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Background Immunochromatographic test strip (ICTS) has become one of the most widely used rapid diagnostics platforms for the point-of-care testing of various contaminant residues in food. However, traditional gold nanoparticle (AuNP)-based ICTSs suffer limited sensitivity ranged from ng/mL to μg/mL, thus severely hindering them from meeting the increasing demand for trace target detection. Scope and approach The use of novel nanomaterials with high signal strength to replace AuNPs as signal probes is considered as the most effective strategy to enhance the sensitivity of ICTS nanosensor. Among them, highly luminescent nanomaterials have attracted increasing interest in improving the detection performance of ICTS due to its advantages of visualization, quantitation, multiplexing, anti-jamming capability, and high sensitivity. Currently available nanomaterials include dye-based fluorescent nanomaterials, semiconductor quantum dots and its nanobeads, up-conversion nanoparticles, time-resolved fluorescence nanomaterials, aggregation-induced emission nanomaterials, noble metal nanoclusters, and magnetic fluorescent nanomaterials, and they have been successfully applied for detecting various hazardous substances, including pesticide and veterinary drug residues, food additives, mycotoxins, heavy metal ions, allergens, and microorganisms. In this review, thus we comprehensively summarize the application potentials and critical roles of such nanomaterials as signal reporters in current ICTS systems to ensure food safety. Key findings and conclusions A detailed classification of signal probes with emphasis on the inherent advantage, synthesis, signal amplification strategy, and further improvement of each luminescent nanomaterial was discussed and the state-of-the-art of commercial fluorescent ICTS kits and readers for food safety was summarized. Further improvement should focus on the design and development of high-quality luminescent nanomaterials, ultra-sensitive detection, multiplexing and multimode sensing, accurate quantification, and intelligent signal reading.

The most of embryo losses occur before the day 16 after artificial insemination, but there is no low cost and easy operation that can detect pregnancy with high accuracy within three weeks post-insemination in cattle. In this study, blood samples were collected at day 18 of the estrous cycle, and days 18, 25 and 35 of pregnancy, and relative levels of interferon stimulated genes (ISGs), Toll-like receptor (TLRs), complement components, early pregnancy factor (EPF) and pregnancy-associated plasma protein A (PAPPA) proteins were analyzed through Western blot. In addition, a colloidal gold immunochromatographic test strip was developed using the selected antibody, and the test was used for early pregnancy diagnosis. The results showed that there were changes in relative levels of plasma ISGs, TLRs, complement components, EPF and PAPPA proteins during early pregnancy in cattle, and complement component 1q (C1q) could be used as an ideal marker to develop a colloidal gold immunochromatographic test strip for early pregnancy diagnosis. In addition, the accuracy of pregnancy diagnosis by this test strip was 91.67% (11/12) for pregnant cows and 80% (8/10) nonpregnant cows at day 18 after insemination. In conclusion, the changes in plasma ISGs, TLRs, complement components, EPF and PAPPA proteins may be related to the maternal systemic immune modulation during early pregnancy, and a colloidal gold immunochromatographic test strip was developed for early pregnancy diagnosis using C1q as the ideal marker in cows. However, this colloidal gold immunochromatographic test strip needs further studies to improve the accuracy.

A variety of methods have been reported using polymerase chain reaction (PCR)-based nucleic acid testing (NAT) because of its potential to be used in highly sensitive inspection systems. Among these NATs, fusion-PCR (also called as overlap-extension-PCR) has been focused on this study and adopted to generate the fused amplicon composed of plural marker gene fragments for detection. Generally, conventional agarose gel electrophoresis followed by gel staining is employed to check the PCR results. However, these are time-consuming processes that use specific equipment. To overcome these disadvantages, the immunochromatographic test (ICT) for the detection of PCR amplicons with hapten-labels that were generated by PCR using hapten-labeled primers was also adopted in this study. Based on these concepts, we constructed the systems of hapten-labeled fusion-PCR (HL-FuPCR) followed by ICT (HL-FuPCR-ICT) for the two and three marker genes derived from pathogenic microbe. As a result, we successfully developed a two marker genes system for the pathogenic influenza A virus and a three marker genes system for the penicillin-resistant Streptococcus pneumoniae. These detection systems of HL-FuPCR-ICT are characterized by simple handling and rapid detection within few minutes, and also showed the results as clear lines. Thus, the HL-FuPCR-ICT system introduced in this study has potential for use as a user-friendly inspection tool with the advantages especially in the detection of specific strains or groups expressing the characteristic phenotype(s) such as antibiotic resistance and/or high pathogenicity even in the same species.

Chronic pulmonary aspergillosis (CPA) is an infection of the lung usually caused by Aspergillus fumigatus in patients with pre-existing pulmonary diseases. Its diagnosis hinges on demonstrating IgG antibodies against A. fumigatus. Herein, we evaluated the performance of a newly introduced point of care test (POCT) kit, the LDBio Aspergillus IgG/IgM lateral flow assay (LFA) in India with the standard ImmunoCAP kit for diagnosing CPA.A total of 60 serum samples (30 CPA cases and 30 controls) were evaluated by the Aspergillus immunochromatographic test (ICT) IgG/IgM LFA. Fluorescent-enzyme immunoassay was used to determine specific A. fumigatus-IgG concentrations (positive27 mgA/L). Further, a systematic review and meta-analysis of studies (up to August 26, 2021) reporting the performance of LDBio ICT for the diagnosis of CPA was performed.A sensitivity of 86.7%, specificity of 90%, negative predictive value of 87.1%, positive predictive value of 89.7%, negative likelihood ratio of 0.15, positive likelihood ratio of 8.67, and was observed for the LDBio IC. There was good agreement between LDBio ICT and ImmunoCAP (88.3%) with a Cohen's Kappa score of 0.77. Our systematic review identified four studies and the pooled sensitivity of 90%, specificity of 91%, area under the curve of 0.94 and diagnostic odds ratio of 57.2, for CPA diagnosis by LDBio ICT.Aspergillus LDBio ICT assay exhibits good sensitivity and can be used to screen CPA cases.

One of the major concerns in the application of nanocarriers in biosensing is the impair of the recognition molecules bioactivity loaded on their surfaces due to harsh and laborious cross-linking and random orientation, resulting in unsatisfactory sensitivity. Herein, we proposed a novel immunochromatographic test strip (FNS-ag-DICTS) by taking advantage of the antigen (ag) modified Fe2O3 nanostructures (FNSs) as new signal tags and goat anti-mouse IgG labeling on the detection line instead of ag, which was used for sensitive detection of aflatoxin B1 (AFB1). The fabricated FNS-ag can orientate the Fab region of monoclonal antibodies (mAbs), waiving the intrinsic limitations of traditional nanomaterials labeled mAbs. Under optimal conditions, FNS-ag-DICTS possessed excellent specificity and a wide detection range, with a visual limit of detection (vLOD) of 0.0125 ng mL−1. In addition, the biosensor successfully detected AFB1 in peanut, green bean and corn, with an average recovery rate of 82.8–124.9%.

To improve viral antibody detection and disease control, laboratories need faster and simpler methods for direct detection of H9AIV in clinical samples. In this study, test strips were developed for rapid detection of H9AIV antibodies in poultry serum by a sandwich method with double-line detection. The hemagglutinin protein was labeled with colloidal gold as a detection reagent and was blotted on the test lines, while goat anti-rabbit IgG was utilized on the control line of the nitrocellulose membrane. The test strips have high specificity, sensitivity, and stability, with a correlation coefficient of 0.9656 and coefficients of variation below 10%. Application of the kit to quantitative detection of H9AIV antibodies in 504 samples collected from chickens showed a coincidence rate of 80.56% with previously run HI assays.

In dogs, canine parvovirus (CPV) enteritis is associated with high morbidity and fatality rates requiring early diagnosis to facilitate treatment and reduce its spread. In recent times, various commercial immunochromatographic (IC) test kits are available for its rapid diagnosis, which require an assessment of their accuracy. Therefore, precision of a point-of-care IC combination test kit for canine coronavirus (CCoV)/CPV faecal antigen detection was evaluated in this study. Multicentred random faecal samples from 115 dogs with gastroenteritis were checked for the presence of CPV antigens using the SensPERT IC combination test kit and the result was compared with polymerase chain reaction (PCR) as a reference test. Parvovirus was detected in 105 (91.3%) and 108 (93.9%) faecal samples by the point-of-care test kit and PCR, respectively. The point-of-care IC test kit showed 95.4% relative sensitivity, 71.4% specificity, 98.1% positive predictive value, 50.0% negative predictive value, and 93.9% accuracy comparable to conventional PCR in the samples tested. This point-of-care test kit also demonstrated a fair positive likelihood ratio (3.34), a very low negative likelihood ratio (0.07) and a moderate agreement (Kappa = 0.6) compared with conventional PCR. This test kit has shown to be very useful in the screening of dogs for CPV infection, and is a reliable alternative for diagnosing CPV both in conventional laboratories and remote areas without laboratories. Negative results in the IC testing with high suspicion of CPV infection should be further confirmed using superior test such as PCR.

Outbreaks of Salmonella infections have always attracted world-wide attention in food industry. Therefore, it is particularly important to detect Salmonella. In this study, we aimed to develop a rapid, simple, sensitive, and broad-spectrum colloidal gold immunochromatographic test strip (ICTS) for detecting Salmonella. The prepared monoclonal antibody (mAb) 1B4 was labeled with colloidal gold and used as the capture antibody, as it can pair with itself to form a sandwich detection platform. The sensitivity of the test strip for Salmonella typhimurium was 4 × 105 CFU/mL with naked eye and the pathogen was detected in 5–15 min. The colloidal gold ICTS can be used to detect 18 stains of Salmonella and there was no cross-reaction with 14 other food-borne pathogens. Salmonella typhimurium, Salmonella paratyphi B, and Salmonella enterica in chicken were detected after 7 h, 7 h and 6 h of incubation, respectively, and the detection limit was as low as 1 CFU/mL. In short, this is important reports of colloidal gold ICTS for detecting so many stains of Salmonella, and this will be a huge improvement for detecting multiple Salmonella in food samples.

By using well-designed magnetic nanocomposites (MNCs) as probes, immunochromatographic test strip (ICTS) has shown some advantages in sensitivity and quantification of in vitro detection methods. In this study, MNCs were modified with controllable surface carboxyl groups through a facile two-step approach. 3-aminopropyltrimethoxysilane (APTS) was firstly grafted onto MNCs by a sol-gel reaction, followed by amide reaction between amino group of APTS and succinic anhydride. Density of controllable groups and conformation on the surface of MNCs were tuned by adjusting the APTS-to-MNCs ratio. Vibrio parahaemolyticus (VP) was used to examine the effect of surface modification of MNCs on the antibody conjugation and detection performance in ICTS. We also proposed the underlying mechanism based on the AFM analyses of antibody conjugation on two typical functionalized MNCs. It was found that with the increasing of APTS input, lower APTS-to-MNCs ratios (0.03 and 0.3 μL/mg) can improve surface carboxylic groups’ density of MNCs. The optimal APTS-to-MNCs ratio (3 μL/mg) promoted 1.4-fold antibody conjugating efficiency, and 3.4-fold signal-to-noise value in the ICTS for 2 × 10 5 CFU/mL VP as compared with the ratio of 0.03 μL/mg. Whereas, due to the steric hindrance, the antibody conjugating efficiency and signal-to-noise value at high APTS-to-MNCs ratio (12 μL/mg) respectively decreased 13.9% and 74.7% than the optimal ratio. Accordingly, the controlled surface functionalization of MNCs is the key for highly efficient and sensitive ICTS.

Over 90% of schistosomiasis infections occur in sub-Saharan Africa. A rapid ICT test would be a cheap and easy tool that could be used also in the field. We preliminarily evaluated the performance of a new Schistosoma black-latex based IgG-IgM ICT (Black-ICT) on serum samples. The results indicate a high sensitivity (98.0%) but the specificity depends on the application of a cut-off value that can discriminate between positive and negative samples. Considering a possible direct application of this test on blood from finger prick, the results are promising, providied that a signal intensity scale is developed, guiding the result interpretation.

Immunochromatographic test strip (ITS) for point-of-care testing (POCT) has attracted prominent attention due to the advantages including rapid response, low cost and good portability. Here, we developed a sensitive ITS for detecting aflatoxin B1 (AFB1) by using dendritic platinum nanoparticles (DPNs) as novel pressure/colorimetric dual-readout probes. DPNs-labeled antibody of AFB1 were used as the signal tracer of the immunochromatographic process. After 10-min competitive immunoreaction, black color appeared on the test line of ITS due to the accumulation of DPNs, which was observed visually as a colorimetric readout for qualitation purpose. Furthermore, DPNs with peroxidase-like activity caused decomposition of hydrogen peroxide aqueous solution to produce pressure change signal in vials, which was detected by a hand-held pressure meter for quantitation purpose. With the pressure readout mode, the detection range was 0.05–10 ng mL−1, and the detection limit was 0.03 ng mL−1 (S/N = 3) for AFB1. The proposed ITS was successfully utilized for detecting AFB1 in herbal medicine samples, and the acceptable recoveries of 93.77–114.09% indicated the reliability for real sample detection. It provides a new avenue for POCT with great application potential in various area including drug and food quality control, pollutants monitoring as well as medical diagnosis.