Chemiluminescence-Derived Self-Powered Photoelectrochemical Immunoassay for Detecting a Low-Abundance Disease-Related Protein

Reconfiguration/Immobilization "Dual-Free" Self-Powered Multiplex Photoelectrochemical Strategy for Dual Magnetic Bead-Mediated Dimension Differentiate Type Complex Sample Assay

Despite significant advances in single-interface multiplex photoelectrochemical (PEC) sensors, their potential in high-throughput complex sample analysis is still limited by time-consuming immobilization and cumbersome surface reconfiguration procedures. Particularly for the rapidly growing demand for point-of-care testing, there is an urgent need to explore fast, low-consumption, and sustainable multisignal differentiation approaches ready for implantation into a portable sensor. Herein, a dual magnetic bead-mediated reconfiguration/immobilization "dual-free" strategy is proposed for self-powered PEC sensing of multiple targets on a single electrode. The dual magnetic bead-mediated dimension-differentiated system is formed by two size-differentiated magnetic beads (MBs) and methylene blue-loaded liposomes (MLLs). A large MB is involved in obtaining the MLL signal label via magnetic separation, which modulates the electron transfer mechanism and generates a detection signal. After physically controlled release, the small MB (second signal label) magnetically anchors at the electrode interface to produce another detection signal. By circumventing chemical immobilization and interface reconfiguration, the "dual-free" strategy realizes the rapid, low-cost, sequential, and nondestructive detection of coexisting antibiotics (kanamycin and tobramycin). To further reduce the dimensions and power consumption of the sensing device, a self-powered dual-photoelectrode system is established and instrumented. The reconfiguration/immobilization "dual-free" self-powered sensor eliminates cross-interference, preserves electrode integrity, and avoids external power requirements, thereby pioneering a universal approach for developing miniaturized PEC sensors with great promise for point-of-care testing.

Polarity-Switchable Dual-Mode Photoelectrochemical Cancer Marker Immunoassay Based on a Metal-Organic Framework@Nitrogen-Doped Graphdiyne Heterojunction

A photocurrent polarity-switching photoelectrochemical (PEC) assay has been used for its anti-interference ability and superior accuracy compared to a conventional PEC measuring system. In this work, an ultrasensitive photocurrent polarity-switchable assay was established for sensitive prostate-specific antigen (PSA) detection based on a novel metal-organic framework (MOF) and graphdiyne@polyaniline (GDY@PANI)-sensitized structure as a photoactive material. The nitrogen-doped carbon nanolayers wrapped around graphdiyne and a zinc-based MOF were synthesized via a hydrothermal method. As an excellent photoactive material, the type II heterostructure (MOF/GDY@PANI) not only reduced the recombination of generated electron-hole pairs but also resulted in a significant increase in photoelectric conversion efficiency. Furthermore, its photocurrent was 4.6-fold higher than that of GDY@PANI and 37-fold higher than the proposed MOF. The integrated MOF/GDY@PANI/antibody (Ab) glassy carbon photoelectrode (GCE) was used as a PEC immunosensor for PSA detection (signal-off mode) and exhibited a wide linear dynamic range from 0.1 fg/mL to 10 pg/mL and a limit of detection of 0.05 fg/mL. The GCE modified with MOF and primary antibody (Ab1) (GCE/MOF/Ab1) produced a cathodic photocurrent, and in the presence of PSA, after the introduction of GDY@PANI-labeled-secondary antibody (Ab2) onto the surface of GCE/MOF/Ab1 and formation of an immunocomplex, the photocurrent amplified and switched to an anodic current. Due to high photoelectric conversion efficiency and good polarity-switching ability of GDY@PANI, the proposed immunosensor presented a turn-on photoelectrochemical performance for PSA detection at a wide linear range from 0.1 to 10 pg/mL and ultralow detection limit of 0.03 fg/mL. Compared to signal-off mode, the sensitivity increased 2-fold and the effect of interferences produces more reliable results due to photocurrent switching, and its effectiveness was evaluated against an enzyme-linked immunosorbent assay (ELISA) using spiked real human serum samples. The positive and promising outcomes achieved by the proposed immunosensor imply that the developed platform has the potential to serve as an excellent enzyme-free photoanode immunosensor for early cancer diagnosis and therapeutic monitoring.

Crystal Facet Engineering Modulated Electron Transfer Mechanisms: A Self-Powered Photoelectrochemical Sensing Platform for Noninvasive Detection of Uric Acid

Crystal facet engineering is a pivotal strategy to design high-performance photoelectrodes and suppress electron and hole complexation, thus enhancing photoelectrochemical (PEC) activity through carrier enrichment at specific crystal facets. However, there is still a lack of systematic resolution on the intrinsic principles of crystal facet tuning energy band structure and the specific adsorption of signaling molecules. In this work, a multidimensional synergistic optimization strategy was proposed to achieve precise prediction and targeted crystal facet design of photoelectrodes by establishing a quantitative structure-activity relationship (QSAR) model of "crystal configuration-molecular recognition-carrier transport". A three-dimensional hierarchical TiO2 nanoflower (3D HTNF) photoelectrode dominated by the {110} facet exhibited a significant positive photocurrent toward uric acid (UA). Integrated with a microelectromechanical system (MEMS), a miniaturized self-powered PEC biosensor provided an innovative solution for high-throughput, noninvasive UA monitoring in saliva and displayed a linear range of 0.01-50 μM with a detection limit of 8.76 nM. In addition, the advantages of photoelectrodes in light harvesting, charge separation and migration, molecular adsorption, and surface reactions were verified by density functional theory (DFT) calculations to reveal the path selectivity and carrier transport mechanisms of the photo-oxidation reactions on specific crystal surfaces. This study elucidates the interplay mechanism of the crystal surface tuning energy band structure and the interfacial kinetics of response. The program can be extended to precisely detect biomarkers in complex biological matrices, promoting the leapfrog development of noninvasive health monitoring technology.

Inflammatory microenvironment-responsive electrochemical biosensing for cancer cell discrimination using PtZnCd-anchored multi-walled carbon nanotubes

The quantification of intracellular hydrogen peroxide (H2O2) serves as a critical biomarker for characterizing cellular physiological states, providing essential insights into metabolic regulation and signaling pathways. This analytical paradigm not only advances our understanding of pathological mechanisms but also contributes to the development of novel diagnostic approaches and precision therapeutic interventions. Herein, we established an innovative electrochemical microsensing platform capable of discriminating between malignant and normal cells through their distinct inflammatory responses under external stimulation. This innovative methodology integrates three critical technical advancements: (i) optimization of a one-pot microwave synthesis protocol for fabricating high-performance PtZnCd nanoparticles anchored on multi-walled carbon nanotubes (MWCNTs), which serve as the core sensing element; (ii) systematic electrochemical characterization coupled with density functional theory (DFT) calculations demonstrating that this hybrid architecture significantly reduces interfacial charge-transfer resistance while enhancing heterogeneous electron transfer kinetics; (iii) comprehensive biocompatibility evaluations confirming the composite material's favorable cytotoxicity profile and biological safety, supporting its potential for cellular classification applications. Through real-time monitoring of dynamic metabolic fluctuations and intracellular inflammatory microenvironment changes in response to ascorbic acid (AA) and dehydroascorbic acid (DHA) stimulation, we established distinct response signatures that effectively differentiate neoplastic cells from their healthy counterparts. This study introduces an innovative electrochemical sensing paradigm that synergistically combines biocompatible nanocatalysts with inflammatory microenvironment dynamics, establishing a robust platform for dual discrimination between cancerous and normal cells, with significant implications for biomedical research and clinical diagnostics.

Liquid Biopsy on Microfluidics: From Existing Endogenous to Emerging Exogenous Biomarkers Analysis

Liquid biopsy is an appealing approach for early diagnosis and assessment of treatment efficacy in cancer. Typically, liquid biopsy involves the detection of endogenous biomarkers, including circulating tumor cells (CTCs), extracellular vesicles (EVs), circulating tumor DNA (ctDNA), circulating tumor RNA (ctRNA), and proteins. The levels of these endogenous biomarkers are higher in cancer patients compared to those in healthy individuals. However, the clinical application of liquid biopsy using endogenous biomarker analysis faces challenges due to its low abundance and poor stability in circulation. Recently, a promising strategy involving the engineering of exogenous probes has been developed to overcome these limitations. These exogenous probes are activated within the tumor microenvironment, generating distinct exogenous markers that can be easily distinguished from background biological signals. Alternatively, these exogenous probes can be labeled with intrinsic endogenous biomarkers in vivo and detected in vitro after metabolic processes. In this review, we primarily focus on microfluidic-based liquid biopsy techniques that allow for the transition from analyzing existing endogenous biomarkers to emerging exogenous ones. First, we introduce common endogenous biomarkers, as well as synthetic exogenous ones. Next, we discuss recent advancements in microfluidic-based liquid biopsy techniques for analyzing both existing endogenous and emerging exogenous biomarkers. Lastly, we provide insights into future directions for liquid biopsy on microfluidic systems.

Robust nCuO modulated by defect engineering enhanced photoelectrochemical biosensor for the detection of miRNA-21

Traditional p-type CuO (pCuO), valued for its tunable band gap and p-type conductivity, has been widely used in photoelectrochemical biosensors. However, its weak conductivity leads to unsatisfied photoelectrochemical signals and limits its use in in situ vulcanization reactions. We synthesized n-type CuO (nCuO) with abundant oxygen vacancies through a simple chemical reduction for the first time, which was applied as efficient photoactive material. The resulting nCuO exhibits superior photoelectrochemical performance than pCuO, thanks to enhanced carrier separation facilitated by the oxygen vacancies. Upon miRNA-21 introduction, H₂S was generated, which can react with Cu(II) to form nCuO-pCuS heterojunction on the electrode. Inspiringly, the current increase of nCuO is 2.3 times higher than the pCuO after vulcanization reaction due to the built-in electric field of the nCuO-pCuS heterojunction can promote efficient carrier separation. Under optimal conditions, the biosensor offers excellent analytical performance, with a wide linear range (0.004-400 pM) and a detection limit of 1.8 fM. The integration of oxygen defect engineering and target-triggered vulcanization presents a new strategy for designing high-performance photoelectrochemical biosensors.

Overcoming kinetic barriers of remote electrochemiluminescence on boron-doped diamond via catalytic coreactant oxidation

The effectiveness of boron-doped diamond (BDD) as a platform for electrochemiluminescence (ECL) bead-based bioassays is hindered by the sluggish rate of heterogeneous tri-n-propylamine (TPrA) oxidation. To address this, we investigate the ECL of Ru(II)-coated microbeads in the presence of a redox mediator, exploring the effect of applied potential and electrode surface terminations. Using a redox mediator, the ECL signal on BDD is enhanced by up to 46-fold.

Development of a Cell-Free, Toehold Switch-Based Biosensor for Rapid and Sensitive Zika Virus Detection

The need for rapid and sensitive diagnostic tools is emphasized by the significant impact of infectious diseases on global health. This study presents a cell-free biosensor utilizing toehold switch technology, combined with nucleic acid sequence-based amplification (NASBA), for high specificity and sensitivity in Zika virus detection. The toehold switch, a denovo-designed regulator of gene expression, forms the crux of our detection system, offering a versatile and programmable approach to nucleic acid-based diagnostics. The cell-free system based on Escherichia coli extract served as the platform for sensor expression, enabling real-time monitoring and optimization of the reaction conditions for minimal background leakage and maximal activation efficiency. The performance of the toehold switch sensor was rigorously evaluated through a series of tests, revealing that switch S23 demonstrated the most promising activation effects and sequence specificity. Notably, the integration of NASBA technology significantly enhanced the detection sensitivity, achieving a remarkable limit of 2.9 aM, thus addressing the intrinsic limitation of toehold switches in detecting low-abundance targets. The detection system's low cost, simplicity, and adaptability to various pathogens render it a valuable asset in the global health toolkit. This study presents a significant advancement in the field of synthetic biology, offering a robust, sensitive, and rapid diagnostic solution for Zika virus detection.

Dual-Enhanced SERS Satellite Immuno-Nanocomplex for Multiple PSA-Mediated PHI Assay Toward Clinical Prostate Cancer Screening

Prostate specific antigen (PSA) is widely used in liquid biopsy of prostate cancer (PCa) but still faces challenges due to the poor specificity. Herein, this study reports a double-SERS satellite immunoassay, made of an Au-Ag dealloyed intra-nanogap nanoflower (Au-Ag DINF) with strong SERS signals and Au magnetic nanoparticles (AuMNPs) with magnetic capture and SERS amplification, for sensing multiple PSA (free PSA (fPSA), complexed PSA (cPSA) and [-2]proPSA (p2PSA)) toward potential PCa screening. Unlike the previous studies focus on the tPSA and fPSA/tPSA ratio (f/t PSA%), this work introduces a multiple PSA-mediated Prostate Health Index (PHI) assay with significantly increased the predictive accuracy and specificity of PCa, especially the patients with a tPSA level in the "diagnostic gray zone". Practical analysis of clinical samples demonstrated the SERS immunoassay is capable of identifying the PCa subjects from healthy candidates (N = 13), and monitoring PCa patients before and after surgery (N = 5), as well as screening suspicious ones who are in the "gray zone" (N = 10). Overall, benefiting from the PSA-responsive satellite immuno-nanoassemble strategy, dual-SERS magnification effect, and multiple PSA-based PHI assessment, this proposes bioassay held enormous potential for the early diagnosis, screening, monitoring, and prognosis of PCa.

Enhanced Anti-Interference Photoelectrochemical DNA Bioassay: Grafting a Peptide-Conjugated Hairpin DNA Probe on a COF-Based Photocathode

Precise and sensitive analysis of specific DNA in actual human bodily fluids is crucial for the early diagnosis of major diseases and for a deeper understanding of DNA functions. Herein, by grafting a peptide-conjugated hairpin DNA probe to a covalent organic framework (COF)-based photocathode, a robust anti-interference photoelectrochemical (PEC) DNA bioassay was explored, which could specifically resist potential interference from nonspecific proteins and reducing species. Human immunodeficiency virus (HIV) DNA was used as the target DNA (tDNA) for the PEC DNA bioassay. The vinyl-functionalized COF (COF-V) was modified with meso-tetra(4-carboxyphenyl)-porphine (TCPP) and polydopamine (PDA) to fabricate a PDA/TCPP/COF-V photocathode, which served as the photocurrent signal transducer. Toward the unconventional recognition element, a hairpin DNA probe (hDNA) was efficiently linked with a linear zwitterionic peptide (LZP) to form the LZP-hDNA bioconjugate, which was then grafted onto the COF-based photocathode. The grafting of the LZP generated a sturdy anti-interference interface on the signal transducer. For tDNA probing, AgInS2 (AIS) quantum dots acted as signal quenchers, marked on signaling DNA (sDNA) to obtain AIS-sDNA labeling, and a striking drop in the photocurrent signal was achieved through λ-exonuclease (λ-Exo)-aided target recycling. This novel peptide-conjugated hairpin DNA probe endowed the PEC DNA bioassay with an impressive anti-interference property without requiring tedious steps. By combining the excellent photoelectric properties of the COF-based photocathode with an effective signaling strategy, accurate and sensitive results for tDNA probing were achieved.

Prussian blue-doped CaCO3 nanoparticle-labeled secondary antibodies for electrochemical immunoassay of interleukin-6 with migraine patients

The sensitive and accurate identification of interleukin-6 (IL-6) in biological fluids is essential for assessing migraine due to its role in different physiological and pathological processes. In this study, we designed a simple and feasible electrochemical immunosensing method for the voltammetric measurement of IL-6. The electrochemical immunosensor was fabricated through covalent conjugation of anti-IL-6 capture antibodies on the glassy carbon electrode with a typical carbodiimide coupling method. Anti-IL-6 secondary antibodies were labeled on the surface of Prussian blue-doped CaCO3 nanoparticles (PBCaNP) via the epoxy-amino reaction. The assay was carried out with a sandwich-type immunoreaction. In the presence of target IL-6, the analyte was sandwiched between the capture antibody and detection antibody. Thereafter, the carried PBCaNP accompanying the secondary antibody could be detected by using square wave voltammetry (SWV). The voltammetric peak current was dependent on the concentration of target IL-6. Under optimum conditions, the electrochemical immunosensor exhibited good analytical properties, and allowed detection of IL-6 within a wide linear range from 0.1 to 1000 pg mL-1. The limit of detection was estimated to be 0.078 pg mL-1 of IL-6 at the 3sB criterion. An intermediate reproducibility of ≤10.59% was accomplished with batch-to-batch identification, and good anti-interference capacity against other biomolecules was achieved. Importantly, clinical human serum samples obtained from 15 migraine patients were analyzed with the developed electrochemical immunosensors, giving results well-matched with those obtained from the referenced enzyme-linked immunosorbent assay (ELISA) method.

Enhanced photocurrents for photoelectrochemical immunoassay of alpha-fetoprotein with Pt-functionalized Bi2O2S nanoflowers

BACKGROUND

Designing heterojunctions with efficient electron-hole separation holds great promise for improving photoelectric response.

RESULTS

Herein, we reported a multifunctional Pt co-catalyst-modified Bi2O2S nanoflowers (BOS NFs) photocatalytic component for achieving an efficient photoelectric chemistry (PEC) immunosensor for alpha-fetoprotein (AFP). Briefly, the Pt co-catalyst improved the intrinsic band gap structure of BOS on the one hand, and on the other hand, it was able to achieve a rapid decomposition of hydrogen peroxide to hydroxyl radicals, which led to the improvement of electrochemical half-responses during the amplification of target immunosignals. In addition, Pt-functionalized BOS NFs (BOS-Pt) exhibited peroxidase-like enzymatic reaction activity and related properties. By enzyme-linked immunosorbent assay, a sandwich immuno-model in the presence of AFP catalyzed the production of hydrogen peroxide from the substrate glucose and the conversion of a sizable photoelectrochemical signal catalyzed by BOS-Pt. Following condition optimization, it was determined that the developed sensor exhibited a specific response to AFP over a wide linear range of 0.05-50 ng mL-1.

SIGNIFICANCE

This work provides a new strategy for developing efficient immunosensors from the perspective of modulating photoelectrochemical half-reactions.

Dual-electrode signal amplification self-powered biosensing platform based on nanozyme boosting target-induced DNA nanospace array for ultrasensitive detection of sugarcane Pokkah Boeng disease pathogenic bacteria

Sugarcane is a crop with significant economic importance worldwide. However, pokkah boeng disease poses a serious threat to its production and the sustainable development. There is a pressing necessity for precise and portable detection methods. We develop a dual-electrode signal amplification biosensing platform, for highly sensitive detection of sugarcane pokkah boeng disease pathogenic bacteria. This innovative platform integrates highly catalytic AuNPs/Mn3O4 nanozymes with N-GDY, along with a target-induced development of DNA nanostructure arrays. AuNPs/N-GDY serves as dual electrode substrates, and AuNPs/Mn3O4 nanozymes are surface-loaded as the bioanode. The biocathode is constructed by introducing DNA nanospace arrays onto the electrode through target-induced methods. [Ru(NH3)6]3+ is embedded into the nucleic acid double-helix scaffold via electrostatic adsorption, generating an EOCV signal that is strongly correlated with the target concentration. To further enhance sensitivity, the detection platform is combined with a capacitor to amplify the detection signal, utilizing its high power density, which results in a 22.5-fold increase in sensitivity. The method offers a linear detection range of 0.0001 to 10,000 pM and an detection limit of 32.5 aM (S/N = 3). This method supplies a novel approach for real-time monitoring and competent oversight of pokkah boeng disease pathogenic bacteria.

Simultaneous detection of multiple mycotoxins in agricultural products: Recent advances in optical and electrochemical sensing methods

Mycotoxin contamination poses serious threats to human and animal health. Food and environmental systems are often simultaneously contaminated with multiple mycotoxins, a problem that is further exacerbated by the synergistic toxicological effects of these co-occurring mycotoxins. Consequently, the development of rapid detection methods capable of simultaneously identifying multiple mycotoxins in agricultural products is essential to prevent their entry into the food chain. Compared to standard detection methods, optical and electrochemical (EC) sensing methods have distinct advantages for the rapid detection of mycotoxins. This review comprehensively summarizes the latest advancements in the field of simultaneous detection of multiple mycotoxins using optical and EC sensing methods over the last 6 years (2018-2024). First, the review introduces the classification and relevant principles of optical and EC sensing methods. Thereafter, it emphasizes innovative simultaneous detection strategies within these approaches. Finally, it discusses current challenges and offers a reference for further research. Currently, the main challenge lies in the mutual interference among targets, making the development of an interference-free detection platform essential. Furthermore, the ongoing development of integrated technology is expected to aid regulatory authorities in improving the quality of agricultural products for field applications.

X-ray/γ-ray/Ultrasound-Activated Persistent Luminescence Phosphors for Deep Tissue Bioimaging and Therapy

Persistent luminescence phosphors (PLPs) can remain luminescent after excitation ceases and have been widely explored in bioimaging and therapy since 2007. In bioimaging, PLPs can efficiently avoid tissue autofluorescence and light scattering interference by collecting persistent luminescence signals after the end of excitation. Outstanding signal-to-background ratios, high sensitivity, and resolution have been achieved in bioimaging with PLPs. In therapy, PLPs can continuously produce therapeutic molecules such as reactive oxygen species after removing excitation sources, which realizes sustained therapeutic activity after a single dose of light stimulation. However, most PLPs are activated by ultraviolet or visible light, which makes it difficult to reactivate the PLPs in vivo, particularly in deep tissues. In recent years, excitation sources with deep tissue penetration have been explored to activate PLPs, including X-ray, γ-ray, and ultrasound. Researchers found that various inorganic and organic PLPs can be activated by X-ray, γ-ray, and ultrasound, making these PLPs valuable in the imaging and therapy of deep-seated tumors. These X-ray/γ-ray/ultrasound-activated PLPs have not been systematically introduced in previous reviews. In this review, we summarize the recently developed inorganic and organic PLPs that can be activated by X-ray, γ-ray, and ultrasound to produce persistent luminescence. The biomedical applications of these PLPs in deep-tissue bioimaging and therapy are also discussed. This review can provide instructions for the design of PLPs with deep-tissue-renewable persistent luminescence and further promote the applications of PLPs in phototheranostics, noninvasive biosensing devices, and energy harvesting.

Unlocking Bright and Switchable Dimeric Singlet Oxygen Electrochemiluminescence by Surface Engineering

Visible electrochemiluminescence (ECL) of singlet oxygen (1O2) from the dimeric 1Δg state is a versatile and cost-efficient tool for sensing and imaging in various application fields such as biochemistry, pharmaceuticals, and material science. However, its implementation is hindered by weak emission and complex generation mechanisms. In this work, we enable a bright and switchable dimeric 1O2 ECL through facile yet effective surface engineering strategies on a screen-printed carbon electrode in aqueous media. Specifically, we complement a stepwise potential procedure with a pre-cathodic process to switch on the anodic 1O2 ECL and unravel how the in situ electrochemical pretreatments remarkably amplify the ECL intensity by modifying the surface oxygenates and promoting the 1O2-generating reactions. Additionally, ex situ oxygen plasma treatment on the electrode surface, which switches off the 1O2 ECL, further demonstrates the surface specificity of the 1O2 ECL from another perspective. Leveraging these surface strategies, we establish a sensing capability of the 1O2 ECL system with high sensitivity and selectivity toward tertiary amines. This work paves the way for translating a laboratory-scale 1O2-ECL system to portable and patternable sensing, imaging, and display applications.

Smartphone-Based Techniques Using Carbon Dot Nanomaterials for Food Safety Analysis

The development of portable and efficient nanoprobes to realize the quantitative/qualitative onsite determination of food pollutants is of immense importance for safeguarding human health and food safety. With the advent of the smartphone, the digital imaging property causes it to be an ideal diagnostic substrate to point-of-care analysis probes. Besides, merging the versatility of carbon dots nanostructures and bioreceptor abilities has opened an innovative assortment of construction blocks to design advanced nanoprobes or improving those existing ones. On this ground, massive endeavors have been made to combine mobile phones with smart nanomaterials to produce portable (bio)sensors in a reliable, low cost, rapid, and even facile-to-implement area with inadequate resources. Herein, this work outlines the latest advancement of carbon dots nanostructures on smartphone for onsite detecting of agri-food pollutants. Particularly, we afford a summary of numerous approaches applied for target molecule diagnosis (pesticides, mycotoxins, pathogens, antibiotics, and metal ions), for instance microscopic imaging, fluorescence, colorimetric, and electrochemical techniques. Authors tried to list those scaffolds that are well-recognized in complex media or those using novel constructions/techniques. Lastly, we also point out some challenges and appealing prospects related to the enhancement of high-efficiency smartphone based carbon dots systems.

Multi-Enzyme Cascade Nanoreactors for High-Throughput Immunoassay: Transitioning Concept in Lab to Application in Community

In this work, we reported a cholesterol oxidase (Chox)-loaded platinum (Pt) nanozyme with the collaborative cascade nanoreactor for the construction of nanozyme-enzyme-linked immunosorbent assay (N-ELSA) models to realize high-throughput rapid evaluation of cancer markers. Considering the high specific surface area and manipulable surface sites, ZIF-8 was used as a substrate for natural enzyme and nanozyme loading. The constructed ZIF-8-Pt nanozyme platform exhibited efficient enzyme-like catalytic efficiency with a standard corrected activity of 60.59 U mg-1, which was 12 times higher than that of the ZIF-8 precursor, and highly efficient photothermal conversion efficiency (∼35.49%). In N-ELISA testing, developed multienzyme photothermal probes were immobilized in microplates based on antigen-antibody-specific reactions. Cholesterol was reacted in a cascade to reactive oxygen radicals, which attacked 3,3',5,5'-tetramethylbenzidine, causing it to oxidize and color change, thus exhibiting highly enhanced efficient photothermal properties. Systematic temperature evaluations were performed by a hand-held microelectromechanical system thermal imager under the excitation of an 808 nm surface light source to determine the cancer antigen 15-3 (CA15-3) profiles in the samples. Encouragingly, the temperature signal from the microwells increased with increasing CA15-3, with a linear range of 2 mU mL-1 to 100 U mL-1, considering it to be the sensor with the widest working range for visualization and portability available. This work provides new horizons for the development of efficient multienzyme portable colorimetric-photothermal platforms to help advance the community-based process of early cancer detection.

Low-temperature subcritical water dechlorination composites of waste PVC/coal fly ash with powerful sensing activity for chemiluminescent detection of acetamiprid and imidacloprid

Pesticide residues in agricultural products are serious threat to people's health. Real-time monitoring of pesticides residues in the environment and agricultural products posed challenges to sustainable methods with high analytical performance for pesticide detection. Herein, waste PVC/coal fly ash (the mass ratio of PVC and coal fly ash was 4:1) was dechlorinated in subcritical water at low temperature to achieve nearly 100 % dechlorination of PVC and obtain carbon-based composite materials (CM-Fe/Al/Si-dPVC) with strong sening activity. For CM-Fe/Al/Si-dPVC, CFe bonding resulted in strong electron migration, and nano/μm SiO2 and Al2O3 doping in the layered polyene C matrix provided large specific surface area, and silicon hydroxyl created good heterogeneous catalytic interfaces. CM-Fe/Al/Si-dPVC could strongly trigger luminol chemiluminescence (CL) reaction and produce intense CL signals. Neonicotinoid pesticides (acetamiprid and imidacloprid) bonded with CM-Fe/Al/Si-dPVC through coordination chelation and hydrogen bonding, which shielded the catalytic active site and increased the Fermi level of system, thus quenching CL reaction. Inspired by these, a cheap CL assay was constructed for detecting neonicotinoids combinations of acetamiprid and imidacloprid (NICs). The detection limits of NICs were 0.7 ng/L. Satisfactory recoveries were obtained for real agricultural products and environmental samples. The results of life cycle evaluation (LCA) revealed that the strategy had significantly small global warming potential (GWP). This work presented a sustainable method with environmental benefits for the detection of neonicotinoids, and also opened up new way for the recycling of organic solid wastes.

Smartphone-Based Free-to-Total Prostate Specific Antigen Ratio Detection System Using a Colorimetric Reaction Integrated with Proximity-Induced Bio-Barcode and CRISPR/Cas12a Assay

The free-to-total prostate-specific antigen (f/t-PSA) ratio is of great significance in the accurate diagnosis of prostate cancer. Herein, a smartphone-based detection system is reported using a colorimetric reaction integrated with proximity-induced bio-barcode and the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas12a assay for f/t-PSA ratio detection. DNA/antibody recognition probes are designed to bind f-PSA or t-PSA and induce the release of the DNA bio-barcode. The CRISPR/Cas12a system is activated by the DNA bio-barcode to release Ag+ from the C-Ag+-C structure of the hairpin DNA. The released Ag+ is used to affect the tetramethylbenzidine (TMB)-H2O2-based colorimetric reaction catalyzed by Pt nanoparticles (NPs), as the peroxidase-like activity of the Pt NPs can be efficiently inhibited by Ag+. A smartphone with a self-developed app is used as an image reader and analyzer to analyze the colorimetric reaction and provide the results. A limit of detection of 0.06 and 0.04 ng mL-1 is achieved for t-PSA and f-PSA, respectively. The smartphone-based method showed a linear response between 0.1 and 100 ng mL-1 of t-PSA or f-PSA. In tests with clinical samples, the smartphone-based method successfully diagnosed prostate cancer patients from benign prostatic hyperplasia patients and healthy cases with high sensitivity and specificity.

Increasing the sensitivity and accuracy of detecting exosomes as biomarkers for cancer monitoring using optical nanobiosensors

The advancement of nanoscience and material design in recent times has facilitated the creation of point-of-care devices for cancer diagnosis and biomolecule sensing. Exosomes (EXOs) facilitate the transfer of bioactive molecules between cancer cells and diverse cells in the local and distant microenvironments, thereby contributing to cancer progression and metastasis. Specifically, EXOs derived from cancer are likely to function as biomarkers for early cancer detection due to the genetic or signaling alterations they transport as payload within the cancer cells of origin. It has been verified that EXOs circulate steadily in bodily secretions and contain a variety of information that indicates the progression of the tumor. However, acquiring molecular information and interactions regarding EXOs has presented significant technical challenges due to their nanoscale nature and high heterogeneity. Colorimetry, surface plasmon resonance (SPR), fluorescence, and Raman scattering are examples of optical techniques utilized to quantify cancer exosomal biomarkers, including lipids, proteins, RNA, and DNA. Many optically active nanoparticles (NPs), predominantly carbon-based, inorganic, organic, and composite-based nanomaterials, have been employed in biosensing technology. The exceptional physical properties exhibited by nanomaterials, including carbon NPs, noble metal NPs, and magnetic NPs, have facilitated significant progress in the development of optical nanobiosensors intended for the detection of EXOs originating from tumors. Following a summary of the biogenesis, biological functions, and biomarker value of known EXOs, this article provides an update on the detection methodologies currently under investigation. In conclusion, we propose some potential enhancements to optical biosensors utilized in detecting EXO, utilizing various NP materials such as silicon NPs, graphene oxide (GO), metal NPs, and quantum dots (QDs).

Portable photoelectrochemical immunoassay with micro-electro-mechanical-system for alpha-fetoprotein in hepatocellular carcinoma

Early detection of cancer has a profound impact on patient survival and treatment outcomes considering high treatment success rates and reduced treatment complexity. Here, we developed a portable photoelectrochemical (PEC) immune platform for sensitive testing of alpha-fetoprotein (AFP) based on Pt nanocluster (Pt NCs) loaded defective-state g-C3N4 photon-electron transducers. The broad forbidden band structure of g-C3N4 was optimized by the nitrogen doping strategy and additional homogeneous porous structure was introduced to further enhance the photon utilization. In addition, the in-situ growth of Pt NCs provided efficient electron transfer catalytic sites for sacrificial agents, which were used to further improve the sensitivity of the sensor. Efficient photoelectric conversion under a hand-held flashlight was determined by the geometry of the transducer and the energy band design, and the portable design of the PEC sensor was realized. The developed sensing platform exhibited a wide linear response range (0.1-50 ng mL-1) and low limit of detection (0.043 ng mL-1) for AFP under optimum conditions. This work provides a new idea for designing portable PEC biosensing platforms to meet the current mainstream POC testing needs.

Functional Green-Emitting Mn2+-doped Zinc Germanate Persistent Luminescent Nanoparticles for Dual-Mode Immunochromatographic Detection

Immunochromatography is a commonly used immediate detection technique, using signal labels to generate detection signals for rapid medical diagnosis. However, its detection sensitivity is affected by background fluorescence caused by the excitation light source. We have developed an immunochromatographic test strip using Zn2GeO4:Mn2+ (ZGM) persistent luminescent nanoparticles (PLNPs) for immediate fluorescence detection and highly sensitive persistent luminescence (PersL) detection without background fluorescence interference. ZGM emits a strong green light when exposed to ultraviolet (UV) excitation, and its green PersL can persist for over 30 min after the excitation light is turned off. We modified the surface of ZGM with heparin-binding protein (HBP) antibodies to create immunochromatographic test strips for the detection of HBP as the target analyte. Under UV excitation, the chromatography test paper can be visually observed at concentrations as low as 25 ng/mL. After the excitation light source is switched off, PersL can achieve a detection limit of 4.7 ng/mL without background interference. This dual-mode immunochromatographic detection, based on ZGM, shows great potential for in vitro diagnostic applications.

Plasmonic silver and gold nanoparticles: shape- and structure-modulated plasmonic functionality for point-of-caring sensing, bio-imaging and medical therapy

Silver and gold nanoparticles have found extensive biomedical applications due to their strong localized surface plasmon resonance (LSPR) and intriguing plasmonic properties. This review article focuses on the correlation among particle geometry, plasmon properties and biomedical applications. It discusses how particle shape and size are tailored via controllable synthetic approaches, and how plasmonic properties are tuned by particle shape and size, which are embodied by nanospheres, nanorods, nanocubes, nanocages, nanostars and core-shell composites. This article summarizes the design strategies for the use of silver and gold nanoparticles in plasmon-enhanced fluorescence, surface-enhanced Raman scattering (SERS), electroluminescence, and photoelectrochemistry. It especially discusses how to use plasmonic nanoparticles to construct optical probes including colorimetric, SERS and plasmonic fluorescence probes (labels/reporters). It also demonstrates the employment of Ag and Au nanoparticles in polymer- and paper-based microfluidic devices for point-of-care testing (POCT). In addition, this article highlights how to utilize plasmonic nanoparticles for in vitro and in vivo bio-imaging based on SERS, fluorescence, photoacoustic and dark-field models. Finally, this article shows perspectives in plasmon-enhanced photothermal and photodynamic therapy.

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.

Constructed MXene matrix composites as sensing material and applications thereof: A review

Most studies on MXene matrix composites for sensor development have primarily focused on synthesis and application. Nevertheless, there is currently a lack of research on how the introduction of different materials affects the sensing properties of these composites. The rapid development of MXene has raised intriguing questions about improving sensor performance by combining MXene with other materials such as polymers, metals and inorganic non-metals. This review will concentrate on the construction of MXene-based composites and explore ways to enhance their sensor applications. Specifically, this review describes why the introduction of materials to the system brings the advantage of low concentration and high sensitivity assays, as well as the MXene-based frameworks that have been recently investigated. Lastly, in order to capture the current trend of MXene-based composites in sensor applications and identify promising research directions, this review will critically evaluate the potential applications of newly developed MXene systems.

Bioluminescence assay for rapid detection of live Staphylococcus aureus based on the enrichment of egg yolk antibody modified magnetic metal organic framework immunobeads

Specific and rapid detection of live Staphylococcus aureus (S.A) in environmental and food samples is critically important for protecting human health. In order to fulfill this purpose, two kinds of novel egg yolk antibody (IgY) immobilized immunomagnetic beads (IMBs; mSiO2-IgY and mMOF-IgY), with core-shell mSiO2 and mMOF as substrate, were prepared for selectively enriching S.A from samples. Furthermore, the IMBs with captured S.A were collected and re-dissolved in 0.5 mL PBS. After that, a cotton swab coated with sodium dodecylsulfate (SDS) was put in the solution to lyse S.A cells and emit ATP bioluminescence of the luciferin/luciferase system. Finally, a portable bioluminescence detector was used for quantification of ATP corresponding to S.A concentration. The results demonstrated that mMOF-IgY can enrich more S.A than mSiO2-IgY and emit a stronger signal. The reasons may be due to the higher immobilization amount of IgY on the IMBs. Under optimal conditions, the calibration line of S.A concentration was 10-105 CFU mL-1 by mMOF-IgY within 30 min. The low detection limit of S.A was 3 CFU mL-1. The results demonstrated that the assay takes much shorter time than plate counting. Its portability and excellent detection capability are suitable for rapid monitoring of specific pathogens in foods.

A paper-based photoelectrochemical aptsensor using near-infrared light-responsive AgBiS2 nanoflowers as probes for the detection of Staphylococcus aureus in pork

Staphylococcus aureus is a gram-positive bacterium that can easily cause outbreaks of food-borne diseases. In this work, a signal-enhanced three-dimensional paper-based photoelectrochemical (PEC) aptsensor for the rapid and sensitive determination of S. aureus was developed. Specifically, gold nanoparticles (AuNPs) were electrodeposited on a paper-based working electrode to provide binding sites for a sulfhydryl-functionalized aptamer. Subsequently, S. aureus was captured with high specificity by a carboxyl-functionalized aptamer modified with amino-functionalized AgBiS2 nanoflowers (NH2-AgBiS2 NFs), which functionalized as PEC probes that generated strong photocurrent under irradiation with 980-nm light. By exploiting the "aptamer-target-aptamer" PEC sensing platform, the rapid and ultrasensitive detection of S. aureus was achieved. The sensor had a wide linear range of 20 to 2 × 107 CFU/mL and low limit of detection of 4 CFU/mL. Further, the applicability of the as-prepared aptsensor was successfully certified for the analysis of pork samples artificially contaminated with S. aureus.

NLISA versus enzyme-linked immunosorbent assay: Nanozyme-linked immunosorbent array based on platinum sub-nanocluster nanozyme for α-fetoprotein detection

Rapid and accurate identification of tumor metabolic markers is important for early tumor diagnosis and individualized treatment. Here, a stable monodisperse sub-nanometer platinum (Pt) material was developed as a highly efficient nanozyme with a specific activity of peroxidase as high as 20.86 U mg-1 through the growth of in situ domain-limited Pt quantum dots via the polymer polyvinylpyrrolidone. Further, the synthesis of large quantities of Pt-loaded SiO2 (Pt-SiO2 ) was determined by silylation reaction and used for naked eye colorimetric testing of human alpha-fetoprotein (AFP). In particular, the immunization incubation process occurred in preprepared microplates. A nanozyme-based immunomodel was constructed in the presence of the target AFP, and a chromogenic reaction occurred with exogenous hydrogen peroxide and the chromogenic substrate tetramethylbenzidine. On optimization of experimental conditions, the dynamic working response range for AFP was found to be 0.05-20 ng mL-1 , with a limit of detection of 38.7 pg mL-1 . This work provides a new strategy to design efficient nanozyme-based enzyme-linked immunochromatographic platforms to meet the practical use of replacing natural enzymes.

Tungsten-based polyoxometalate nanoclusters with remarkable reactive oxygen species-scavenging activity efficiently quenched luminol-based electrochemiluminescence for sensitive detection of Her-2

This study aimed to develop a quenching-type electrochemiluminescence (ECL) immunosensor for human epidermal growth factor receptor (Her-2) detection. Firstly, Pd/NiFeOx nanoflowers decorated by in situ formation of gold nanoparticles (Au NPs) and 2D Ti3C2 MXene nanosheets were synthesized (AuPd/NiFeOx/Ti3C2) as carriers to load luminol and primary antibodies. Impressively, AuPd/NiFeOx/Ti3C2 with excellent peroxidase-like activity could accelerate the decomposition of the coreactant H2O2 generating more reactive oxygen species (ROSs) under the working potential from 0 to 0.8 V, resulting in highly efficient ECL emission at 435-nm wavelengths. The introduction of tungsten-based polyoxometalate nanoclusters (W-POM NCs) which exhibit remarkable ROSs-scavenging activity as secondary antibody labels could improve the sensitivity of immunosensors. The ZnO nanoflowers were employed to encapsulate minute-sized W-POM NCs, and polydopamine was self-polymerized on the surface of Zn(W-POM)O to anchor secondary antibodies. The mechanism of the quenching strategy was explored and it was found that W-POM NCs could consume ROSs by the redox reaction of W5+ resulting in W6+. The proposed ECL immunosensor displayed a wide linear response range of 0.1 pg·mL-1 to 50 ng·mL-1, and a low detection limit of 0.036 pg mL-1 (S/N = 3). The recoveries ranged from 93.9 to 99.4%, and the relative standard deviation (RSD) was lower than 10%. This finding is promising for the design of detecting new protein biomarkers.

Fabrication of near infrared light responsive photoelectrochemical immunosensor for in vivo detection of melanoma cells

Effective and convenient detection of melanoma cells with high sensitivity is essential to identify malignant melanoma in its early stage. However, the existing detection methods, such as immunohistochemical analysis, are too complicated and time-consuming to realize the convenient in vivo and in situ detection. Herein, a near infrared responsive photoelectrochemical (PEC) immunosensor is proposed with plasmonic Au nanoparticles-photonic TiO2 nanocaves (Au/TiO2 NCs) as photon harvest and conversion transducer and antibody as cell recognition unit. The micro-antibody/Au/TiO2 NCs photoelectrode can easily in vivo distinguish melanoma cells and can realize sensitive detection of melanoma cells in short time of 1 min with a lowest limit of detection of 2 cell mL-1. The PEC immunosensor strategy not only allows us to pioneeringly implement sensitive in vivo bio-detection, but also opens up a new avenue for rational design of cell recognition units and micro-electrode for universal and reliable bio-detections.

Enhanced NIR-II Fluorescent Lateral Flow Biosensing Platform Based on Supramolecular Host-Guest Self-Assembly for Point-of-Care Testing of Tumor Biomarkers

Point-of-care detection of tumor biomarkers with high sensitivity remains an enormous challenge in the early diagnosis and mass screening of cancer. Fluorescent lateral flow immunoassay (LFA) is an attractive platform for point-of-care testing due to its inherent advantages. Particularly, a fluorescent probe is crucial to improving the analytical performance of the LFA platform. Herein, we developed an enhanced second near-infrared (NIR-II) LFA (ENIR-II LFA) platform based on supramolecular host-guest self-assembly for detection of the prostate-specific antigen (PSA) as a model analyte. In this platform, depending on the effective supramolecular surface modification strategy, cucurbit[7]uril (CB[7])-covered rare-earth nanoparticles (RENPs) emitting in the NIR-II (1000-1700 nm) window were prepared and employed as an efficient fluorescent probe (RENPs-CB[7]). Benefiting from its superior optical properties, such as low autofluorescence, excellent photostability, enhanced fluorescence intensity, and increased antibody-conjugation efficiency, the ENIR-II LFA platform displayed a wide linear detection range from 0.65 to 120 ng mL-1, and the limit of detection was down to 0.22 ng mL-1 for PSA, which was 18.2 times lower than the clinical cutoff value. Moreover, the testing time was also shortened to 6 min. Compared with the commercial visible fluorescence LFA kit (VIS LFA) and the previously reported NIR-II LFA based on a RENPs-PAA probe, this ENIR-II LFA demonstrated more competitive advantages in analytical sensitivity, detection range, testing time, and production cost. Overall, the ENIR-II LFA platform offers great potential for the highly sensitive, rapid, and convenient detection of tumor biomarkers and is expected to serve as a useful technique in the general population screening of the high-incidence cancer region.

Development of a highly sensitive immunoassay based on pentameric nanobodies for carcinoembryonic antigen detection

BACKGROUND

Carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM-5) is a well-characterized biomarker for the clinical diagnosis of various cancers. Nanobodies, considered the smallest antibody fragments with intact antigen-binding capacity, have gained significant attention in disease diagnosis and therapy. Due to their peculiar properties, nanobodies have become promising alternative diagnostic reagents in immunoassay. However, nanobodies-based immunoassay is still hindered by small molecular size and low antigen capture efficacy. Therefore, there is a pressing need to develop novel nanobody-based immunoassays with superior performance.

RESULTS

A novel pentameric nanobodies-based immunoassay (PNIA) was developed with enhanced sensitivity and specificity for CEACAM-5 detection. The binding epitopes of three anti-CEACAM-5 nanobodies (Nb1, Nb2 and Nb3) were analyzed. To enhance the capture and detection efficacy of CEACAM-5 in the immunoassay, we engineered bispecific nanobodies (Nb1-Nb2-rFc) as the capture antibody, and developed the FITC-labeled pentameric nanobodies (Nb3-VT1B) as the detection antibody. The binding affinities of Nb1-Nb2-rFc (1.746 × 10-10) and Nb3-VT1B (1.279 × 10-11) were significantly higher than those of unmodified nanobodies (Nb1-rFc, 4.063 × 10-9; Nb2-rFc, 2.136 × 10-8; Nb3, 3.357 × 10-9). The PNIA showed a linear range of 0.625-160 ng mL-1 with a correlation coefficient R2 of 0.9985, and a limit of detection of 0.52 ng mL-1, which was 24-fold lower than the immunoassay using monomeric nanobody. The PNIA was validated with the spiked human serum. The average recoveries ranged from 91.8% to 102% and the coefficients of variation ranged from 0.026% to 0.082%.

SIGNIFICANCE AND NOVELTY

The advantages of nanobodies offer a promising alternative to conventional antibodies in disease diagnosis. The novel PNIA demonstrated superior sensitivity and high specificity for the detection of CEACAM-5 antigen. This bispecific or multivalent nanobody design will provide some new insights into the design of immunoassays for clinical diagnosis.

Ultrasensitive detection of miRNA-21 by click chemistry and fluorescein-mediated photo-ATRP signal amplification

The development of a convenient and efficient assay using miRNA-21 as a lung cancer marker is of great importance for the early prevention of cancer. Herein, an electrochemical biosensor for the detection of miRNA-21 was successfully fabricated under blue light excitation using click chemistry and photocatalytic atom transfer radical polymerization (photo-ATRP). By using hairpin DNA as a recognition probe, the electrochemical sensor deposits numerous electroactive monomers (ferrocenylmethyl methacrylate) on the electrode surface under the reaction of photocatalyst (fluorescein) and pentamethyldiethylenetriamine, thereby achieving signal amplification. This biosensor is sensitive, precise and selective for miRNA-21, and is highly specific for RNAs with different base mismatches. Under optimal conditions, the biosensor showed a linear relationship in the range of 10 fM ∼1 nM (R2 = 0.995), with a detection limit of 1.35 fM. Furthermore, the biosensor exhibits anti-interference performance when analyzing RNAs in serum samples. The biosensor is based on green chemistry and has the advantages of low cost, specificity and anti-interference ability, providing economic benefits while achieving detection objectives, which makes it highly promising for the analysis of complex samples.

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

In this paper, a photoelectrochemical (PEC)-surface-enhanced Raman scattering (SERS) dual-mode biosensor is constructed coupled with a dual-recognition binding-induced DNA walker with a carbon nitride nanosheet (C3N4)/MXene-gold nanoparticles (C/M-Au NPs) accelerator, which is reliable and capable for sensitive and accurate detection of Staphylococcus aureus (S. aureus). Initially, a photoactive heterostructure is formed by combining C3N4 and MXene via a simple electrostatic self-assembly as they possess well-matched band-edge energy levels. Subsequently, in situ growth of gold nanoparticles on the formed surface results in better PEC performance and SERS activity, because of the synergistic effects of surface plasmon resonance and Schottky barrier. Furthermore, a three-dimensional, bipedal, and dual-recognition binding-induced DNA walker is introduced with the formation of Pb2+-dependent DNAzyme. In the presence of S. aureus, a significant quantity of intermediate DNA (I-DNA) is generated, which can open the hairpin structure of Methylene Blue-tagged hairpin DNA (H-MB) on the electrode surface, thereby enabling the switch of signals for the quantitative determination of S. aureus. The constructed PEC-SERS dual-mode biosensor that can be mutually verified under one reaction effectively addresses the problem of the low detection accuracy of traditional sensors. Experimental results revealed that the effective combination of PEC and SERS is achieved for amplification detection of S. aureus with a detection range of 5-108 CFU/mL (PEC) and 10-108 CFU/mL (SERS), and a detection of limit of 0.70 CFU/mL (PEC) and 1.35 CFU/mL (SERS), respectively. Therefore, this study offers a novel and effective dual-mode sensing strategy, which has important implications for bioanalysis and health monitoring.

Inspired by game theory: Multi-signal output photoelectrochemical point-of-care immunoassay based on target-triggered organic electronic barriers

This work presents an integrated photoelectrochemical, impedance and colorimetric biosensing platform for flexible detection of cancer markers based on the targeted response by combining liposome amplification strategies and target-induced non-in situ formation of electronic barriers as the signal transduction modality on carbon-modified CdS photoanodes. Inspired by game theory, the carbon layer modified CdS hyperbranched structure with low impedance and high photocurrent response was firstly obtained by surface modification of CdS nanomaterials. Through a liposome-mediated enzymatic reaction amplification strategy, a large number of organic electron barriers were formed by a biocatalytic precipitation (BCP) reaction triggered by horseradish peroxidase released from cleaved liposomes after the introduction of the target molecule, thereby increasing the impedance characteristics of the photoanode as well as attenuating the photocurrent. The BCP reaction in the microplate was accompanied by a significant color change, which opened up a new window for point-of-care testing. Taking carcinoembryonic antigen (CEA) as a proof of concept, the multi-signal output sensing platform showed a satisfactory sensitive response to CEA with an optimal linear range of 20 pg mL^-1-100 ng mL^-1. The detection limit was as low as 8.4 pg mL^-1. Meanwhile, with the assistance of a portable smartphone and a miniature electrochemical workstation, the electrical signal obtained was synchronized with the colorimetric signal to correct the actual target concentration in the sample, further reducing the occurrence of false reports. Importantly, this protocol provides a new idea for the sensitive detection of cancer markers and the construction of a multi-signal output platform.

Development and performance evaluations of an HER-2 kit

Objective To develop a kit for detecting human epidermal growth factor receptor 2 (HER-2) in the human body. Methods The HER-2 kit was evaluated based on an automated magnetic particle chemiluminescence platform. The kit was developed using the double antibody sandwich-complexation method. Results The kit showed a linear range of 0.01-800 ng/mL, with a linear R2 of >0.999. The limit of the blank was 0.0039 ng/mL, and the precision at 1.00 ng/mL was 9.4%. The recovery rate at 10.00 ng/mL was 97.81-101.81%. The negative serum reference range was 0-8.23 ng/mL. Conclusions The kit had a wide linear range, high accuracy, good precision, and high sensitivity, indicating that it has good application prospects.

Photoinduced Electron Transfer Modulated Photoelectric Signal: Toward an Organic Small Molecule-Based Photoelectrochemical Platform for Formaldehyde Detection

Photoelectrochemical (PEC) sensing has been rapidly evolving in recent years, while the introduction of small molecules with specific recognition functions into the sensing interface remains a nascent area of study. In this work, we reported a PEC biosensor for formaldehyde (FA) detection based on photoinduced electron transfer (PET)-gated electron injection between organic small molecules and inorganic semiconducting substrates. Specifically, an FA-responsive probe (NA-FA-COOH) and TiO2 nanoarrays were integrated to construct a PEC platform (NFC/TiO2) via a coordination bond. NFC served simultaneously as a target-specific recognition element and a modulator of photoinduced electron injection. Treatment of NFC/TiO2 by FA would suppress the intramolecular PET process, with the quenched photocurrent signal due to the changed carrier transfer pathway, thus establishing the PEC platform for FA based on effective PET modulation. The proposed PEC system exhibited high selectivity and sensitivity, with a low detection limit of 0.071 μM. This study presents a novel perspective on the use of organic small molecules with a PET effect for advanced PEC bioanalysis.

Enzyme‐Encapsulated Protein Trap Engineered Metal–Organic Framework‐Derived Biomineral Probes for Non‐Invasive Prostate Cancer Surveillance

A paper‐based naked‐eye recognition assay with enzyme‐encapsulated protein engineered metal–organic framework‐derived biominerals is developed for direct quantification of sarcosine in urine samples for screening of prostate cancer individuals. The detection strategy stems from the successful construction of a cascade response model, which involves the introduction of a cascade enzymatic catalytic reaction on Pt nanoparticles (NPs)‐loaded porous CeO2 by integrating a sarcosine oxidase as a special recognition unit and a chromogenic substrate as a signal molecule reporter. Pt NPs‐loaded CeO2 is subjected to a one‐step thermal treatment based on multilayered mesoporous Ce‐based metal–organic framework, and the calcined CeO2 exhibits the same distinct porous graded structure. Importantly, introduction of Pt NPs sharply enhances the peroxidase‐like activity of CeO2, which is considered to be caused by the difference in the adsorption behavior of hydrogen peroxide on the CeO2 surface and Pt/CeO2 obtained by density functional theory calculations. On the basis of this, the probe is used on a mass‐producible paper‐based working platform and 3D‐printed device to specifically screen for minor differences in sarcosine between urine samples from cancer patients and normal individuals. Enzyme‐assisted cascade catalytic reaction can be extended by replacing different recognition units for multiple analytes.

Photoelectrochemical sensors based on paper and their emerging applications in point-of-care testing

Point-of-care testing (POCT) technology is urgently required owing to the prevalence of the Internet of Things and portable electronics. In light of the attractive properties of low background and high sensitivity caused by the complete separation of excitation source and detection signal, the paper-based photoelectrochemical (PEC) sensors, featured with fast in analysis, disposable and environmental-friendly have become one of the most promising strategies in POCT. Therefore, in this review, the latest advances and principal issues in the design and fabrication of portable paper-based PEC sensors for POCT are systematically discussed. Primarily, the flexible electronic devices that can be constructed by paper and the reasons why they can be used in PEC sensors are expounded. Afterwards, the photosensitive materials involved in paper-based PEC sensor and the signal amplification strategies are emphatically introduced. Subsequently, the application of paper-based PEC sensors in medical diagnosis, environmental monitoring and food safety are further discussed. Finally, the main opportunities and challenges of paper-based PEC sensing platforms for POCT are briefly summarized. It provides a distinct perspective for researchers to construct paper-based PEC sensors with portable and cost-effective, hoping to enlighten the fast development of POCT soon after, as well as benefit human society.

Enzyme-catalyzed high-performing reaction with in-situ amplified photocurrent on carbon-functionalized inorganic photoanode for immunosensing

An enzyme-catalyzed high-performing reaction with in-situ amplified photocurrent was innovatively designed for the quantitative screening of carcinoembryonic antigen (CEA) in biological fluids by coupling with carbon-functionalized inorganic photoanode. A split-type photoelectrochemical (PEC) immunoassay was initially executed with horseradish peroxidase (HRP)-labeled secondary antibody on the capture antibody-coated microtiter. Then, the photocurrent of carbon-functionalized inorganic photoanode were improved through enzymatic insoluble product. Experimental results revealed that introduction of the outer carbon layer on the inorganic photoactive materials caused the amplifying photocurrent because of the improving light harvesting and separation of photo-generated e^-/h⁺ pairs. Under optimum conditions, the split-type photoelectrochemical immunosensing platform displayed good photocurrent responses within the dynamic range of 0.01 - 80 ng mL^-1 CEA, and allowed the detection of CEA as low as a concentration of 3.6 pg mL^-1 at the 3S_blank level. The strong attachment of antibodies onto nano label and high-performing photoanode resulted in a good repeatability and intermediate precision down to 9.83%. No significant differences at the 0.05 significance level were encountered in the analysis of six human serum specimens between the developed PEC immunoassay and the commercially available CEA ELISA kits.

Determination of acetic acid in enzymes based on the cataluminescence activity of graphene oxide-supported carbon nanotubes coated with NiMn layered double hydroxides

A cataluminescence (CTL) method has been developed for the rapid determination of acetic acid in enzyme products. The NiMn LDH/CNT/GO was synthesized based on the nanohybridization of NiMn layered double hydroxide (NiMn LDH), carbon nanotubes (CNTs), and graphene oxide (GO). The composite has excellent CTL activity against acetic acid. It could be ascribed to the larger specific surface area and more exposure to active sites. NiMn LDH/CNT/GO is used as a catalyst in the CTL method based on its special structure and advantages. There is a linear relationship between CTL response and the acetic acid concentration in the range 0.31-12.00 mg·L^-1 with the detection limit of 0.10 mg·L^-1. The developed method is rapid and takes only about 13 s. The method is applied to the determination of acetic acid in enzyme samples with little sample preparation. The result of the CTL method shows good agreement with that of the gas chromatography method. The proposed CTL method possesses promising potential in the quality monitoring of enzymes.

Insights into the multirole CoAl layered double hydroxide on boosting photoelectrochemical activity of hematite: Application to hydrogen peroxide sensing

As an important compound in many industrial and biological processes, hydrogen peroxide (H₂O₂) would cause harmfulness to human health at high concentration level. It thus is urgent to develop highly sensitive and selective sensors for practical H₂O₂ detection in the fields of water monitoring, food quality control, and so on. In this work, CoAl layered double hydroxide ultrathin nanosheets decorated hematite (CoAl-LDH/α-Fe₂O₃) photoelectrode was successfully fabricated by a facile hydrothermal process. CoAl-LDH/α-Fe₂O₃ displays the relatively wide linear range from 1 to 2000 μM with a high sensitivity of 132.0 μA mM^-1 cm^-2 and a low detection limit of 0.04 μM (S/N ≥ 3) for PEC detection of H₂O₂, which is superior to other similar α-Fe₂O₃-based sensors in literatures. The (photo)electrochemical characterizations, such as electrochemical impedance spectroscopy, Mott-Schottky plot, cyclic voltammetry, open circuit potential and intensity modulated photocurrent spectroscopy, were used to investigate the roles of CoAl-LDH on the improved PEC response of α-Fe₂O₃ toward H₂O₂. It revealed that, CoAl-LDH could not only passivate the surface states and enlarge the band bending of α-Fe₂O₃, but also could act as trapping centers for holes and followed by as active sites for H₂O₂ oxidation, thus facilitated the charge separation and transfer. The strategy for boosting PEC response would be help for the further development of semiconductor-based PEC sensors.

Real-Time Biosensing Bacteria and Virus with Quartz Crystal Microbalance: Recent Advances, Opportunities, and Challenges

Continuous monitoring of pathogens finds applications in environmental, medical, and food industry settings. Quartz crystal microbalance (QCM) is one of the promising methods for real-time detection of bacteria and viruses. QCM is a technology that utilizes piezoelectric principles to measure mass and is commonly used in detecting the mass of chemicals adhering to a surface. Due to its high sensitivity and rapid detection times, QCM biosensors have attracted considerable attention as a potential method for detecting infections early and tracking the course of diseases, making it a promising tool for global public health professionals in the fight against infectious diseases. This review first provides an overview of the QCM biosensing method, including its principle of operation, various recognition elements used in biosensor creation, and its limitations and then summarizes notable examples of QCM biosensors for pathogens, focusing on microfluidic magnetic separation techniques as a promising tool in the pretreatment of samples. The review explores the use of QCM sensors in detecting pathogens in various samples, such as food, wastewater, and biological samples. The review also discusses the use of magnetic nanoparticles for sample preparation in QCM biosensors and their integration into microfluidic devices for automated detection of pathogens and highlights the importance of accurate and sensitive detection methods for early diagnosis of infections and the need for point-of-care approaches to simplify and reduce the cost of operation.

Fluorescence-Enhanced Microfluidic Biosensor Platform Based on Magnetic Beads with Highly Stable ZnO Nanorods for Biomarker Detection

Existing affinity-based fluorescence biosensing systems for monitoring of biomarkers often utilize a fixed solid substrate immobilized with capture probes limiting their use in continuous or intermittent biomarker detection. Furthermore, there have been challenges of integrating fluorescence biosensors with a microfluidic chip and low-cost fluorescence detector. Herein, we demonstrated a highly efficient and movable fluorescence-enhanced affinity-based fluorescence biosensing platform that can overcome the current limitations by combining fluorescence enhancement and digital imaging. Fluorescence-enhanced movable magnetic beads (MBs) decorated with zinc oxide nanorods (MB-ZnO NRs) were used for digital fluorescence-imaging-based aptasensing of biomolecules with improved signal-to-noise ratio. High stability and homogeneous dispersion of photostable MB-ZnO NRs were obtained by grafting bilayered silanes onto the ZnO NRs. The ZnO NRs formed on MB significantly improved the fluorescence signal up to 2.35 times compared to the MB without ZnO NRs. Moreover, the integration of a microfluidic device for flow-based biosensing enabled continuous measurements of biomarkers in an electrolytic environment. The results showed that highly stable fluorescence-enhanced MB-ZnO NRs integrated with a microfluidic platform have significant potential for diagnostics, biological assays, and continuous or intermittent biomonitoring.

Dual-sensitized heterojunction PDA/ZnO@MoS2 QDs combined with multilocus domino-like DNA cascade reaction for ultrasensitive photoelectrochemical biosensor

In this work, by integrating with a highly efficient multilocus domino-like cascade reaction on DNA nanonet, an ultrasensitive PEC biosensor based on dual-sensitized PDA/ZnO@MoS₂ QDs photoactive material as signal probe was proposed for detection of miRNA-182-5p. The dual-sensitized PDA/ZnO@MoS₂ QD composed by both of p-n and S-scheme heterojunctions on electrode generated an extremely high initial PEC signal, which however quenched by CdTe QDs decorated on DNA nanonet owing to the significant p-n quenching effect. Thereafter, the output DNA (RS) from DSN enzyme-assisted target recycling amplification triggered an ingenious multilocus domino-like DNA cascade reaction on DNA nanonet for releasing numerous CdTe QDs. Thanks to the multilocus domino-like mode that owned abundant binding sites for increasing trigger efficiency and drove cascade reaction automatically advance along four stated pathways, the target conversion rate could be improved effectively compared with that of traditional approaches, significantly enhancing the detection sensitivity. Consequently, the developed PEC biosensor exhibited a low detection limit to 0.17 fM, providing a new avenue for sensitive, fast and reliable sensing of various DNA/RNA.

Label-free immunosensing of telomerase using bio-conjugation of biotinylated antibody to poly(chitosan) gold nanoparticles

Aim: This study aimed to establish a label-free electrochemical biosensor for telomerase detection in human biofluid. Method: Synthesized green nanocomposite (poly[chitosan] decorated by gold nanoparticles) was used for the efficient immobilization of biotinylated antibody of telomerase and immunocomplex of antigen-antibody. Poly(chitosan) was decorated by gold nanoparticles on the surface of a glassy carbon electrode using an electrochemical coating technique. Results: The constructed immunosensor exhibited wide dynamic range (0.078-160 IU/ml-1) with a low limit of quantification of 0.078 IU/ml-1, which present a unique manner for telomerase assays in early prognosis for cancers. Conclusion: This study encourages scientists and scholars to design and develop new biosensor platforms for point-of-care diagnostics for telomerase management, an interesting reference for future research.

Bio-inspired nanozyme with ultra-thin Fe-Bi2O2S nanosheets for in-situ amplified photoelectrochemical immunoassay of cancer-related protein

A Fe-loaded Bi₂O₂S nanosheet photoanode serving as photoelectric biomonitoring platform for the detection of prostate-specific antigen (PSA) using biologically inspired prussian nanoparticle (PB)-catalyzed biocatalytic precipitation strategy was developed. Primarily, the signal probe PB-mAb₂ obtained by electrostatic adsorption was immobilized on a microplate in the presence of target PSA, and 4-chloro-1-naphthol (4-CN) was oxidized to benzo-4-chloro-hexadienone (4-CD) with the assistance of exogenous hydrogen peroxide, which was generated by a large number of hydroxyl radicals catalyzed by PB. The generated 4-CD showed strongly low conductivity characteristics to burst the photocurrent of highly photoactive Fe-Bi₂O₂S photoanode. The split incubation reaction could be suitable for high volume and low-cost rapid detection. A dynamic response range of 0.1-100 ng mL^-1 with a limit of detection of 34.2 pg mL^-1 was achieved with the sensor based on a photoelectric sensing platform and a biomimetic catalytic precipitation reaction. Equally important, the sensor also showed good potential in the detection of real samples compared to commercially available ELISA kits. In conclusion, this work provides a fresh scheme for the development of sensitive biosensors through a bio-inspired catalytic strategy of versatility and a photoanode coupling with high photoelectric activity.