability and portability for the sensitive detection of biological substances is an emerging topic in rapid disease screening and personalized medicine. In this work, we demonstrated a diverse responsive platform based on a dual-channel pressure sensor (DCPS). The DCPS had a multilayer flexible architecture consisting of a photonic hydrogel with chromatic transitions and a piezoresistive pressure sensor as the electrical data transmission unit, both of which had the property of pressure-induced mechanical stimulus feedback. By incorporating a platinum nanoparticles-labeled detection antibody (PtNPs-dAb) into the sandwich-type immunoreaction for the target carcinoembryonic antigen (CEA, as a model analyte), gas decomposition could be triggered by the addition of hydrogen peroxide (H₂O₂) to induce a significant increase under pressure in a closed chamber. Meanwhile, the DCPS enabled an accurate electrical signal output, and the photonic hydrogel converted spatiotemporal stimuli into eye-readable colorations with string brilliance. In this way, the target concentration could be quantificationally related to the electrical response and intuitively perceived through visible color alterations. Under optimal conditions, a sensitive determination of CEA was performed in a detectable range of 0.3-60 ng/mL with a limit of detection (LOD) of 0.13 ng/mL. In addition, the proposed protocol had satisfactory selectivity, accuracy, and reproducibility. Furthermore, an array-based immunoassay device was fabricated to conceptually validate its application potential in high-throughput biomedical detection and inspire a dual-signal POC diagnostic platform in a friendly way for resource-limited settings.

Flexible and High-Throughput Photothermal Biosensors for Rapid Screening of Acute Myocardial Infarction Using Thermochromic Paper-Based Image Analysis

Herein, we developed a flexible, low-cost thermosensitive fiber paper for the visual display in photothermal biosensing systems for early acute myocardial infarction. The thermal signal visualization device was encapsulated with rewritable thermal fibers, which exhibited excellent stability and reversibility. The mechanism of color change in thermal paper was based on a temperature-driven reversible transformation of the structure of the dye molecule (crystalline violet lactone, CVL). It exhibits a gradation from blue to colorless at higher temperatures and gradually returns to blue when the temperature drops. Immobilization and cascade enzymatic reactions of target molecules occurred in an integrated 3D-printed detection device, a photothermal conversion process occurred under near-infrared light excitation, and the colorimetric change values of the encapsulated thermal paper were recorded and evaluated for possible pathogenicity using a smartphone. It was worth noting that the effect of the thermogenic ring-opening behavior of CVL on the macroscopic phenomenon of color change was obtained by density functional theory calculations. Under optimized conditions, the naked-eye-recognizable range of the thermal paper-based photothermal immunoassay sensor was 0.2-20 ng mL^-1, This work creatively presents theoretical studies of promising thermal paper-based photothermal biosensors and provides new insights for the development of low-cost, instrument-free portable photothermal biosensors.