Graphene oxide-based colorimetric/fluorescence dual-mode immunochromatography assay for simultaneous ultrasensitive detection of respiratory virus and bacteria in complex samples

Genetic engineering-powered dual-mode lateral flow immunosensor for colorimetric and fluorescent detection of ochratoxin A in pepper

Ochratoxin A (OTA) poses significant risks to both environment and human health, necessitating the development of rapid and sensitive detection methods. Lateral flow immunosensors (LFIs) typically use monoclonal antibodies and artificial antigens for mycotoxin detection; however, the preparation of these components is time-intensive, laborious, costly, and environmentally harmful. Herein, we developed an innovative genetic engineering-powered colorimetric/fluorescent dual-mode LFI (CM/FL-dLFI) using nanobodies and the mimotope peptide (MP) of OTA. Initially, a heptameric bifunctional fusion (sfGFP-C4bpα-Y4) containing the superfolder green fluorescent protein, the C4-binding protein α-chain, and the MP Y4 was constructed. The fusion was subsequently labeled on gold nanoflowers (AuNFs) to create the AuNFs@sfGFP-C4bpα-Y4 probe, which can be captured by the nanobody heptamer (Nb-C4bpα) and provides colorimetric/fluorescent signals. The optimized CM/FL-dLFI achieved a colorimetric limit of detection (LOD) of 0.01 ng/mL and a fluorescent LOD of 0.05 ng/mL. It exhibited high selectivity for OTA, good recovery rates of 82.85-102.81 % with relative standard deviations not exceeding 14 %, and excellent long-term stability. Moreover, it showed strong correlation with high-performance liquid chromatography in the analysis of 11 real pepper samples. Therefore, this study highlights the promising application potential of nanobodies and MPs in developing an economical and eco-friendly LFI for OTA detection in pepper.

Nanozyme-Catalyzed Colorimetric Microfluidic Immunosensor for the Filtration Enrichment and Ultrasensitive Detection of Salmonella typhimurium in Food Samples

Rapid screening of foodborne pathogens is crucial to prevent food poisoning. In this study, we proposed a nanozyme-catalyzed colorimetric microfluidic immunosensor (Nano-CMI) for the filtration enrichment and ultrasensitive detection of Salmonella typhimurium in complex matrices. Gold-core porous platinum shell nanopompoms (Au@Pt nanopompoms) were synthesized with excellent peroxidase-like activity to oxidize 3,3',5,5'-tetramethylbenzidine with significant color change. The Au@Pt nanopompoms demonstrated a large reaction area, superior catalytic property, and good stability. The microfluidic chip used in the Nano-CMI was designed based on the size disparities among S. typhi, Au@Pt nanopompoms, and the pore sizes of filters I and II. Thus, a biosensor containing pretreatment, incubation, enrichment, and detection of four-in-one functions was established and performed under the drive of a medical plastic syringe. This biosensor can accomplish ultrasensitive detection of S. typhi with a limit of detection as low as 9 cfu/mL within 20 min, which makes it suitable for point-of-care testing. The proposed Nano-CMI also possessed high specificity and good repeatability (RSD < 2.1%) and can thus be applied directly to the analysis of real food samples, suggesting its great potential for practical application in the food safety field.

Development of a graphene oxide multilayer quantum dot-based immunochromatographic strip for the ultrasensitive detection of H7 subtype avian influenza viruses

Since March 2013, the H7N9 subtype of avian influenza virus (AIV) has become an important zoonotic infectious disease, garnering significant global attention because of its potential to affect human health. Establishing a rapid, effective, and sensitive method to detect H7 subtype AIVs is crucial for disease control. In this study, we developed a graphene oxide multilayer quantum dot-based immunochromatographic strip for the ultrasensitive detection of H7 subtype AIVs. The method demonstrated excellent sensitivity, with a limit of detection of 0.063 hemagglutinin units and 0.016 ng/ml for the hemagglutinin protein. The method exhibited remarkable specificity, with no reaction with other subtypes of influenza A virus andno cross-reactivity with other types of avian virus. Additionally, this method exhibited excellent reproducibility, with both inter-group and intra-group variations remaining below 10 %. Preliminary testing on avian clinical samples showed impressive consistency, underscoring the method's reliability. These initial results suggest that this detection approach has significant potential for widespread use in analyzing avian clinical samples, indicating substantial promise for its future application in various diagnostic settings.

"Integrated Stacked" Design "Nanobullet" for High Photothermal Conversion in Dual-Mode Lateral Flow Immunoassay

Salmonella enterica serovar typhimurium (S. typhimurium), a prevalent foodborne bacterium, necessitates creating sensitive and rapid detection methods for food safety, with lateral flow immunoassays (LFIAs) using nanomaterials as signal tracers being particularly effective. Enhancements in performance and sensitivity are not restricted to the material alone, we propose an "integrated stacked" concept, which combines amorphous active sites, hollow morphology for enhanced reflection, and symmetric structure for strong absorption resonance. This approach leads to significant photothermal enhancement (η = 60.66%) and is supported by finite element analysis (|E|max2 = 3100). A hollow "nanobullet" (RuTe2) was created, featuring a vivid colorimetric signal enhancing the detection range, a large specific surface area (≈6:1) for improved antibody binding, and excellent photothermal properties facilitating dual-mode transduction. After 5 min of binding, the detection limits of RuTe2-LFIA for S. typhimurium after 12 min were 2398.83 cfu mL-1 (colorimetric) and 977.23 cfu mL-1 (photothermal), which were 36.14 and 88.72 times lower than the values of AuNPs-LFIA (86696.19 cfu mL-1). The superior performance of RuTe2-LFIA suggests potential advancements in photothermal materials for point-of-care testing.

Two-Dimensional Nanozyme-Catalyzed Colorimetric CRISPR Assay for the Microfluidic Detection of Monkeypox Virus

The recent monkeypox epidemic outbreaks worldwide highlight the urgent need for fast and precise diagnostic solutions, especially in resource-limited settings. Here, a two-dimensional nanozyme-catalyzed colorimetric CRISPR assay for the microfluidic detection of the monkeypox virus (MPXV) was established. We utilized graphene oxide as a substrate for the adsorption of gold seeds and the deposition of a porous Pt shell to prepare high-performance two-dimensional GO@Pt nanomaterials. The viral nucleic acids released from clinical samples initiated a single-step recombinase polymerase amplification-CRISPR/Cas13a for the trans-cleavage of ssRNA reporters labeled with FAM and biotin. These reporters can be recognized by FAM antibody-conjugated GO@Pt nanozymes and streptavidin-coated magnetic beads. The formed sandwich immunocomplexes can catalyze the oxidation of a colorless 3,3',5,5'-tetramethylbenzidine substrate with a distinct color change. The proposed GO@Pt-catalyzed colorimetric CRISPR assay exhibited a limit of detection of 1 copy/μL of MPXV in 60 min. Forty clinical samples, including rash fluid swabs and oral swabs, were tested with 100% agreement with the real-time PCR. These results indicate the excellent potential of GO@Pt-catalyzed colorimetric CRISPR for the sensitive and accurate testing of MPXV under resource-constrained conditions.

Dual-mode immunochromatographic test strips based on aggregation-induced luminescence nanoprobes for the detection of ZEN in corn

Zearalenone (ZEN) is a secondary metabolite produced by various Fusarium species. Its widespread contamination has raised deep concern globally. Also, ZEN is reproductively toxic, hepatotoxic and carcinogenic. Rapid detection methods for ZEN mainly suffer from the aggregation-caused quenching (ACQ) effect of fluorescent materials. Therefore, there is an urgent need to develop new methods for detecting ZEN. On this basis, we synthesised AIE polymer microspheres (AIEPMs) using aggregation-induced emission (AIE) dyes. We coupled these microspheres with antibodies to prepare immunoprobes to establish immunochromatographic test strips with a colorimetric/fluorescent dual mode. Under optimal parameters, the visual limit of detection (vLOD) for the colorimetric mode was 0.625 ng mL-1. In comparison, the quantitative limit of detection (qLOD) for the fluorescent mode was as low as 0.039 ng mL-1. The average recoveries ranged from 97.60% to 102.46%, and the coefficients of variation (CV) ranged from 2.10% to 10.70%. These data demonstrate the excellent reproducibility and reliability of the established method. The researchers have successfully applied the method for accurate sample detection. The method demonstrated the great potential of AIEPMs-ICA as a colorimetric/fluorescent dual-mode test strip for the rapid detection of ZEN.

Fabric-based visualization biosensor for real-time environmental monitoring and food safety

Foodborne and waterborne bacterial infections caused by Escherichia coli (E. coli) pose a serious threat to public health and safety. Therefore, there is an urgent need to develop a fast and accurate diagnostic device for early detection and prevention of bacterial contamination. In this study, we designed a visual cotton fabric-based detection biosensor that can target enzymes produced by E. coli metabolism and induce color changes. In addition, the system can be integrated with the naked eye, smartphones, and small spectrometers to analyze the generated signals for qualitative, semi-quantitative, and quantitative detection. The platform achieved a minimum detection limit of 537 cfu/mL for E. coli, a wide detection range of 102-106 cfu/mL, and a minimum detection time as low as 20 mins. The detection results of complex environmental samples showed that the system has excellent anti-ion interference and anti-pH interference behavior. This visual detection biosensor has great commercial application potential and can be widely used in real-time on-site detection due to its rapid, portable, anti-interference, and low-cost advantages.

Development of immunochromatographic and homogeneous assay based on quantum dot-functionalized polystyrene nanoprobes for the qualitative and quantitative screening of respiratory viruses

Accurately differentiating respiratory diseases caused by viruses is challenging because of the similarity in their early or clinical symptoms. Moreover, different infection sources require different treatments. However, the current diagnostic methods have limited differentiating efficiency and sensitivity. We developed a dual-system immunosensor with a bilayer fluorescent label as a signal amplifier for the on-site, sensitive, and accurate identification of multiple respiratory viruses (RVs). The nanomaterial, comprising a polystyrene (PS) nanosphere core encapsulated by two layers of CdSe@ZnS-COOH quantum dots (QDs), outperforms the conventional color and fluorescent labels in RV detection. The dual-system detection platform, comprising a PS@DQD-based lateral flow immunoassay (LFIA) and a PS@DQD-based homogeneous sensor, enables qualitative and quantitative screening of multiple respiratory viruses within 10 and 30 min, respectively, depending on the specific detection requirements for different application scenarios. This remarkable method provides 51.2 to 1000 times sensitivity improvement over commercial antigen detection kits and greater than 12.5 to 100 times improvement over QD-based immunosensors. Furthermore, we comprehensively evaluated the specificity, reproducibility, and stability of the integrated dual-system detection platform, demonstrating its reliability. Remarkably, the respiratory viral testing was validated using biological samples, thus illustrating its promise and convenience in the detection of respiratory viruses.

A facile optical sensing strategy for glyphosate detection based on structure-switching signaling aptamers

A facile and highly specific optical sensing strategy is established for glyphosate (GLYP) detection using structure-switching signaling aptamers (F-SSSAs) with fluorescence signal reporting functionality. The strategy involves two domains: the FITC-labeled signal transduction domain for fluorescence signal reporting, while the functional domain (specific structure-switching aptamers) controls the target recognition. Graphene oxide (GO) works as a robust F-SSSAs quencher in the absence of GLYP. However, the F-SSSAs structure is switched in the presence of GLYP, prominently affecting the interaction with GO. The fluorescence of the structure-switching signaling aptamer-based sensing system is subsequently restored. The present strategy exhibits two dynamic linear relationships for GLYP detection in the ranges 0.2 to 80 ng·mL-1 and 100 to 800 ng·mL-1, with a low detection limit (LOD) of 0.07 ng·mL-1. Significantly, the proposed sensing system has been successfully utilized to detect GLYP in water, soil, and rice, demonstrating its potential applications in GLYP monitoring.

Research progress on detection of foodborne pathogens: The more rapid and accurate answer to food safety

In recent years, foodborne diseases have posed a serious threat to human health, and rapid detection of foodborne pathogens is particularly crucial for the prevention and control of such diseases. This article offers a detailed overview of the development of detection techniques for foodborne pathogens, transitioning from traditional microbiological culture methods to the current array of techniques, including immunological, molecular biological, and biosensor-based methods. It summarizes the technical principles, advantages, disadvantages, and research progress of these diverse methods. Furthermore, the article demonstrates that the combination of different methods enhances the efficiency and accuracy of pathogens detection. Specifically, the article focuses on the application and advantages of combining CRISPR/Cas systems with other detection methods in the detection of foodborne pathogens. CRISPR/Cas systems, with their high specificity, sensitivity, and ease of operation, show great potential in the field of foodborne pathogens detection. When integrated with other detection techniques such as immunological detection techniques, molecular biology detection techniques, and biosensors, the accuracy and efficiency of detection can be further improved. By fully utilizing these tools, early detection and control of foodborne diseases can be achieved, enhancing public health and preventing disease outbreaks. This article serves as a valuable reference for exploring more convenient, accurate, and sensitive field detection methods for foodborne pathogens, promoting the application of rapid detection techniques, and ensuring food safety and human health.

Overview of the Design and Application of Dual-Signal Immunoassays

Immunoassays have been widely used for the determination of various analytes in the fields of disease diagnosis, food safety, and environmental monitoring. Dual-signal immunoassays are now advanced and integrated detection technologies with excellent self-correction and self-validation capabilities. In this work, we summarize the recent advances in the development of optical and electrochemical dual-signal immunoassays, including colorimetric, fluorescence, surface-enhanced Raman spectroscopy (SERS), electrochemical, electrochemiluminescence, and photoelectrochemical methods. This review particularly emphasizes the working principle of diverse dual-signal immunoassays and the utilization of dual-functional molecules and nanomaterials. It also outlines the challenges and prospects of future research on dual-signal immunoassays.

Optical lateral flow assays in early diagnosis of SARS-CoV-2 infection

So far, the 2019 novel coronavirus (COVID-19) is spreading widely worldwide. The early diagnosis of infection by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is essential to provide timely treatment and prevent its further spread. Lateral flow assays (LFAs) have the advantages of rapid detection, simple operation, low cost, ease of mass production, and no need for special devices and professional operators, which make them suitable for self-testing at home. This review focuses on the early diagnosis of SARS-CoV-2 infection based on optical LFAs including colorimetric, fluorescent (FL), chemiluminescent (CL), and surface-enhanced Raman scattering (SERS) LFAs for the detection of SARS-CoV-2 antigens and nucleic acids. The types of recognition components, detection modes used for antigen detection, labels employed in different optical LFAs, and strategies to improve the detection sensitivity of LFAs were reviewed. Meanwhile, LFAs coupled with different nucleic acid amplification techniques and CRISPR-Cas systems for the detection of SARS-CoV-2 nucleic acids were summarized. We hope this review provides research mentalities for developing highly sensitive LFAs that can be used in home self-testing for the early diagnosis of SARS-CoV-2 infection.

ICP-MS based detection method combined with Au NP and Ag NP labeling for bacteremia diagnosis

Bacteremia, as a serious infectious disease, has an increasing incidence and a high mortality rate. Early diagnosis and early treatment are crucial for improving the cure rate. In this work, we proposed an inductively coupled plasma mass spectrometry (ICP-MS)-based detection method combined with gold nanoparticle (Au NP) and silver nanoparticle (Ag NP) labeling for the simultaneous detection of Salmonella and Escherichia coli (E. coli O157:H7) in human blood samples. Salmonella and E. coli O157:H7 were captured by magnetic beads coupled with anti-8G3 and anti-7C2, and then specifically labeled by Au NP-anti-5H12 and Ag NP-anti-8B1 respectively, which were used as signal probes for ICP-MS detection. Under the optimal experimental conditions, the limits of detection of 164 CFU mL-1 for Salmonella, 220 CFU mL-1for E. coli O157:H7 and the linear ranges of 400-80,000 CFU mL-1Salmonella, 400-60,000 CFU mL-1 E. coli O157:H7 were obtained. The proposed method can realize the simultaneous detection of two types of pathogenic bacteria in human whole blood in 3.5 h, showing great potential for the rapid diagnosis of bacteremia in clinic.

Recent Advances in Lateral Flow Assays for Viral Protein Detection with Nanomaterial-Based Optical Sensors

Controlling the progression of contagious diseases is crucial for public health management, emphasizing the importance of early viral infection diagnosis. In response, lateral flow assays (LFAs) have been successfully utilized in point-of-care (POC) testing, emerging as a viable alternative to more traditional diagnostic methods. Recent advancements in virus detection have primarily leveraged methods such as reverse transcription-polymerase chain reaction (RT-PCR), reverse transcription-loop-mediated isothermal amplification (RT-LAMP), and the enzyme-linked immunosorbent assay (ELISA). Despite their proven effectiveness, these conventional techniques are often expensive, require specialized expertise, and consume a significant amount of time. In contrast, LFAs utilize nanomaterial-based optical sensing technologies, including colorimetric, fluorescence, and surface-enhanced Raman scattering (SERS), offering quick, straightforward analyses with minimal training and infrastructure requirements for detecting viral proteins in biological samples. This review describes the composition and mechanism of and recent advancements in LFAs for viral protein detection, categorizing them into colorimetric, fluorescent, and SERS-based techniques. Despite significant progress, developing a simple, stable, highly sensitive, and selective LFA system remains a formidable challenge. Nevertheless, an advanced LFA system promises not only to enhance clinical diagnostics but also to extend its utility to environmental monitoring and beyond, demonstrating its potential to revolutionize both healthcare and environmental safety.

Dual-mode colorimetric and fluorescence biosensors for the detection of foodborne bacteria

Due to the growing demand for detection technologies, there has been significant interest in the development of integrated dual-modal sensing technologies, which involve combining two signal transduction channels into a single technique, particularly in the context of food safety. The integration of two detection signals not only improves diagnostic performance by reducing assumptions, but also enhances diagnostic functions with increased application flexibility, improved accuracy, and a wider detection linear range. The top two output signals for emerging dual-modal probes are fluorescent and colorimetric, due to their exceptional advantages for real-time sensitive sensing and point-of-care applications. With the rapid progress of nanotechnology and material chemistry, the integrated colorimetric/fluorimetric dual-mode systems show immense potential in sensing foodborne pathogenic bacteria. In this comprehensive review, we present a detailed summary of various colorimetric and fluorimetric dual-modal sensing methods, with a focus on their application in detecting foodborne bacteria. We thoroughly examine the sensing methodologies and the underlying principles of the signal transduction systems, and also discuss the challenges and future prospects for advancing research in this field.