A photoelectrochemical immunosensor based on Z-scheme CdS composite heterojunction for aflatoxin B1

Biofunctional photoelectrochemical/electrochemical immunosensor based on BiVO4/BiOI-MWCNTs and Au@PdPt for alpha-fetoprotein detection

A biofunctional immunosensor combining photoelectrochemical (PEC) and electrochemical (EC) was proposed for the quantitative detection of the liver cancer marker alpha-fetoprotein (AFP) in human blood. BiVO4/BiOI-MWCNTs photoactive materials were first prepared on conductive glass FTO, and the photoelectrode was functionalized by chitosan and glutaraldehyde. Then, the AFP capture antibody (Ab1) was successfully modified on the photoelectrode, and the label-free rapid detection of AFP antigen was achieved by PEC. In addition, Au@PdPt nanospheres were also used as a marker for binding to AFP detection antibody (Ab2). Due to the excellent catalytic properties of Au@PdPt in EC reaction, a signal increase in the EC response can be achieved when Ab2 binds to the AFP antigen, which ensures high sensitivity for the detection of AFP. The detection limits of PEC and EC are 0.050 pg/mL and 0.014 pg/mL, respectively. The sensor also possesses good specificity, stability and reproducibility, shows excellent performance in the detection of clinical samples and has good clinical applicability.

Colorimetric and ECL dual-mode aptasensor for smartphone-based onsite sensitive detection of aflatoxin B1 in combination with ZnO@MWCNTs/g-C3N4 nanosheets and CuO@CuPt nanocomposites

The development of dual-mode strategies with superior sensitivity and accuracy have garnered increasing attention for researchers in Aflatoxin B1 (AFB1) analysis. Herein, a colorimetric-electrochemiluminescence (ECL) dual-mode biosensor was constructed for onsite and ultrasensitive determination of AFB1. The multi-wall carbon nanotubes (MWCNTs) were integrated with the ZnO metal organic frameworks (MOFs) to accelerate the electron transfer and boost the ECL intensity of g-C3N4 nanoemitters. Through the aptamer-based DNA sandwich assay, the CuO@CuPt nanocomposites were introduced onto the electrode and acted as the dual functional signal nanoprobes. Due to the good spectrum overlap between the CuO@CuPt nanoprobes and g-C3N4 nanosheets, ECL signal could be efficiently quenched. Additionally, the CuO@CuPt nanoprobes show superior catalytic properties towards the TMB and H2O2 colorimetric reactions, and an obvious color alteration from colorless to blue can be observed using the smartphone. Under optimized conditions, a sensitive and accurate dual-mode analysis of the AFB1 was accomplished with the colorimetric detection limit of 3.26 fg/mL and ECL detection limit of 0.971 fg/mL (S/N = 3). This study combines innovative nanomaterial properties of ZnO@MWCNTs, g-C3N4 and CuO@CuPt for ultrasensitive dual-mode detection, which offers new opportunities for the innovative engineering of the dual-mode sensors and demonstrates significant potential in food safety analysis.

A signal-on photoelectrochemical aptasensor based on WO3/CdS heterojunction for the ultrasensitive detection of kanamycin

In this study, a signal-on photoelectrochemical (PEC) aptasensor for the ultrasensitive determination of kanamycin (KANA) was constructed using WO3/CdS heterojunction as photoactive material. Firstly, WO3/CdS heterojunction with excellent photoelectric response was successfully prepared by simple co-precipitation method, resulting in a strong and stable initial photocurrent. In addition, amino modified aptamers were immobilized on the electrode surface by glutaraldehyde as biological recognition components. In the presence of the target KANA, it is specifically recognized and captured by the aptamers. More importantly, KANA can act as a signal amplifier to enhance the photocurrent due to the oxidation of KANA by photogenerated holes. Therefore, a signal-on PEC aptasensor based on WO3/CdS heterojunction with high selectivity was obtained for the detection of KANA. Under optimized experimental conditions, the PEC aptasensor demonstrated a wide linear range of 10 pM to 400 nM, with a detection limit of 6.77 pM. Meanwhile, the designed PEC aptasensor had been successfully utilized for the analytical examination of milk, fish, serum, and water samples.

Enzyme-like nanoparticle-engineered mesenchymal stem cell secreting HGF promotes visualized therapy for idiopathic pulmonary fibrosis in vivo

Stem cell therapy is being explored as a potential treatment for idiopathic pulmonary fibrosis (IPF), but its effectiveness is hindered by factors like reactive oxygen species (ROS) and inflammation in fibrotic lungs. Moreover, the distribution, migration, and survival of transplanted stem cells are still unclear, impeding the clinical advancement of stem cell therapy. To tackle these challenges, we fabricate AuPtCoPS trimetallic-based nanocarriers (TBNCs), with enzyme-like activity and plasmid loading capabilities, aiming to efficiently eradicate ROS, facilitate delivery of therapeutic genes, and ultimately improve the therapeutic efficacy. TBNCs also function as a computed tomography contrast agent for tracking mesenchymal stem cells (MSCs) during therapy. Accordingly, we enhanced the antioxidant stress and anti-inflammatory capabilities of engineered MSCs and successfully visualized their biological behavior in IPF mice in vivo. Overall, this study provides an efficient and forward-looking treatment approach for IPF and establishes a framework for a stem cell-based therapeutic system aimed at addressing lung disease.

Virtual Screening and Validation of Affinity DNA Functional Ligands for IgG Fc Segment

The effective attachment of antibodies to the immune sensing interface is a crucial factor that determines the detection performance of immunosensors. Therefore, this study aims to investigate a novel antibody immobilization material with low molecular weight, high stability, and excellent directional immobilization effect. In this study, we employed molecular docking technology based on the ZDOCK algorithm to virtually screen DNA functional ligands (DNAFL) for the Fc segment of antibodies. Through a comprehensive analysis of the key binding sites and contact propensities at the interface between DNAFL and IgG antibody, we have gained valuable insights into the affinity relationship, as well as the principles governing amino acid and nucleotide interactions at this interface. Furthermore, molecular affinity experiments and competitive binding experiments were conducted to validate both the binding ability of DNAFL to IgG antibody and its actual binding site. Through affinity experiments using multi-base sequences, we identified bases that significantly influence antibody-DNAFL binding and successfully obtained DNAFL with an enhanced affinity towards the IgG Fc segment. These findings provide a theoretical foundation for the targeted design of higher-affinity DNAFLs while also presenting a new technical approach for immunosensor preparation with potential applications in biodetection.

Novel portable photoelectrochemical sensor based on CdS/Au/TiO2 nanotube arrays for sensitive, non-invasive, and instantaneous uric acid detection in saliva

Uric acid (UA) monitoring is the most effective method for diagnosis and treatment of gout, hyperuricemia, hypertension, and other diseases. However, challenges remain regarding detection efficiency and rapid on-site detection. Here, we first synthesized a CdS/Au/TiO2-NTAs Z-scheme heterojunction material using a titanium dioxide nanotube array (TiO2-NTAs) as the substrate and modified with gold nanoparticles (Au) and cadmium sulfide particles (CdS). This material achieves bandgap alignment to generate a large number of electron-hole pairs under illumination. Then, using CdS/Au/TiO2-NTAs as the working electrode and molecularly imprinted polymers (MIP) as the recognition unit, we constructed a portable photoelectrochemical (PEC) sensor for non-invasive instant detection of UA concentration in human saliva, which has unique advantages in the field of high-sensitivity PEC instant detection. The portable MIP-PEC sensor achieves a linear range of 0.01-50 μM and a detection limit as low as 5.07 nM (S/N = 3). At the same time, the portable MIP-PEC sensor exhibits excellent sensitivity, specificity as well as stability, and shows no statistically significant difference compared to traditional high-performance liquid chromatography (HPLC) in practical sample detection. Compared to traditional PEC modes, this work demonstrates a novel and universal method for high-sensitivity instant detection in the field of PEC.

Dual modal improved enzyme-linked immunosorbent assay for aflatoxin B1 detection inspired by the interaction of amines with Prussian blue nanoparticles

This work reports an improved enzyme-linked immunosorbent assay (ELISA) via the interaction between prussian blue nanoparticles (PBNPs) and amines for aflatoxin B1 (AFB1) detection. The effect of different amines on the structure and properties of PBNPs was systematically investigated. Amines with pKb < 7, like ethylenediamine (EDA), can decompose structure of PBNPs, leading to the reduction of extinction coefficient and photothermal effect. Whereas, amines with large pKb > 7, such as o-phenylenediamine (OPD), could undergo catalytic oxidation by PBNPs, resulting in the production of fluorescent and colored oxidation products. Accordingly, EDA and OPD were used to construct improved ELISA. Specifically, silica nanoparticles, on which AFB1 aptamer and amino binding agent (ethylenediaminetetraacetic acid disodium salt, EDTA•2Na) were previously assembled via carboxyl-amino linkage, are anchored to microplates by AFB1 and antibody. EDA concentration can be regulated by EDTA•2Na to affect extinction coefficient and photothermal effect of PBNPs, thereby achieving visual colorimetric and portable photothermal signal readout (Model 1). OPD concentration can also be controlled by EDTA•2Na, thus generating colorimetric and ultrasensitive fluorescent signals through PBNPs catalysis (Model 2). The proposed strategy not only opens new avenue for signal readout mode of biosensing, but also provides universal technique for hazards.

Europium nanospheres based ultrasensitive fluorescence immunosensor for aflatoxin B1 determination in feed

In this work, a new competitive immunosensor for aflatoxin B1 (AFB1) detection was developed using europium (Eu) fluorescent nanospheres and magnetic beads. Firstly, Eu nanospheres were synthesized through two steps including carboxylated polystyrene nanospheres and Eu-doped polystyrene nanospheres preparation. Then Eu nanospheres were covalently tagged to anti-AFB1 monoclonal antibody (anti-AFB1 mAb) through an EDC coupling method. Carboxylated Fe3O4 magnetic beads were conjugated to AFB1-BSA through EDC/NHS crosslinking to obtain AFB1-BSA-Fe3O4. In the absence of AFB1, Eu-anti-AFB1 mAb were incubated with AFB1-BSA-Fe3O4 to form Eu-anti-AFB1 mAb-AFB1-BSA-Fe3O4 in PBS buffer. However, in the presence of AFB1, the competitive interaction of AFB1 and AFB1-BSA-Fe3O4 to bind with Eu-anti-AFB1 mAb occurred. With the increasing concentration of AFB1, less Eu-anti-AFB1 mAb-AFB1-BSA-Fe3O4 formed. So the fluorescence intensity of Eu-anti-AFB1 mAb-AFB1-BSA-Fe3O4 was gradually decreased after magnetic separation. The degree of fluorescence decrease was linear with respect to the logarithm of AFB1 concentration in the range of 0.01-2 ng/mL in both buffer solution and feed samples and the detection limit was 0.003 ng/mL. What's more, the immunosensor showed excellent specificity for AFB1 without being interfered by other mycotoxins. In consideration of the excellent performance of this immunosensor, we can speculate that the proposed method could be widely used in detecting food contaminants.

Nafion-Immobilized Functionalized MWCNT-based Electrochemical Immunosensor for Aflatoxin B1 Detection

The ubiquitous aflatoxin B1 (AFB1) contamination in foods and other complex matrices has brought great challenges for onsite monitoring. In this study, an ultrasensitive Nafion-immobilized functionalized multiwalled carbon nanotube (MWCNT)-based electrochemical (EC) immunosensor was developed for trace AFB1 detection. The introduced Nafion film could steadily stabilize functionalized MWCNTs with uniform distribution and tiling on the surface of a Au electrode. Functionalized MWCNTs with a large specific surface area, numerous active sites to couple with abundant anti-AFB1 monoclonal antibodies (mAbs), and high conductivity served as the signal amplifier for remarkably enhancing the sensing performance of the immunosensor. In the presence of AFB1, it was specifically captured by mAbs to reduce the amplified current signals, which were recorded by differential pulse voltammetry for the accurate quantitation of AFB1. Because of the synergistic effects of Nafion on the stabilization of functionalized MWCNTs as signal enhancers, the developed EC immunosensor exhibited an extremely high selectivity, excellent sensitivity with a limit of detection as low as 0.021 ng/mL, and a wide dynamic range of 0.05-100 ng/mL, besides fascinating merits of easy construction, low cost, good stability in 7 days, and good reusability. The anti-interference ability of the immunosensor was verified against three other mycotoxins, and the practicability and accuracy were confirmed by measuring AFB1 in fortified malt, lotus seed, and hirudo samples with a satisfactory recovery of 92.08-104.62%. This novel immunosensing platform could be extended to detect more mycotoxins in complex matrices to ensure food safety.

Integrating multiple probes for simplifying signal-on photoelectrochemical biosensing of microRNA with ultrasensitivity and wide detection range based on biofunctionalized porous ferroferric oxide and hypotoxic quaternary semiconductor

A facile and signal-on photoelectrochemical (PEC) biosensing strategy was designed based on hypotoxic Cu2ZnSnS4 NPs nanoparticles (NPs) and biofunctionalized Fe3O4 NPs that integrated recognition units with signal elements, without the need for immobilization of probes on the electrode. Cu2ZnSnS4 NPs were used as the PEC substrate to produce intensive and stable photocurrent. The porous magnetic Fe3O4 NPs displayed favorable loading capacity for CdS QDs and easy biofunctionalization by negatively charged capture DNA (cDNA). cDNA sealed the pore of Fe3O4 NPs, avoiding the escape of CdS QDs as a PEC sensitizer. After hybridizing with target microRNA (miRNA), cDNA split away off Fe3O4 NPs whose porous channel might open and release sealed CdS QDs (signal element), resulting in a dramatical enhancement of PEC response. Herein, miRNA hardly contacted with CdS QDs, effectively avoiding harm to the target miRNA. This proposed strategy simplified procedures of assembly and made the biorecognition process sufficient for promoting a stationary quantity of probes, which was expected to obtain satisfactory performance for bioassay. Using miRNA-155 as a model analyte and combining with duplex-specific nuclease (DSN)-assisted amplification, a simplified and signal-on PEC biosensing platform for miRNA-155 with wonderful performance was proposed. DSN-assisted amplification further promoted PEC signal increment, leading to ulteriorly improving sensitivity (detection limit of 0.17 fM) and linear range (6.5 orders of magnitude) for miRNA-155 assay. Moreover, the developed PEC biosensing platform exhibited satisfactory stability, excellent specificity, and favorable accuracy for miRNA-155, which would have a promising prospect for monitoring miRNA expression in tumor cells.

Biosensors based on core-shell nanoparticles for detecting mycotoxins in food: A review

Mycotoxins are toxic metabolites produced by fungi in the process of infecting agricultural products, posing serious threat to the health of human and animals. Thus, sensitive and reliable analytical techniques for mycotoxin detection are needed. Biosensors equipped with antibodies or aptamers as recognition elements and core-shell nanoparticles (NPs) for the pre-treatment and detection of mycotoxins have been extensively studied. By comparison with monocomponent NPs, core-shell nanostructures exhibit unique optical, electric, magnetic, plasmonic, and catalytic properties due to the combination of functionalities and synergistic effects, resulting in significant improvement of sensing capacities in various platforms, such as surface-enhanced Raman spectroscopy, fluorescence, lateral flow immunoassay and electrochemical sensors. This review focused on the development of core-shell NPs based biosensors for the sensitive and accurate detection of mycotoxins in food samples. Recent developments were categorised and summarised, along with detailed discussion of advantages and shortcomings. The future potential of utilising core-shell NPs in food safety testing was also highlighted.

Intelligent Electrochemical Point-of-Care Test Method with Interface Control Based on DNA Pyramids: Aflatoxin B1 Detection in Food and the Environment

Sensitive, intelligent point-of-care test (iPOCT) methods for small molecules like aflatoxin B1 (AFB1) are urgently needed for food and the environment. The challenge remains of surface control in iPOCT. Herein, we developed an electrochemical sensor based on the DNA pyramid (DNP), combining a smartphone, app, and mobile electrochemical workstations to detect AFB1. The DNP's structure can reduce local overcrowding and entanglement between neighboring probes, control the density and orientation of recognition probes (antibodies), produce uniform and orientational surface assemblies, and improve antigen-antibody-specific recognition and binding efficiency. Simultaneously, the hollow structure of the DNP enhances the electron transfer capacity and increases the sensitivity of electrochemical detection. In this work, the biosensor based on DNP was first combined with electrochemical (Ec) iPOCT to simultaneously achieve ordered interface modulation of recognition probes and intelligent detection of AFB1. Under optimal conditions, we found a detection limit of 3 pg/mL and a linear range of 0.006-30 ng/mL (R2 = 0.995). Further, using peanut, soybean, corn, and lake water as complex matrices, it recorded recoveries of 82.15-100.53%, excellent selectivity, acceptable stability, and good reproducibility. Finally, this Ec iPOCT provides consistent results compared to the high-performance liquid chromatography-tandem mass spectrometry method.

A self-powered photoelectrochemical biosensing platform for H-FABP monitoring mediated by CsPbBr3@COF-V

Advanced bioelectronic detection based on the integration of modern optical electronics and biological systems has a broad prospect. The strategy of cathode signal amplification in self-powered photoelectrochemical (PEC) immunosensors with excellent performance is rarely reported in the field of immune analysis. Herein, the work demonstrates a self-powered PEC biosensor formed with BiOI photocathode and WO3/SnS2/ZnS photoanode, and CsPbBr3@COF-V was used as the photocathode signal quenching source for the quantitative monitoring of heart fatty acid binding protein (H-FABP). The high efficiency and stable self-powered biosensor formed not only provides continuous and powerful photocurrent response for bioanalysis through reasonable stepped band structure, but also effectively eliminates the interference of reducing substances. The quenching source CsPbBr3@COF-V greatly affects the photocurrent response due to steric hindrance, weak conductivity, competition with the substrate for dissolved oxygen and excitation light source. And the intervention of this key factor achieves multiple signal amplification effect and opens up an innovative vision for self-powered PEC immunosensor. Taking H-FABP as a representative analyte, the proposed signal amplification self-powered photoelectrochemical presents a broad linear range from 0.0005 to 150 ng/mL with the detection limit of 0.19 pg/mL.

A signal-off photoelectrochemical sandwich-type immunosensor based on WO3/TiO2 Z-scheme heterojunction

A sandwich "signal-off" type photoelectrochemical (PEC) immunosensor was fabricated based on a composite heterojunction of tungsten oxide/titanium oxide microspheres (WO3/TiO2) acting as signal amplification platform and carbon microspheres loaded by gold nanoparticles (Cs@Au NPs) utilized as the label for detecting antibody. WO3/TiO2 had excellent photoelectric performance, and the results of Mott-Schottky plots, open-circuit voltage, and electron spin resonance spectroscopy indicated that it belonged to the Z-scheme heterojunction transfer mechanism of photogenerated carriers. To achieve the sensitization of PEC immunosensor, Cs@Au NP-labeled immunocomplex can effectively reduce the photocurrent signal. The PEC immunosensors were fabricated under the optimal conditions of 1:1 WO3/TiO2 (molar ratio), 2.0 mg mL-1 WO3/TiO2, and 1.5 mg mL-1 Cs@Au NPs. Through comparison of the detection results of label-free and sandwich-type PEC immunosensors for nucleocapsid (N) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), we found that the sensitivity of the sandwich type was 2.53 times the label-free type, and the limit of detection was 0.006 ng mL-1, i.e., 3.17 times lower than the label-free type. This demonstrates that the developed sandwich-type PEC immunosensor will have a brighter application prospect.

Magnetic relaxation switching immunoassay based on "limited-magnitude" particles for sensitive quantification of aflatoxin B1

Aflatoxin B₁ (AFB₁) is a highly toxic and carcinogenic chemical substance that endangers food safety and human health. Magnetic relaxation switching (MRS) immunosensors are utilized in a variety of applications in food analysis due to its resistance to matrix interferences, but they often suffer from magnetic separation-based multi-washing steps and low sensitivity. Herein, we propose novel MRS strategy for the sensitive detection of AFB₁ using "Limited-Magnitude" size particles: a single millimeter sized polystyrene spheres (PS_mm) and 150 nm superparamagnetic nanoparticles (MNP₁₅₀). Only a single PS_mm is used as the microreactor to enhance all of the magnetic signal on its surface in high concentration by an immune competitive response, successfully preventing signal dilution, which can be transferred by pipette, simplifying the process of separation and washing. The established single polystyrene sphere magnetic relaxation switch biosensor (SMRS) was able to quantify AFB₁ from 0.02 to 200 ng/mL with a detection limit of 14.3 pg/mL. SMRS biosensor has been successfully used for the detection of AFB₁ in wheat and maize samples, and the results in agreement with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS). Benefiting from high sensitivity and convenient operation, the simple and enzyme-free method is promising in trace small molecules applications.

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.

In situ synthesized eRAFT polymers for highly sensitive electrochemical determination of AFB1 in foods and herbs

An electrochemical sensor based on environmentally friendly eRAFT polymerization was developed for the detection of aflatoxin B₁ (AFB₁) in food and herbal medicine. Two biological probes, aptamer (Ap) and antibody (Ab), were used to specifically recognize AFB₁, and a large number of ferrocene polymers were grafted on the electrode surface by eRAFT polymerization, which greatly improved the specificity and sensitivity of the sensor. The detection limit of AFB₁ was 37.34 fg/mL. In addition, the recovery rate was 95.69% to 107.65% and the RSD was 0.84% to 4.92% by detecting 9 spiked samples. The delighted reliability of this method was verified by HPLC-FL.

A photoelectrochemical immunosensor based on magnetic all-solid-state Z-scheme heterojunction for SARS-CoV-2 nucleocapsid protein detection

Rapid, convenient and accurate detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is urgently needed to timely diagnosis of coronavirus pandemic (COVID-19) and control of the epidemic. In this study, a signal-off photoelectrochemical (PEC) immunosensor was constructed for SARS-CoV-2 nucleocapsid (N) protein detection based on a magnetic all-solid-state Z-scheme heterojunction (Fe₃O₄@SiO₂@TiO₂@CdS/Au, FSTCA). Integrating the advantages of magnetic materials and all-solid-state Z-scheme heterostructures, FSTCA was implemented to ligate the capture antibody to form magnetic capture probe (FSTCA/Ab₁). It can simplify the separation and washing process to improve reproducibility and stability, while allowing immune recognition to be performed in the liquid phase instead of the traditional solid-liquid interface to improve anti-interference. Besides, the heterojunction inhibited the recombination of photogenerated electron/hole (e^-/h⁺) and promoted the light absorption to provide superior photoelectric substrate signal. The mechanism of photogenerated e^-/h⁺ transfer of FSTCA were investigated by the electron spin resonance (ESR) spectroscopy. SiO₂ spheres loaded with Au NPs utilized as an efficient signal quencher. The steric hindrance effect of SiO₂@Au labeled detection antibodies (SiO₂@Au-Ab₂) conjugates significantly diminished light absorption and hindered the transfer of photogenerated electrons, further amplifying the signal change value. Based on the above merits, the elaborated immunosensor had a wide linear range of 10 pg mL^-1-100 ng mL^-1 and a low detection limit down to 2.9 pg mL^-1 (S/N = 3). The fabricated PEC immunosensor demonstrated strong anti-interference, easy operation, and high sensitivity, showing enormous potential in clinical diagnosis of SARS-CoV-2.

Trimetallic Au@Pd@Pt nanozyme-enhanced lateral flow immunoassay for the detection of SARS-CoV-2 nucleocapsid protein

The rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seriously threatened global public health. Establishing a rapid and sensitive diagnostic test for early detection of the SARS-CoV-2 nucleocapsid protein is urgently required to defend against the pandemic. Herein, an enhanced lateral flow immunoassay (LFIA) was fabricated by trimetallic Au@Pd@Pt core-shell nanozymes for detection of the SARS-CoV-2 nucleocapsid protein. The Au@Pd@Pt nanozymes (Au@Pd@Pt NZs) synthesized via a one-pot method, with a dendrite morphology and uniform particle size, showed excellent peroxidase-like activity. Due to the perfect enzyme-like catalytic activity toward 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H₂O₂), the catalytic signal could be generated even by a tiny amount of Au@Pd@Pt NZs accumulated on the test strip. Therefore, rapid detection with higher sensitivity was achieved. The Au@Pd@Pt NZs-based LFIA provided a quantitative range of 0.05-100 ng mL^-1 with a limit of detection of 0.037 ng mL^-1, which was 17-fold lower than the LFIA without enhancement. The average recoveries from spiked samples were in the range of 92.5-107.9% with relative standard deviations all less than 4%, indicating the reliability and repeatability of the proposed LFIA. Additionally, the proposed LFIA could report results within 30 min using a microplate reader. In conclusion, the Au@Pd@Pt NZs-LFIA is a rapid, simple, and sensitive method for detecting the SARS-CoV-2 nucleocapsid protein.