Simultaneous determination for A. flavus-metabolizing mycotoxins by time-resolved fluorescent microbead or gold-enabling test strip in agricultural products based on monoclonal antibodies

Multiple aptamer recognition-based quantum dot lateral flow platform: ultrasensitive point-of-care testing of respiratory infectious diseases

Respiratory infectious diseases spread rapidly and have a wide range of impacts, posing a serious threat to public health security. The development of a sensitive, accurate, and rapid detection method for respiratory viruses is crucial for disease prevention and control. However, existing methods are inadequate in satisfying the demand for accurate and convenient detection simultaneously. Therefore, an ultrasensitive point-of-care testing (POCT) platform based on a multiple aptamer recognition-based quantum dot lateral flow immunoassay (MARQ-LFIA) was developed in this work. This platform consisted of multiple high-affinity aptamers for recognizing different sites on a respiratory infectious virus protein, enhancing the efficiency of virus identification in complex environments. By combining a multiple aptamer recognition strategy with quantum dot fluorescent technique to construct LFIA test strips and pairing them with a high-gain portable fluorescence reader, excellent detection sensitivity and specificity were achieved in the case of coronavirus disease 2019 (COVID-19). The limits of detection were 1.427 pg mL-1 and 1643 U mL-1 towards the nucleocapsid protein and inactivated viruses, respectively, indicating that MARQ-LFIA improved detection sensitivity compared to reported methods. More critically, by testing thirty COVID-19 positive and twenty negative patient samples, the positive detection rate increased from 55.17% to 86.67% compared with commercially similar products. The universality of MARQ-LFIA was also investigated for diagnosing influenza B. We believe that MARQ-LFIA can be a promising POCT tool with potential applications in the areas of public health for the growing demand for precision diagnosis and treatment.

Biotin-labelled peptidomimetic for competitive time-resolved fluoroimmunoassay of benzothiostrobin

In recent years, more and more functional peptide ligands have been identified from phage display libraries and served the immunoassay of small molecules. After the identification, the phage particle instead limits further application of peptide ligands, so it is of great significance to explore the peptide ligand as an independent detection reagent. In this work, the identified peptidomimetic of benzothiostrobin was synthesized and labelled with biotin, which was combined with Eu³⁺-labelled streptavidin to develop the peptide-based time-resolved fluoroimmunoassay (P-TRFIA). Under the optimal conditions, the half-maximum inhibitory concentration (IC₅₀) of proposed P-TRFIA is 3.63 ng mL^-1, which is similar to the TRFIA using phage-borne peptidomimetic and Eu³⁺-labelled anti-phage antibody (IC₅₀: 4.55 ng mL^-1), also more sensitive than previously reported immunoassays for benzothiostrobin. In addition, the proposed P-TRFIA shows excellent specificity and accuracy for analysis of spiked samples, and its detection results shows good consistency with high-performance liquid chromatography for the detection of environment and agro-products samples with unknown benzothiostrobin concentrations.

Ultrasensitive Competitive Lateral Flow Immunoassay with Visual Semiquantitative Inspection and Flexible Quantification Capabilities

Antibiotics abuse has caused various problems threatening human health and ecological environment. Monitoring antibiotics residual levels is of great significance, yet still challenging for quantitative point-of-need testing with high-sensitivity and visual capability. Here we developed a competitive lateral flow immunoassay (CLFIA) platform with flexible readout for enrofloxacin (ENR), a regularly added antibiotic. To overcome the limitation of low sensitivity of traditional colloidal gold-based CLFIA, the three-dimensionally assembled gold nanoparticles (AuNPs) within dendritic silica scaffold were fabricated as signal reporters. The assembly structure effectively retained the intrinsic absorption features of hydrophobic AuNPs and greatly enhanced the light extinction ability of a single label for signal amplification. The obtained CLFIA strips can not only achieve qualitative screening of ENR at a very low concentration by naked eye (cutoff value: 0.125 ng/mL), but also enable ultrasensitive quantification of ENR by an optical scanner (limit of detection: 0.00195 ng/mL) or a smartphone (limit of detection: 0.0078 ng/mL). Moreover, to elaborate the visual inspection degree of CLFIA against traditional yes/no interpretation, a novel multirange gradient CLFIA strip was prepared for visually semiquantitative identification of ENR with four concentration ranges. The novel CLFIA platform demonstrated sensitive, specific, and reliable determination of ENR with flexible signal readout and provides a potential and invigorating pathway to point-of-need immunoassay of antibiotics.

Simultaneous determination of aflatoxins, fumonisin B1, T-2 and cyclopiazonic acid in agri-products by immunomagnetic solid-phase extraction coupled with UHPLC-MS/MS

In the present study, a rapid and sensitive determination method of seven mycotoxins was developed using immunomagnetic solid-phase extraction (IMPSE) coupled with UHPLC-MS/MS. Monoclonal antibodies were conjugated with CNBr superparamagnetic beads, and the major parameters affecting the IMPSE efficiency were systematically investigated. Under the optimized conditions, the mycotoxins were purified with the IMSPE procedure within 15 min and simultaneously quantified by UHPLC-MS/MS. Good linearities of the analytic method were established with the determination coefficients (R²) ranging from 0.9952 to 0.9997. The limit of quantifications were 0.04 µg kg^-1 ∼ 0.16 µg kg^-1, which fully satisfied the regulatory maximum levels. The recoveries were 84.5-112.7% with intra-day and inter-day precision less than 15.2%. Finally, the proposed IMSPE-UHPLC-MS/MS was successfully utilized to analyze seven mycotoxins in peanut, maize, and wheat, providing a simple and robust extraction and enrichment procedure of hydrophilic and zwitterionic analytes from complex matrix.

Construction of a TRFIC strip for rapid and sensitive detection of Ralstoniasolanacearum

The development of a sensitive and rapid screening method for Ralstonia solanacearum is critical for the control of tobacco wilt. In the present study, tissue homogenates of three tobacco varieties (Honda, Yunnan 87 and K326) with different resistance to R. solanacearum, were individually used as additives to the bacteria culture medium. The changes in R. solanacearum secretome were investigated and one of the most abundant secretary proteins with increased expression, polygalacturonase (PG), was selected as a marker for R. solanacearum identification. Then PG gene was cloned into E. coli, and the expressed protein was used as the immunogen to develop monoclonal antibodies. Subsequently, the monoclonal antibody against PG was coupled with synthesized polystyrene microspheres, and a rapid test strip system was developed for the detection of R. solanacearum based on time-resolved fluorescent immunochromatographic (TRFIC) method. Under optimal conditions, the detection limit of the strips could reach 72 cells/mL; while it was 422 cells/mL with a linear range from 4 × 10² to 5.12 × 10⁴ cells/mL when testing tobacco samples, which is 1000 times lower than that of colloidal gold-labeled strips. Notably, no cross-reactivity was observed with nine tobacco-related pathogens. Finally, this TRFIC strips was applied to detect R. solanacearum existed in the tobacco and soils of fields with or without bacterial wilt. The results demonstrated that this TRFIC strips could distinguish the difference in bacterial concentration existed in tobacco and soil between the two fields. In summary, this test strip is suitable for sensitive, quick screening of R. solanacearum in tobacco.

AIEgens enabled ultrasensitive point-of-care test for multiple targets of food safety: Aflatoxin B1 and cyclopiazonic acid as an example

Food safety is currently a significant issue for human life and health. Various fluorescent nanomaterials have been applied in the point-of-care test (POCT) for food safety as labeling materials. However, previous fluorescent nanomaterials can cause aggregation-caused quenching (ACQ), thus reducing the detection sensitivity. Conversely, aggregation-induced emission luminogens (AIEgens) are promising candidates for POCT in the food safety field because they can enhance detection sensitivity and throughput. Mycotoxins, such as aflatoxin B1 (AFB1) and cyclopiazonic acid (CPA), are a primary threat to human life and health and a significant food safety issue, and their on-site detection from farm to table is needed. Herein, an ultrasensitive point-of-care test was developed based on TPE-Br, a blue-emissive tetraphenylethylene derivative AIEgen. Under optimal conditions, this AIEgen-based lateral-flow biosensor (ALFB) allowed for a rapid response of 8 min toward AFB1 and CPA detection, with considerable sensitivities of 0.003 and 0.01 ng/mL in peanut matrices, respectively. In peanut matrices, the recoveries were 90.3%-110.0% for both mycotoxins, with relative standard deviations (RSDs) below 6%. The ALFB was further validated via UPLC-MS/MS using spiked peanut samples. AIEgens open an avenue for on-site, ultrasensitive, high-throughput detection methods and can be extensively used in point-of-care tests in food safety.