African Swine Fever (ASF), caused by the African swine fever virus (ASFV), has inflicted significant economic losses on the pig industry in China. The key to mitigating its impact lies in accurate screening and strict biosecurity measures. In this regard, the development of colloidal gold immunochromatographic test strips (CGITS) has proven to be an effective method for detecting ASFV antibodies. These test strips are based on the ASFV p30 recombinant protein and corresponding monoclonal antibodies. The design of the test strip incorporates a high-concentration colloidal gold-labeled p30 recombinant protein as the detection sensor, utilizing Staphylococcal Protein A (SPA) as the test line (T line), and p30 monoclonal antibody as the control line (C line). The sensitivity and specificity of the test strip were evaluated after optimizing the labeling concentration, pH, and protein dosage. The research findings revealed that the optimal colloidal gold labeling concentration was 0.05 %, the optimal pH was 8.4, and the optimal protein dosage was 10 μg/mL. Under these conditions, the CGITS demonstrated a detection limit of 1:512 dilution of ASFV standard positive serum, without exhibiting cross-reactivity with antibodies against other viral pathogens. Furthermore, the test strips remained stable for up to 20 days when stored at 50 °C and 4 °C. Comparatively, the CGITS outperformed commercial ELISA kits, displaying a sensitivity of 90.9 % and a specificity of 96.2 %. Subsequently, 108 clinical sera were tested to assess its performance. The data showed that the coincidence rate between the CGITS and ELISA was 93.5 %. In conclusion, the rapid colloidal gold test strip provides an efficient and reliable screening tool for on-site clinical detection of ASF in China. Its accuracy, stability, and simplicity make it a valuable asset in combating the spread of ASF and limiting its impact on the pig industry.

The rapid and accurate determination of triadimenol residues is of great significance. In this study, based on the advantages of high efficiency, rapidity, reliability, simplicity and low cost of immunology, a test strip product for the rapid detection of triadimenol residues in tobacco was designed based on the optimization of conditions such as pH and dosage of diluent, concentration of antibody stock solution, type of confining solution and complex solution, with high specificity, accuracy and The results of 20 samples of fresh and first roasted tobacco were all consistent with the method of gas chromatography, which proved the reliability of the test strips. The detection limit for fresh and roasted tobacco was 5 mg/kg, and the test strips developed in this study are suitable for mass testing of tobacco samples in tobacco-related laboratories because of their short detection time, simple pre-treatment and detection methods, and good application prospects.

In this study, the establishment of a colloidal gold immunochromatographic method for the detection of cypermethrin in tobacco was achieved by using colloidal gold immunochromatography: strong specificity and high sensitivity of cypermethrin semi-antigens and encapsulants were prepared during the study. The best colloidal gold solution was prepared by spectrophotometer and transmission electron microscope screening; the preparation process of gold-labeled antibodies was optimized, and finally the product of colloidal gold rapid detection test strips for cypermethrin was developed. The results of technical parameters and detection indexes showed that the detection limit of cypermethrin in tobacco was 1 mg/kg, and there was no cross-reaction with bifenthrin, cypermethrin, cyfluthrin and phenothrin, and the detection results of 30 tobacco samples were consistent with those of gas chromatography.

Influenza A epidemics, which occur annually in varying degrees worldwide, is a global challenge to healthcare facilities owing to several limitations of the current detection methods. Therefore, the development of a rapid, convenient, and economical method for the early diagnosis of influenza A will aid clinical treatment and epidemic control. Currently, most of the commonly used clinical rapid tests utilize colloidal gold test strips that detect specific influenza virus antigens but are limited by low sensitivity. Therefore, this study combined catalytic hairpin assembly (CHA) with colloidal gold immunochromatographic assay (GICA) to develop a highly sensitive and visual CHA-GICA test strip. Clinical sample analysis revealed that the sensitivity of the assay was 81.8% and 74% under optimal (35 °C) and room temperature (25 °C) conditions, respectively. In conclusion, this study developed a rapid nucleic acid assay for detecting influenza A virus with high sensitivity and specificity, which can improve the clinical detection of influenza A.

OBJECTIVE: The presence of tetracycline (TC) and its residues in raw milk and milk dairy products poses a threat to human health due to the induction of antibiotic resistance of bacteria that can be transmitted between animals, humans, and the environment. The aim of this study was to investigate the transfer of TC from raw milk to different dairy products: pasteurized milk, boiled milk, sour milk, skimmed milk, and cottage cheese. We analyzed samples of milk from different sources: household farmers, local farms, and milk factories.
METHODS: The analyses of TC in milk and dairy products were performed using colloidal gold immunochromatography assay (GICA) and enzyme-linked immunosorbent assay (ELISA).
RESULTS: The highest content of TC was found in the milk purchased from local household farmers; therefore, these samples were chosen for the study of TC transfer to dairy products. TC was also found in sour milk at levels comparable with those obtained in raw milk. The average TC content decreased following heat treatment of the milk, as follows: for pasteurized milk 22.07% and for boiled milk 29.35%. The highest concentrations were determined in cottage cheese in the range 200-620 μg/kg.
CONCLUSIONS: TC residues are transferred from milk to dairy products in various amounts depending on the preparation conditions, and due to their chemical properties, they accumulate in concentrated derivatives, such as cheese. Therefore, TC can be identified even in cheeses prepared from milk with undetected antibiotic levels.

Bovine parvovirus (BPV) is a pathogen responsible for respiratory and digestive tract symptoms in calves and abortion and stillbirth in pregnant cows. In this study, we developed a colloidal gold immunochromatographic (GICG) strip with an enhanced signal for detecting BPV according to the double-antibody sandwich principle and an enzyme-based signal amplification system to amplify the signal. This system utilizes horseradish peroxidase reacting with a substrate solution containing 3,3\',5,5\'-tetramethylbenzidine and dextran sulfate to obtain insoluble blue products on the test and control lines. We optimized different reaction conditions, including the amount of monoclonal antibodies (mAbs), pH of the colloidal gold solution, coating solution, blocking solution, sample pad treatment solution, antibody concentration in the control line, and antibody concentration in the detection line. The sensitivity of the signal-enhanced GICG strip showed that the minimum amount for detecting BPV was 102 TCID50, 10 times higher than that of the traditional GICG strip. The results of the specificity test showed that the signal-enhanced GICG strip had no cross-reactivity with BRV, BVDV, or BRSV. The results of the repeatability test showed that the coefficient of variation between and within batches was less than 5%, showing good repeatability. Moreover, for validation, PCR and the signal-enhanced GICG strip were used to detect 280 clinical bovine fecal samples. The concordance rate compared with PCR was 99.29%. Hence, the developed strip exhibited high sensitivity and specificity for the detection of BPV. Therefore, this strip could be a rapid, convenient, and effective method for the diagnosis of BPV infection in the field.

BACKGROUND: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread around the world, caused millions of deaths and a severe illness which poses a serious threat to human health.
OBJECTIVE: To develop an antigen detection kit that can identify Omicron novel coronavirus mutants.
METHODS: BALB/c mice were immunized with the nucleocapsid protein of SARS-CoV-2 Omicron mutant treated with β-propiolactone. After fusion of myeloma cells with immune cells, Elisa was used to screen the cell lines capable of producing monoclonal antibodies. The detection kit was prepared by colloidal gold immunochromatography. Finally, the sensitivity, specificity and anti-interference of the kit were evaluated by simulating positive samples.
RESULTS: The sensitivity of the SARS-CoV-2 antigen detection kit can reach 62.5 TCID50/mL, and it has good inclusiveness for different SARS-CoV-2 strains. The kit had no cross-reaction with common respiratory pathogens, and its sensitivity was still not affected under the action of different concentrations of interferences, indicating that it had good specificity and stability.
CONCLUSIONS: In this study, monoclonal antibodies with high specificity to the N protein of the Omicron mutant strain were obtained by monoclonal antibody screening technology. Colloidal gold immunochromatography technology was used to prepare an antigen detection kit with high sensitivity to detect and identify the mutant Omicron strain.

The common carbamate insecticide aldicarb is considered one of the most acutely toxic pesticides. Herein, rational design was used to synthesize two haptens with spacers of different carbon chain lengths. The haptens were then used to immunize mice. The antibodies obtained were evaluated systematically, and a colloidal gold immunochromatographic strip was developed based on an anti-aldicarb monoclonal antibody. The 50% inhibition concentration and linear range of anti-aldicarb monoclonal antibody immunized with Hapten 1 were 0.432 ng/mL and 0.106-1.757 ng/mL, respectively. The cross-reactivities for analogs of aldicarb were all <1%. The limit of detection of the colloidal gold immunochromatographic strip was 30 μg/kg, and the average recoveries of aldicarb ranged from 80.4 to 110.5% in spiked samples. In the analysis of spiked samples, the test strip could accurately identify positive samples detected by the instrumental method in the GB 23200.112-2018 standard but produced some false positives for negative samples. This assay provides a rapid and accurate preliminary screening method for the determination of aldicarb in agricultural products and environments.

The coronavirus disease 2019 (COVID-19) is outbreaking all over the world. To help fight this disease, it is necessary to establish an effective and rapid detection method. The nucleocapsid (N) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is involved in viral replication, assembly, and immune regulation and plays an important role in the viral life cycle. Moreover, the N protein also could be a diagnostic factor and potential drug target. Therefore, by synthesizing the N gene sequence of SARS-CoV-2, constructing the pET-28a (+)-N recombinant plasmid, we expressed the N protein in Escherichia coli and obtained 15 monoclonal antibody (mAbs) against SARS-CoV-2-N protein by the hybridomas and ascites, then an immunochromatographic test strip method detecting N antigen was established. In this study, we obtained 14 high-titer and high-specificity monoclonal antibodies, and the test strips exclusively react with the SARS-CoV-2-N protein and no cross-reactivity with other coronavirus and also recognize the recombinant N protein of Delta (B.1.617.2) variant. These mAbs can be used for the early and rapid diagnosis of SARS-CoV-2 infection through serological antigen.

BACKGROUND: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread rapidly to 185 regions and countries around the world with more than 2.8 million confirmed infections and 203,044 deaths. Respiratory diseases caused by SARS-CoV-2 are serious threats to human health.
OBJECTIVE: To develop a rapid detection kit for new coronavirus antibodies and use it to study the dynamic changes in antibodies in clinically confirmed SARS-CoV-2-infected patients.
METHODS: The SARS-CoV-2 IgM/IgG antibody test kit (colloidal gold method) was developed. Serum SARS-CoV-2 IgM and IgG antibodies were tested in SARS-CoV-2- and non-SARS-CoV-2-infected persons, respectively.
CONCLUSIONS: The sensitivities of the SARS-CoV-2 IgM/IgG antibody test kit (colloidal gold method) were 50%, 70%, 92.5% and 97.5% after 1-3 days, 4-6 days, 7-9 days and >9 days of admission, respectively, and the specificities of the IgM, IgG and IgM + IgG antibodies were all 100%. Using the SARS-CoV-2 IgM/IgG antibody test kit (colloidal gold method), the positive rates of SARS-CoV-2 IgM and IgG antibodies increased from 50% to 92.5% after 1-3 days, 4-6 days and 7-9 days of admission, which showed an increasing trend. The titers of the SARS-CoV-2 IgM and IgG antibodies in the positive specimens increased with the length of admission.