Gold Immunochromatographic Assay Research Articles

Rapid and sensitive detection of flubendiamide in grapes and tomatoes using a colloidal gold immunochromatography assay

In this study, we developed a monoclonal antibody (mAb)-based colloidal gold immunochromatography assay (CG-ICA) strip for the rapid and sensitive detection of flubendiamide (FBD) in food samples. Our anti-FBD mAb 2B1 was highly specific and had a half-maximal inhibitory concentration (IC50) of 1.55 ng/mL under optimal conditions. It belongs to the IgG2a isotype and has a Kaff value of 1.52 × 109 mol/L. The strip provided a visual detection limit of 50 ng/g for both grapes and tomatoes, with a cut-off value of 1,000 ng/g and these qualitative results were observed within 15 min. For quantitative analysis, the calculated detection limits were 6 ng/g and 5 ng/g in grapes and tomatoes, respectively. The average recoveries of FBD ranged from 88.8% to 111.8% in grapes and 94.5% to 110.6% in tomatoes. The proposed strip assay is highly practical for screening FDB in food samples.

Convalescent Plasma for COVID-19: A Single Center Prospective Experience with Serial Antibody Measurements and Review of the Literature.

Background: High-titer convalescent plasma given early for COVID-19 may decrease progression into a severe infection. Here, we reported a study of serial antibody measurements in patients who received CP at our center and performed a systematic review of randomized trials on CP. Methods: Our center participated in the Mayo Clinic Expanded Access Program for COVID-19 Convalescent Plasma. Patients diagnosed with COVID-19 by nasopharyngeal polymerase chain reaction at our center between April and August 2020 were included in the study if staffing was available for specimen collection. Through a colloidal gold immunochromatography assay, these patients’ IgM and IgG antibody responses were measured at baseline (Day 0) and after transfusion (Day 1, 2, etc.). Donor CP antibody levels were measured as well. Results: 110 serum specimens were obtained from 21 COVID-19 patients, 16 of whom received CP. The median time from developing symptoms to receiving CP was 11 days (range 4–21). In 9 of 14 (64%) cases where both recipient and donor CP antibody levels were tested, donor COVID-19 IgG was lower than that of the recipient. Higher donor antibody levels compared with the recipient (R = 0.71, p < 0.01) and low patient IgG before CP transfusion (p = 0.0108) correlated with increasing patient IgG levels from baseline to Day 1. Among all patients, an increased COVID-19 IgG in the short-term and longitudinally was positively correlated with improved clinical outcomes (ρ = 0.69, p = 0.003 and ρ = 0.58, p < 0.006, respectively). Conclusions: In a real-world setting where donor CP was not screened for the presence of antibodies, CP in donors might have less COVID-19 IgG than in recipients. An increase in patient antibody levels in the short term and longitudinally was associated with improved clinical outcomes.

Gold immunochromatographic strip assay for the detection of triamcinolone acetonide and budesonide in milk

A monoclonal antibody against triamcinolone acetonide (TCA) and budesonide (BUD) was prepared using a hapten that was generated by introducing a carboxyl group into the structure of TCA. Based on the prepared monoclonal antibody, a gold nanoparticle-based lateral-flow immunoassay (GLFA) was developed with the ability to screen TCA and BUD in milk. The visible limits of detection of the GLFA for the analysis of TCA and BUD were 0.1 and 0.5 ng/mL with a cutoff value of 5 and 10 ng/mL, respectively, in milk. Average recoveries of TCA and BUD in milk were 92.0–102.2% and 96.0–98.8% with a good correlation between the results from the GLFA and LC-MS/MS analysis. These results demonstrated that the GLFA method for the rapid detection of TCA and BUD in milk samples is reliable and sensitive.

International multi-center evaluation of a rapid antigen test based on gold immunochromatographic assay for detection of severe acute respiratory syndrome coronavirus 2

Objective: The gold immunochromatographic assay for detection of SARS-CoV-2 antigen was evaluated by international multi-center clinical trial. Methods: A total of 1 855 clinical parallel samples with valid test results (for nucleic acid and antigen tests, respectively) were collected from nine countries, including Germany, the United Kingdom, Ukraine, France, India, Thailand, Malaysia, the United States of America and Brazil, with sampling period from January 3, 2021 to September 22, 2021. These samples were detected by SARS-CoV-2 antigen test kit (colloidal gold immunochromatography assay) and nucleic acid detection kit (real-time fluorescent quantitative reverse transcription polymerase chain reaction). Positive coincidence rates [(number of antigen-positive cases/nucleic acid-positive cases)×100%], negative coincidence rates [(number of antigen-negative cases/nucleic acid-negative cases)×100%], total coincidence rates [(number of cases with consistent results for both antigen and nucleic acid detection/number of total cases) ×100%], as well as Kappa values were calculated. The differences of the above indictors among different countries were evaluated by the coefficient of variation. The detection rates of the antigen test for samples with different cycle threshold values (Ct values) for the nucleic acid detection, different characteristics and different mutant strains were analyzed. Results: For all samples, the positive, negative, and total coincidence rate between the antigen test and nucleic acid assay was 90.8% (569/627), 99.7% (1 224/1 228) and 96.7% (1 793/1 855), respectively, and the consistency coefficient Kappa value was 0.924. Among these countries, the coefficient of variation for positive coincidence rates (except for Malaysia with a lot of samples with Ct value>30), negative coincidence rates (except for France without negative samples) and total coincidence rates (except for France) was 6%,<1%, and 6%, respectively. When Ct values were less than 25, the detection rates of antigen test were 83.3%-100% for each countries (the coefficient of variation was 6%); The total detection rate and the coefficient of variation was 93.4% (428/458) and 5%, respectively, for asymptomatic infected persons and cases within 7 days post onset of symptoms; the total detection rate for various SARS-CoV-2 mutant strains was 97.5% (119/122); and it showed negative results for samples from cases infected with other viruses, including influenza A virus subtype H1N1, influenza B virus, respiratory syncytial virus subgroups A and B, coxsackievirus 16, human metapneumovirus, parainfluenza virus types 1 and 4, Epstein-Barr virus and adenovirus. Conclusion: The SARS-CoV-2 antigen test kit showed excellent authenticity, and there were few differences for its indictors among nine countries, therefore it can meet the needs of large-scale early screening of SARS-CoV-2 infection.

A monoclonal antibody-based colloidal gold immunochromatographic strip for the analysis of novobiocin in beef and chicken

In this study, a monoclonal antibody (mAb) 1G5 against novobiocin with high sensitivity and specificity was prepared from a newly-designed hapten. According to the results of an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA), the 50%-inhibitory concentration of the anti-novobiocin mAb was 6.9 ng/mL and the cross-reactivity was less than 0.1% to its analogues. Furthermore, a rapid colloidal gold immunochromatographic assay (ICA) was successfully developed for the determination of novobiocin in spiked samples. Two calibration curves were established respectively, for beef and chicken samples. The ICA results showed a visual colorimetric value of 50 ng/mL and a cut-off value of 300 ng/mL in beef samples. The ICA results of chicken samples were almost the same as that of beef. When quantitative detection was performed using a strip reader, the detection ranges for quantitative analysis in beef and chicken were 23.7–287.5 and 19.7–263.8 µg/kg respectively. Recoveries were between 82.7 and 95.3% for beef samples with the coefficient of variation (CV) ranging from 2.5 to 5.1%. Recoveries were in the range of 89.6–105.5% with the CV ranging from 2.9% to 6.3% for chicken samples. Importantly, these results from the ICA were highly consistent with the results obtained by LC-MS/MS. Therefore, this ICA could be used as an alternative means for the rapid determination of NOV in a large number of beef and chicken samples.

Development of a colloidal gold immunochromatographic strip for the rapid detection of pefloxacin in grass carp with a novel pretreatment method

A rapid colloidal gold immunochromatography assay (GICA) for the detection of pefloxacin (PEF) was established and optimized. The anti-PEF monoclonal antibody (mAb) was used to target PEF as a colloidal gold-mAb conjugate. The mAb belonged to the IgG2b subtype, lambda light chain, the affinity constant (Ka) was 5.21 × 109 L·mol−1, and its half maximal inhibitory concentration (IC50) was 0.23 ng·mL−1. No obvious cross-reactivity (CR) was observed with other common fluoroquinolone antibiotics, including ciprofloxacin (CIP), norfloxacin (NOR), lomefloxacin (LOM) and ofloxacin (OFL). The visual limit of detection (vLOD) of the optimized GICA was 2 ng·g−1 under the conventional pretreatment method, and the assay was completed in 15 min. Liquid chromatography tandem-mass spectrometry (LC–MS/MS) was employed to confirm the performance of the strip. In addition, a novel pretreatment was established and compared with conventional pretreatment. Without the removal of organic solvents, the novel pretreatment method reduced the sample pretreatment time (more than 10 min). The vLOD of the optimized GICA was also 2 ng·g−1 when applying the novel pretreatment method. In conclusion, the proposed PEF-GICA could detect samples containing PEF rapidly and accurately, and the novel pretreatment method saved the time of sample pretreatment and improved the efficiency of detection.

A Novel Full-length IgG Recombinant Antibody Highly Specific to Clothianidin and Its Application in Immunochromatographic Assay.

The toxicity of clothianidin to non-target organisms has gradually attracted world-wide attention. It is essential to develop reliable methods for the on-site detection of clothianidin residue. In this study, analogue-based heterologous ic-ELISAs were designed to rapidly screen desirable hybridomas, which could be used for the construction of recombinant antibodies (RAbs) against clothianidin. Based on the antibody variable region genes, two full-length IgG RAbs (1F7-RAb and 5C3-RAb) were produced by the mammalian cell expression system. The performance of the two RAbs was characterized and compared by heterologous ic-ELISAs and non-competitive surface plasmon resonance (SPR) assays. Using heterologous ic-ELISAs, the 1F7-RAb exhibited highly specific and sensitive recognition to clothianidin with an IC50 of 4.62 μg/L, whereas the 5C3-RAb could bind to both clothianidin and dinotefuran. The results of the non-competitive SPR assay further verified that the 1F7-RAb had a higher specificity and affinity to clothianidin than the 5C3-RAb. Finally, a gold immunochromatographic assay based on the novel antibody, 1F7-RAb, was developed for rapid detection of clothianidin with high sensitivity (visual detection limit of 2.5 μg/L), specificity, and good reproducibility, which can be used as an effective supervision tool for clothianidin residue in agricultural and environmental samples.

Gold‐based paper sensor for sensitive detection of procalcitonin in clinical samples

Procalcitonin (PCT) has been considered as an important biomarker of bacterial infections. An accurate monitoring of serum PCT is meaningful in sepsis diagnosis and antibiotic guidance. Here, monoclonal antibodies (mAbs) against human PCT were prepared using recombinant PCT (rPCT) protein as immunogen. The combination of mAbs 3G9 and 9G10, which were selected as capture and detection antibodies, respectively, presented the best performance in pairwise analysis. Based on the paired mAbs, a gold immunochromatographic assay (GICA) for PCT analysis was developed in serum samples, with a visible limit of detection of 0.1 ng/mL and a linear detection range of 0.49–13.90 ng/mL. There was an adequate correlation between GICA and clinical data. Therefore, our developed GICA has great potential for the rapid and sensitive determination of PCT in clinical practice.

Rapid colloidal gold immunochromatographic assay for the detection of SARS-CoV-2 total antibodies after vaccination.

An epidemic caused by the severe acute respiratory syndrome coronavirus (SARS-CoV-2) spread globally in just a few months. To prevent the further spread of the virus, millions of people around the world have been vaccinated for COVID-19. Although the plaque reduction neutralization test (PRNT) has become the gold standard method for determining neutralizing antibodies, this method has many limitations; therefore, there remains an urgent need for a quick and accurate technique to evaluate the immune efficacy of COVID-19 vaccines. Here, after the recombinant expression of the SARS-CoV-2 spike protein receptor binding domain (S-RBD), we established a colloidal gold immunochromatographic assay (GICA) based on the principle of a double antigen sandwich for the detection of total antibodies in sera. Under the developed conditions, the GICA was capable of the rapid detection of SARS-CoV-2 total antibodies within 15 min. In addition, the anti-S-RBD antibodies measured by the GICA had a good correlation with the results measured by ELISA, indicating that the GICA may be used as a rapid tool for the detection of neutralizing antibodies derived from SARS-CoV-2 infection. Clinical detection was performed using serum samples obtained from 40 subjects who had received their two doses of the COVID-19 vaccine and 20 unvaccinated serum samples. We found that our method had high sensitivity and specificity; therefore, our convenient and rapid GICA method could preliminarily evaluate the protection rate and effectiveness of vaccines by monitoring total antibody levels.

A colloidal gold immunochromatographic strip assay for the rapid detection of Shigella in milk and meat products

Anti-Shigella mAb was produced using IpaC and an immunochromatographic strip was developed to detect different serotypes of Shigella in food.

Gold-based immunochromatographic strip for rapid ketoconazole detection

We developed a highly sensitive and specific monoclonal antibody (mAb) for ketoconazole (KCZ) detection in chicken samples. From indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) analysis, the 50% inhibitory concentration of the mAb was 0.7 ng/mL, and the cross-reactivity with fluconazole, imidazole, itraconazole, and voriconazole was <1%. Using indirect competitive enzyme-linked immunosorbent assay, spiked sample recovery was 92.5%–102.7%. Under optimal conditions, we also developed a colloidal gold immunochromatographic assay (CGIA) to detect KCZ residues in chicken samples, with a visual limit of detection of 0.5 ng/g and a cut-off value of 20 ng/g. When data were assessed using liquid chromatography with tandem mass spectrometry, no significant differences were found between assays. Also, strip results were revealed in 10 min. Therefore, our CGIA has great potential for rapidly detecting KCZ residues in chicken samples.

Antibody orientational labeling via staphylococcus A protein to improve the sensitivity of gold immunochromatography assays

The Cry1Ab toxin is usually expressed in genetically modified crops in order to control chewing pests. Although the gold immunochromatography assay (GICA) based on the double-antibody sandwich method has been developed to detect this toxin, its detection sensitivity needs improvement. In this study, Cry1Ab-51 antibodies were immobilized orientationally in a simple and effective way on colloidal gold nanoparticles (CGNPs) using the affinity of staphylococcal protein A (SPA) towards the fragment crystallizable (FC) fragment of mouse immunoglobulin G (IgG). Lateral flow detection test strips, assembled with probes labeled with orientational methods under optimal operational conditions (new probe), were 10 times more sensitive than test strips assembled with probes labeled by adsorption (conventional probe). Experiments showed that the affinity of the new probe was much higher than the conventional probe. The immunochromatography gold strip (ICG strip) assembled using the new probe was highly specific to Cry1Ab with no cross-reaction with other transgenic proteins, and it was proved that the specificity of the new probe had no change. Furthermore, the ICG strips assembled with the new probe could be stored for 12 months under dry conditions without a significant loss of sensitivity. The orientational labeling of the antibodies with SPA on colloidal gold proved to be suitable for improving the sensitivity of the ICG strips.

A colloidal gold-based immunochromatographic strip for rapid detection of SARS-CoV-2 antibodies after vaccination

Vaccination interventions is consideredan important preventive measure to block the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and protect the organism from pathogen infection effectively. However, a quick and accurate technique to evaluate the immune efficacy of the SARS-CoV-2 inactivated vaccine remains scarce. In this paper, an IgM-IgG antibody combined detection colloidal gold immunochromatography assay kit was optimized and developed, which can assess the efficacy of the inactivated SARS-CoV-2 vaccine. We collected fingertip blood samples from 3 vaccinees and 1 unvaccinated sample. The results showed that the proportion of antibody was high after the second shots immunization. The colloidal gold-based immunochromatographic strip is rapid, convenient and easy to operate. It can be used as an auxiliary method for preliminary evaluation of the antibody effect of vaccine recipients, and provide a reference index for the potential clinical application value of the vaccine.

Colloidal gold immunochromatographic assay (GICA) is an effective screening method for identifying detectable anti-SARS-CoV-2 neutralizing antibodies

IntroductionA large number of COVID-19 patients are in recovery, and millions of people are vaccinated for COVID-19 globally. This calls for a rapid screening strategy of SARS-CoV-2 protective antibodies, generated in rehabilitated and vaccinated populations. MethodsSerum samples collected over a follow-up period of six months from 306 COVID-19 cases discharged from Wuhan Tongji Hospital were analyzed. Anti-S Abs were detected by colloidal gold immunochromatographic assay (GICA), and neutralizing antibodies (nAbs) were detected by chemiluminescent microparticle immunoassay (CMIA). ResultsMost COVID-19 survivors tested positive for anti-S Abs (83.7%) and nAbs (98.0%) 6 months after being discharged from the hospital, and the levels of anti-S Abs in the blood were highly positively correlated with nAbs (r = 0.652, P < 0.0001). The positivity rate of nAbs for patients with anti-S Abs positive was 100%. ConclusionsThere is a good agreement between anti-S Abs detected by GICA and nAbs detected by CMIA. It indicates that anti-S Abs detected by GICA may be used as a cheaper screening strategy for detectable SARS-CoV-2 nAbs in COVID-19 convalescent individuals.

Effects of 105 traditional Chinese medicines on the detection of β-agonists in medicine extracts and swine urine based on colloidal gold immunochromatographic assay

Colloidal gold immunochromatographic assay (CGIA) is commonly used for the on-site detection of β-agonists that are sometimes used illegally as feed additives in swine diets. However, few studies have evaluated the causes of false-positive results that sometimes occur when applying CGIA in agricultural settings. In this study, we investigated if this false-positive phenomenon is related to the addition of certain traditional Chinese medicines (TCMs) to swine feed. We established and verified an extraction method for TCMs, and then applied CGIA to detect β-agonists in the extracts of 105 TCMs and in the urine of swine dosed with TCMs, respectively. Liquid chromatography-tandem mass spectrometry was used to validate the results of the urine samples tested positive for β-agonists using CGIA. The results were also verified using TCMs and colloidal gold test strips produced by different manufacturers. The extracts of Citri Reticulatae Pericarpium Viride, Citri Reticulatae Pericarpium, Magnoliae Officinalis Cortex, Chaenomelis Fructus, and Rhodiolae Crenulatae Radix Et Rhizoma were tested positive for β-agonists. Meanwhile, the addition of Citri Reticulatae Pericarpium Viride and Citri Reticulatae Pericarpium to swine feed resulted in false-positive results for β-agonists in swine urine. The results provide a new way to explain false-positive CGIA results and provide valuable information for livestock feeding programs.

Gold nanoparticle-based immunochromatographic assay for detection Pseudomonas aeruginosa in water and food samples

Pseudomonas aeruginosa (P. aeruginosa) is the common infection-causing bacterial pathogen. Conventional methods for the detection of P. aeruginosa are time-consuming, and therefore, a more rapid analytical method is required. Here, monoclonal antibodies (Mabs) against P. aeruginosa (CICC 10419) were prepared and based on paired Mabs, an immunochromatographic assay (ICA) was developed. The ICA strip showed a limit of detection of 2.41 × 104 CFU/mL and the linear range of detection was 3.13 × 104-1.0 × 106 CFU/mL. No cross-reactivity was observed when other common Gram-negative and Gram-positive bacteria were used. The analytical performance of the ICA strip indicated that the developed ICA had good specificity and stability. Moreover, the feasibility of the ICA strip was verified by detecting P. aeruginosa (CICC 10419) in spiked water and food samples. The ICA strip could detect samples contaminated with a low-level of P. aeruginosa (CICC 10419) after 8 h enrichment.

Broad-range and effective detection of human noroviruses by colloidal gold immunochromatographic assay based on the shell domain of the major capsid protein

BackgroundHuman noroviruses (HuNoVs) are a major cause of nonbacterial gastroenteritis in all age groups worldwide. HuNoVs can be detected in vitro using molecular assays such as RT-PCR and RT-qPCR. However, these molecular-based techniques require special equipment, unique reagents, experienced personnel, and extended time to obtain results. Besides, the diversity of viral genotypes is high. Therefore, methods that are rapid, broad-range and effective in the detection of HuNoVs are desiderated for screening the feces or vomit of infected people during outbreaks.ResultsIn this study, a colloidal-gold-based immunochromatographic assay (ICA) was developed for effective detection of HuNoVs in clinical samples. Monoclonal antibodies (MAbs) against the shell (S) domain in the major capsid protein of HuNoVs were used in the ICA. The limitations of detection for HuNoVs in clinical samples were 1.2 × 106 genomic copies per gram of stool sample (gc/g) and 4.4 × 105 gc/g for genogroup I and II (GI and GII) HuNoVs, respectively. A total of 122 clinical samples were tested for HuNoVs by ICA and compared against RT-qPCR. The relative sensitivity, specificity and agreement of ICA was 84.2% (95% CI: 83.6–84.8%), 100.0% (95% CI: 98.5–100.0%) and 87.7% (95% CI: 85.6–89.8%), respectively. No cross-reaction with other common enteric viruses or bacteria was observed. The ICA detected a broad range of genotypes, including GI.1, GI.3, GI.4, GI.6, GI.14, GII.2, GII.3, GII.4, GII.6, GII.13, and GII.17 HuNoVs.ConclusionsThis study demonstrates that ICA targeting the S domain of VP1 is a promising candidate for effectively identifying the different genotypes of HuNoVs in clinical samples with high sensitivity and specificity.

EDTA-K2 Improves the Detection Sensitivity of SARS-CoV-2 IgM and IgG Antibodies by Chelating Colloidal Gold in the Immunochromatographic Assay.

ObjectiveThe coronavirus disease (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is now rapidly spreading globally. Serological tests are an important method to assist in the diagnosis of COVID-19, used for epidemiological investigations. In this study, we aimed to investigate the impact of different types of vacuum collection tubes on the detection of SARS-CoV-2 IgM and IgG antibodies, using the colloidal gold immunochromatographic assay (GICA).Patients and MethodsA total of 112 patients with COVID-19 and 200 healthy control subjects with no infection were enrolled in this study. Their serum and plasma were collected into four different types of vacuum blood collection tubes. SARS-CoV-2 IgM and IgG specific antibodies in the plasma and serum were then detected by GICA and chemiluminescence assay (CA), respectively. In addition, the particle sizes of different colloidal gold solutions in the presence of different anticoagulants and coagulants were evaluated by both laser diffraction (Malvern) and confocal laser microscope, respectively.ResultsOur results revealed that anticoagulated plasma with EDTA-K2 improved the positive detection rate of SARS-CoV-2 IgM antibodies. Furthermore, our results shown that the detection results by GICA and CA were highly consistent, especially, the results of EDTA-K2 anticoagulated plasma detected by GICA was more consistent with CA results. We confirmed that EDTA-K2 could improve the detection sensitivity of SARS-CoV-2 IgG antibodies by chelating excessive colloidal gold compared with sodium citrate or lithium heparin, these methodologies did not appear to cause false positives. Colloidal gold particles could be chelated and aggregated by EDTA-K2, but not by sodium citrate, lithium heparin and coagulants.ConclusionGICA is widely used to detect antibodies for the advantages of convenient, fast, low cost, suitable for screening large sample and require minimal equipment. In this study, we found that EDTA-K2 amplified the positive antibody signal by chelating colloidal gold and improved the detection sensitivity of SARS-CoV-2 IgM and IgG antibodies when using the GICA. Therefore, we suggested that EDTA-K2 anticoagulated plasma was more suitable for the detection of SARS-CoV-2 antibodies.

Changes of antibodies in COVID‑19 patients: A 10‑month prospective study

Objective: To explore the law of antibody changes in patients diagnosed with COVID‑19 after the onset of the disease. Methods: A total of 215 patients who were diagnosed with COVID‑19 by RT‑PCR in Wuchang District, Wuhan City, Hubei Province were recruited as the research subjects. The rapid colloidal gold immunochromatography assay was performed on every newly diagnosed patient at the time points of (10±3) d, (100±3) d, (190±3) d, and (280±3) d after the onset of the disease. Results: In terms of antibody types, among the 215 patients,the positive rate of IgM antibodies was 36.7% at (10±3) d. The antibody levels were 22.5%, 5.0%, and 4.7% at (100±3) d, (190±3) d, and (280±3) d respectively. In general, the levels of IgG antibody were high. The positive rate of antibody within (10±3) days was 87.0%, and the rate decreased to 80.8% at (100±3) d, 49.7% and 46.5% at (190±3) d and (280±3) d, respectively. The number of IgM and IgG antibodies homo‑positive samples gradually decreased over time. At the meantime, the proportion of IgM+IgG antibodies both negative samples gradually increases. According to the clinical classification, in the early stage of the disease, the positive rate of IgM antibody was different in patients with different severity of clinical symptoms. The more severe the clinical symptoms, the higher the positive rate of IgM antibodies. Around 190 days after the onset of symptoms, the positive rate of IgG antibodies decreased more slowly in mild and common patients. At the 280‑day during follow‑up, IgM antibodies showed a higher positive rate in severe and critical patients. From the trend of antibody changes in the same patient within 10 months, among the 70 patients, only 55 cases (32.4%) showed continuous positive in IgG antibody, with 77 cases (45.3%) in the IgG antibody positive‑to‑negative group,and 21 cases (12.4%) in the IgG antibody positive‑to‑negative‑to‑positive group. Three cases (1.8%) showed IgG antibody negative converting to positive. However, there were 14 cases (8.2%) remaining with negative IgG antibody. For IgM antibodies, 97 cases (57.1%) were persistently negative, wth 5 cases (2.9%) in the negative‑to‑positive group, and 65 cases (38.2%) in the positive‑to‑negative group. IgM antibody continued to be positive within 10 months has not been observed yet, and there were 3 cases (1.8%) in the IgM antibody positive‑to‑negative‑to‑positive group. Conclusion: After the new coronavirus infection, the serological response is unstable. In the early stage of the disease, antibody detection has important auxiliary value for the diagnosis of the disease;but in the late stage, the diagnostic value is not great. The antibody response may be positively correlated with the severity of the disease. Nearly 50% of patients can remain positive for IgG antibodies within 10 months, which indicates that nearly half of patients recovering from COVID‑19 can obtain longer‑lasting immunity. However, IgG antibodies in some patients continue or eventually become negative. Whether such patients can get immunity remains to be observed and studied. © 2021, Editorial Board of Medical Journal of Wuhan University. All right reserved.

Sensitive CG-ICA based on heterologous coating antigen and mAb prepared with carbons-linker immunogen

ABSTRACTAmantadine (AMD) is harmful to human health and has been forbidden as an antiviral drug in the livestock and poultry breeding. Thus, a rapid and sensitive detection method for AMD should be established. In this research, we have designed three kinds of haptens and then prepared three kinds of immunogens and coating antigens. A highly sensitive colloidal gold immunochromatographic assay (CG-ICA) for AMD detection by using heterologous coating antigen and mAb prepared with immunogen adding five carbons linker has been established. Under optimal conditions, the cut-off value of the CG-ICA was 2.5 ng/mL by naked eyes. The CG-ICA presented a good signal response to AMD in the concentration range of 0.1–2.5 ng/mL with low LOD at 0.077 ng/mL. These results indicated that the immunogen with carbon linker may obtain high-affinity antibody while the heterologous coating antigen may improve the sensitivity of ICA.