Colloidal Gold-based Immunochromatographic Assay Research Articles

Colorimetric and Reverse Fluorescence Dual-Signal Readout Immunochromatographic Assay for the Sensitive Determination of Sibutramine.

Later flow immunochromatographic assay has been widely used in clinical, environmental, and other diagnostic applications owing to its high sensitivity and throughput. However, most immunoassays operate in the "turn-off" mode for detecting targets of low molecular weight. The signal intensity decreases as the analyte concentration increases, which poses a challenge for achieving ultrasensitive detection at low concentrations and is counterintuitive to new users. In this work, a fluorometric immunochromatographic assay (FICA) is developed to simultaneously read "turn-on" fluorescent and "turn-off" colorimetric signals, where ZnCdSe/ZnS quantum dots act as fluorescence donors and gold nanoparticles (AuNPs) act as quenchers. The fluorescent signal (excitation/emission wavelengths of 365/525 nm) is positively correlated with analytes' concentration. Taking sibutramine (SBT) as the analysis target, the visual limit of detection for SBT reached 3.9 ng/mL, and the limit of Quantitation was 5.0 ng/mg in spiked samples. The developed FICA achieves a high sensitivity in SBT detection, which is much lower than that of the colloidal gold-based immunochromatographic assay. This dual-function detection mode has great potential to be used as a rapid on-site semiquantitative method, providing an alternative mode for the determination of low levels of target analytes.

Ultrasensitive detection of imatinib in human serum using a gold-based paper sensor

Imatinib is the tyrosine kinase inhibitor of choice for the treatment of chronic myeloid leukemia and gastrointestinal stromal tumors. However, imatinib has drawbacks such as drug resistance and significant differences in pharmacokinetics within patients. Therefore, a colloidal gold-based immunochromatographic assay (CG-IA) was developed for measuring and monitoring imatinib in human serum. An imatinib derivative containing carboxyl groups was used for the synthesis of the immunogen, and 4-(4-methyl-1-piperazinylmethyl) benzoic acid was selected as the hapten for the heterologous coating antigen. Next, a highly sensitive and specific monoclonal antibody (mAb), 2F7 was screened for the construction of a CG-IA, with an IC50 value of 0.091 ng/mL. For the qualification of imatinib in human serum, the visual limit of detection (vLOD) and cut-off values of the CG-IA were 2 and 20 ng/mL, respectively. For quantitative detection, the calculated LOD value of the CG-IA was 0.068 ng/mL, with a linearity range of 1.004 and 23.087 ng/mL. The recovery rate of spiked serum samples was between 88.24 % and 104.75 %. In addition, the concentration of imatinib in the serum samples from 10 patients was detected by CG-IA and revealed a good correlation with those from LC-MS/MS. These results indicated that the developed gold-based paper sensor could become an effective tool for the rapid monitoring of imatinib in human serum samples.

The diagnostic value of GICA used for intraoperative lymph node FNA-Tg measurement to evaluate thyroid cancer metastases.

It is crucial to diagnose lymph node (LN) metastases (LNM) before or during thyroid carcinoma surgery. Measurement of thyroglobulin (Tg) in the fine needle aspirate washout (FNA-Tg) is useful to assist in the diagnosis of LNM for papillary thyroid carcinoma (PTC). This study aimed to assess the diagnostic performance of a new technique based on a colloidal gold-based immunochromatographic assay (GICA) for intraoperative FNA-Tg in diagnosing LNM. This study is registered with chictr.org.cn, ID: ChiCTR2200063561 (registered 11 September, 2022). This prospective study enrolled 51 PTC patients who underwent cervical LN dissection. A total of 150 LNs dissected from the central and lateral compartments were evaluated by FNA-Tg-GICA at three different time points and compared with frozen sections and the conventional Tg measurement method electrochemiluminescence immunoassay (ECLIA). Receiver operating characteristic curve (ROC) and area under the curve (AUC), cutoff value to discriminate benign and malignant LNs, sensitivity, specificity, and accuracy were provided. The cutoff value of FNA-Tg to predict LNM was 110.83 ng/mL for ECLIA and 13.19 ng/mL, 38.69 ng/mL, and 77.17 ng/mL for GICA at 3, 10, and 15 min, respectively. There was no significant difference between the AUCs of GICA at different time points compared to using ECLIA and frozen sections. Besides, the diagnostic performance of GICA and ECLIA showed no significant difference in evaluating LNM from central and lateral compartments or between the TgAb-positive subgroup and TgAb-negative subgroup. GICA is a promising method for intraoperative FNA-Tg measurement and has high value in predicting LNM. It may be a novel alternative or supplementary method to frozen section or ECLIA.

Development of a colloidal gold-based immunochromatographic assay for rapid detection of nasal mucosal secretory IgA against SARS-CoV-2.

Infection with SARS-CoV-2 begins in the upper respiratory tract and can trigger the production of mucosal spike-specific secretory IgA (sIgA), which provides protection against reinfection. It has been recognized that individuals with high level of nasal spike-specific IgA have a lower risk of reinfection. However, mucosal spike-specific sIgA wanes over time, and different individuals may have various level of spike-specific sIgA and descending kinetics, leading to individual differences in susceptibility to reinfection. A method for detecting spike-specific sIgA in the nasal passage would be valuable for predicting the risk of reinfection so that people at risk can have better preparedness. In this study, we describe the development of a colloidal gold-based immunochromatographic (ICT) strip for detecting SARS-CoV-2 Omicron spike-specific sIgA in nasal mucosal lining fluids (NMLFs). The ICT strip was designed to detect 0.125 μg or more spike-specific sIgA in 80 μL of NMLFs collected using a nasal swab. Purified nasal sIgA samples from individuals who recently recovered from an Omicron BA.5 infection were used to demonstrate that this ICT strip can specifically detect spike-specific sIgA. The signal levels positively correlated with neutralizing activities against XBB. Subsequent analysis revealed that people with low or undetectable levels of spike-specific sIgA in the nasal passage were more susceptible to SARS-CoV-2 reinfection. This nasal spike-specific sIgA ICT strip provides a non-invasive, rapid, and convenient method to assess the risk of reinfection for achieving precision preparedness.

Development of ic-ELISA and colloidal cold-based immunochromatographic assay for red 2G detection in fruit drinks, red wine, and yoghurts

Red 2G (R2G), a cheap industrial colorant, cannot be added to food. An anti-R2G monoclonal antibody (mAb) was prepared by immunizing mice with the conjugate of R2G hapten and protein, which based on the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) method. Indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) and colloidal gold-based immunochromatographic assay (CG-ICA) methods were used to determine R2G in fruit drinks, red wine, and yoghurts. A standard curve of the developed ic-ELISA showed that the IC50 of the anti-R2G mAb was 1.02 ng/mL, and limit of detection value (LOD) was 0.21 ng/mL. For the CG-ICA developed, the visual limit of detection values (vLOD) were 2 ng/mL and cut-off values of 100 ng/mL in samples. The results indicated that these two methods could be used to quickly detect R2G in fruit drinks, red wine, and yoghurts.

Development of enzyme-linked immunosorbent assay and colloidal gold-based immunochromatographic assay for the rapid detection of gentamicin in chicken muscle and milk

• A specific monoclonal antibody against gentamycin was obtained. • Based on mAb, one-step ic-ELISA and GICA methods were developed. • Two immunoassays can be applied for the detection of gentamycin in real samples. A specific anti-gentamicin (GEN) monoclonal antibody (mAb) was used to develop an indirect competitive ELISA (ic-ELISA) and a colloidal gold immunochromatographic assay (GICA) for the determination of GEN residues in chicken muscle and milk. The result of ic-ELISA showed that the limits of detection (LOD) for GEN in chicken muscle and milk samples ranged from 0.54 µg kg −1 –0.57 µg kg −1 . As for the GICA method, the LOD of GEN in chicken muscle and milk were 10 µg kg −1 and 10 µg kg −1 , respectively. The GEN recovery of the two methods ranged from 83.8%–112.2%. In the actual samples detection, the ELISA and GICA methods had a good correlation with high-performance liquid chromatography (HPLC) results. These indicated that the methods established in this study could be a candidate tool for the rapid large-scale screening of GEN in animal-derived foods.

Development of Immunochromatographic Assay for the Rapid Detection of Mycoplasma capricolum subsp. capripneumoniae Antibodies.

Mycoplasma capricolum subsp. capripneumoniae (Mccp) is the cause of contagious caprine pleuropneumonia (CCPP), which is a highly significant respiratory disease in goats leading to significant economic losses in Africa and Asia. Currently available procedures for the diagnosis of CCPP have some limitations in sensitivity, specificity, operation time, requirement of sophisticated equipment or skilled personnel, and cost. In this study, we developed a rapid, sensitive, and specific colloidal gold-based immunochromatographic assay (GICA) strip for the efficient on-site detection of antibodies against Mccp in the serum within 10 min. For the preparation of this colloidal GICA strip, recombinant P20 protein, the membrane protein of Mccp, was expressed by Escherichia coli prokaryotic expression system after purification was used as the binding antigen in the test. The rabbit anti-goat immunoglobulin G labeled with the colloidal gold was used as the detection probe, whereas the goat anti-rabbit immunoglobulin G was coated on the nitrocellulose membrane as the control line. The concentration of the coating antibody was optimized, and the effectiveness of this colloidal GICA strip was evaluated. Our results proved that the detection limit of the test strip was up to 1:64 dilutions for the Mccp antibody-positive serum samples with no cross-reactivity with other pathogens commonly infecting small ruminants,including goat pox virus, peste des petits ruminants virus, foot-and-mouth disease virus type A, or other mycoplasmas. Moreover, the colloidal GICA strip was more sensitive and specific than the indirect hemagglutination assay for the detection of Mccp antibodies. The 106 clinical serum samples were detected by the colloidal GICA strip compared with the complement fixation test, demonstrating an 87.74% concordance with the complement fixation test. This novel colloidal GICA strip would be an effective tool for the cost-effective and rapid diagnosis of CCPP in the field.

Ultrasensitive Detection of Phenolphthalein in Slimming Products by Gold-Based Immunochromatographic Paper

An anti-phenolphthalein monoclonal antibody (mAb) was prepared based on the N' N-carbonyldiimidazole (CDI) method through phenolphthalein conjugated with proteins. Indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) and colloidal gold-based immunochromatographic assay (ICA) methods were used to determine phenolphthalein in slimming products. A standard curve was established, and the IC50 and limit of detection of ic-ELISA were 0.95 and 0.10 ng/mL with a linear detection range of 0.27-3.37 ng/mL. The developed ICA was used to detect phenolphthalein in tablets, capsules, and slimming tea samples with visual limit of detection values of 10 ng/mL, and cut-off values of 200 ng/mL. The results indicated that these two methods could be used to quickly detect phenolphthalein in slimming products.

Health Issues and Immunological Assessment Related to Wuhan's COVID-19 Survivors: A Multicenter Follow-Up Study.

Background: Currently, a large number of hospitalized coronavirus infectious disease-2019 (COVID-19) patients have met the clinical discharge criteria and have been discharged. Little is known about the sequelae and herd immunity, two important factors influencing the life quality and safety of COVID-19 survivors.Methods: Discharged COVID-19 patients from four medical facilities in Wuhan, China, were followed in order to record and investigate possible post-COVID-19 sequelae and herd immunity. After hospital discharge, patients reported to Fangcang shelter hospitals for an initial 14-day period of mandatory clinical monitoring. After release from these shelter hospitals, patients returned home for self-quarantine. Real-time quantitative PCR (RT-qPCR) was used for severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) detection. Colloidal gold-based immunochromatographic strip assay (ICGSA) was used for anti-SARS-CoV-2 immunoglobulin G (IgG) and immunoglobulin M (IgM) antibody testing. The data for this study are derived from case reports, medical records, and self-reports.Results: A total of 3,677 COVID-19 survivors [median age = 59 years, interquartile range (IQR) = 47–68, range = 10–98; 55.5% female] who were released from four hospitals in Wuhan, China, between January 18 and March 29, 2020 were followed for a median of 144 days (IQR = 135–157). During follow-up, 976 (26.5%) patients had at least one post-COVID-19 sequela. The incidence of post-COVID-19 sequelae among elderly COVID-19 survivors (age ≥60 years) was slightly increased compared to that of young COVID-19 survivors (age <60 years; relative risk = 1.05, 95% CI = 1.02–1.10, p = 0.007). During follow-up, a dramatic reduction of anti-SARS-CoV-2 IgG (88.0%, 95% CI = 84.2–90.4) and IgM (93.2%, 95% CI = 88.5–96.4) antibodies was observed. Among these COVID-19 survivors, 1.2% (n = 45) retested positive for SARS-CoV-2 and 1.0% (n = 37) died during follow-up. Of those who died during follow-up, 70.3% were male and all were negative for both IgG and IgM, except for one person who was IgG-positive.Conclusions: Our study documents significant post-COVID-19 sequelae that impair functions of multiple organ systems in COVID-19 survivors, suggesting that the long-term effects of this disease will negatively impact survivors' quality of life, continue to strain health care systems, and result in extended periods of lost productivity. Furthermore, female gender and anti-SARS-CoV-2 immunity may play an essential role in the survival after COVID-19 infection.

False-positive colloidal gold-based immunochromatographic strip assay reactions for antibodies to SARS-CoV-2 in patients with autoimmune diseases.

The outbreak of the novel 2019 coronavirus disease (COVID-19) was declared a global pandemic by the World Health Organization (WHO) on March 11, 2020. The diagnosis of COVID-19 is frequently based on a positive serological test. We noted the occurrence of false-positive results for COVID-19 in the colloidal gold-based immunochromatographic strip (ICS) assay in sera from patients with autoimmune diseases (ADs). This study aimed to evaluate the possible reasons for the false-positive results in two ICS assays (Wondfo ICS and Innovita ICS) and to investigate the effect of urea dissociation in reducing false-positive results. The sera of 135 patients with ADs, 13 confirmed COVID-19 patients, 95 disease controls, and 120 healthy controls were tested for immunoglobin M (IgM) and IgG against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using Wondfo and Innovita ICS kits. The distributions of auto-antibodies in antibody-positive and antibody-negative groups were also compared, and bivariable logistic regression was used to assess auto-antibodies associated with false-positive results. A urea dissociation test of ICS was performed for the SARS-CoV-2 antibody-positive samples. Specificity of Wondfo ICS for the 95 disease controls was 94.74% compared to 98.95% and 96.84% for Innovita SARS-CoV-2 IgM and IgG, respectively. Specificity of Wondfo ICS for the 120 healthy controls was 97.5% compared to 100% and 99.17% for Innovita SARS-CoV-2 IgM and IgG, respectively. Specificity of Wondfo ICS for AD patients was 73.33% compared to 97.78% and 96.30% for Innovita SARS-CoV-2 IgM and IgG, respectively. Sensitivity was 74.07% for Wondfo compared to 70.37% for Innovita IgM and 66.67% for Innovita IgG. Using the Wondfo ICS, the percentage of elevated rheumatoid factor (RF) level (>20 IU/mL) was higher in the SARS-CoV-2 antibody-positive group compared with the antibody-negative group [27/36 (75.0%) vs. 34/99 (34.34%), P=0.001]. The elevated RF was associated with antibody positivity, with an odds ratio of 4.671 [95% confidence interval (CI), 1.88-11.69]. The specificity of the Wondfo ICS assay for the AD patients was increased from 73.33% to 94.07% after the urea dissociation assay. An elevated serum RF level could lead to false-positive results when detecting SARS-CoV-2 antibodies using the Wondfo ICS kit, and the urea dissociation assay would be helpful in reducing the incidence of false-positive results.

Development of a Colloidal Gold Immunochromatographic Assay for Duck Enteritis Virus Detection Using Monoclonal Antibodies.

Duck viral enteritis is a highly contagious and fatal disease of commercial waterfowl flocks. The disease occurs sporadically or epizootically in mainland China due to insufficient vaccinations. Early and rapid diagnosis is important for preventive intervention and the control of epizootic events in clinical settings. In this study, we generated two monoclonal antibodies (MAbs) that specifically recognized the duck enteritis virus (DEV) envelope glycoprotein B and tegument protein UL47, respectively. Using these MAbs, a colloidal gold-based immunochromatographic assay (ICA) was developed for the efficient detection of DEV antigens within 15 min. Our results showed that the detection limit of the developed ICA strip was 2.52 × 103 TCID50/mL for the virus infected cell culture suspension with no cross-reactivity with other pathogenic viruses commonly encountered in commercially raised waterfowl. Using samples from experimentally infected ducks, we demonstrated that the ICA detected the virus in cloacal swab samples on day three post-infection, demonstrating an 80% concordance with the PCR. For tissue homogenates from ducks succumbing to infection, the detection sensitivity was 100%. The efficient and specific detection by this ICA test provides a valuable, convenient, easy to use and rapid diagnostic tool for DVE under both laboratory and field conditions.

Development and evaluation of multi-epitope protein p72 (MeP72) for the serodiagnosis of African swine fever.

African swine fever (ASF) is an acute and severe infectious disease that seriously endangers the global porcine industry. In order to develop ASF serodiagnostic reagents with high specificity and sensitivity, in the present study, the antigenic epitopes of P72 protein of African swine fever virus (ASFV) were analyzed, and the ASFV multi-epitope fusion gene MeP72 in tandem with the dominant linear epitopes was constructed. The recombinant multi-epitope fusion MeP72 (reMeP72) was prepared in Escherichia coli. A colloidal gold-based immunochromatographic assay (CGIA) based on reMeP72 was developed for the detection of antibodies against ASFV. A total of 139 pig clinical serum samples were used for assessment of the potential diagnostic value of reMeP72. The results showed that CGIA did not cross-react with positive sera of viruses, such as classical swine fever virus (CSFV), porcine circovirus type 2 (PCV2), pseudorabies virus (PRV), porcine reproductive and respiratory syndrome virus (PRRSV) and swine influenza virus (SIV), showing high specificity. Sensitivity analysis showed that CGIA could detect ASFV-positive serum at a dilution of 1:64. Compared with commercial ASFV kits, the sensitivity and specificity of ASFV CGIA based on reMeP72 protein were 85.7% and 97.6%, respectively. The agreement rate of the two methods was 96.4%, showing a good detection performance. The results indicated that the reMeP72 was of potential value for the serodiagnosis of ASF. Keywords: African swine fever virus; P72 gene; antigenic protein; colloidal gold-based immunochromatographic assay.

COVID-19 Antibody Prevalence From July to September 2020: One Army Infantry Brigade's Experience.

Lab companies developed serology tests for antibody detection of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) with United States Food and Drug Administration (FDA) emergency use authorization. Antibody detection uses purified proteins of SARS-CoV-2 to determine antibody binding via enzyme-linked immunosorbent assay, chemiluminescent immunoassay (CLIA), or colloidal gold-based immunochromatographic assay. With the advent of coronavirus disease 2019 (COVID-19), nucleic acid amplification technology (NAAT) SARS-CoV-2 testing for active infection was not widely available to healthy, active-duty Soldiers. The purpose of this surveillance survey was to determine the prevalence of prior SARS-CoV-2 infection and symptoms of COVID-19 within a mechanized infantry brigade. Active-duty military Servicemembers (= 18 years) from a mechanized infantry brigade provided serum samples for testing for the Elecsys® Anti-SARS-CoV-2 qualitative antibody test from June to September 2020 at Joint Base Lewis McChord (JBLM). In addition, participants filled out a questionnaire for symptoms and exposure to COVID-19 from January to September 2020. The surveillance team collected and analyzed antibody testing results and questionnaires from participants for antibody positivity rates and symptom prevalence. A total of 264 participants were tested, with one (0.4%) participant testing positive for the SARS-CoV-2 antibody. On the questionnaire, 144 of 264 (54.5%) endorsed symptoms of COVID-19 from January to September 2020. The most common symptoms were headache (35%), rhinorrhea (34%), cough (35%), and sore throat (31%). A total of 31 respondents (12%) had been quarantined as a trace contact to a COVID-19 positive patient. While there are limitations inherent to SARS-CoV-2 antibody testing and the survey, prevalence of prior SARS-CoV-2 infection is low. In this sample, symptoms for COVID-19 were prevalent with significant days of duty lost. Prevalence of prior SARS-CoV-2 infection in this sample may be generalizable to the larger brigade. Prevalence of symptoms of possible COVID-19 are not generalizable to the larger brigade. There is utility to further studies of SARS-CoV-2 antibody prevalence in military populations for purposes of vaccination triaging and deployment readiness.

Enzyme-linked immunosorbent assay and immunochromatographic strip for rapid detection of atrazine in three medicinal herbal roots

Objectives: An enzyme-linked immunosorbent assay (ELISA) and colloidal gold-based immunochromatographic (ICG) strip assay will be developed for the rapid and high-throughput detection of atrazine (ATZ) in medicinal herbs. Methods: A monoclonal antibody against ATZ was obtained after the immunization of mice, cell fusion, and hybridoma screening, and the antibody was used to develop direct competitive ELISA (dcELISA) and the ICG strip assay. Results: Both dcELISA and ICG strip methods were established, optimized, and validated for the detection of ATZ in Salviae miltiorrhizae radix et rhizome, Astragali radix, and Isatidis radix. dcELISA had a half-maximum inhibition concentration of 10.56 ng/mL (Salviae miltiorrhizae radix et rhizome), 7.6 ng/mL (Astragali radix), and 8.15 ng/mL (Isatidis radix). The limit of detection (LOD) of the ICG strip assay was 12.5 ng/mL (Salviae miltiorrhizae radix et rhizome), 12.5 ng/mL (Astragali radix), and 6.25 ng/mL (Isatidis radix) in different herb matrices. Due to the recognition characteristics of the monoclonal antibody for the pesticides ATZ, propazine, sebuthylazine, and prometryn, the detection results of real samples by the two immunoassays were confirmed by liquid chromatography–tandem mass spectrometry, which proved the accuracy and reliability of the established methods. Conclusion: The proposed dcELISA and ICG strip methods were suitable for the rapid, convenient, and high-throughput detection of ATZ in these medicinal herbs.

Colloidal gold-based immunochromatographic strip assay for the rapid detection of diminazene in milk

ABSTRACT Diminazene (DIM) is widely used to treat trypanosomiasis in livestock, but its residues in animal products can cause food safety problems. Thus, a rapid colloidal gold-based immunochromatographic strip assay was established to analyse DIM residue in milk samples. A highly sensitive and specific monoclonal antibody (mAb) against DIM was produced with a new synthetic immunogen by the active ester method. The titre of the prepared antibody was up to 1:1.0 × 106, the affinity constant was 2.2 × 108 L mol−1 and the half-maximal inhibitory concentration (IC50) was 0.4 ng mL−1 based on enzyme-linked immunosorbent assay (ELISA). Then, the colloidal gold-labelled mAb probe was successfully prepared and used for preparing the immunochromatographic strip. The strip showed high sensitivity and specificity, the IC50 for DIM was 5.2 ng mL−1, the limit of detection was 1.2 ng mL−1 and the linear range of detection was 1.8–15.4 ng mL−1. The average recoveries ranged from 89.5% to 91.7%, and coefficients of variation were 6.6–7.2%. The immunochromatographic strip assay can be employed in the rapid detection of DIM residue in milk samples.

Sensitive immunoassays based on a monoclonal antibody for detection of marbofloxacin in milk

Marbofloxacin (MBF) is a key class of synthetic fluoroquinolone antibiotic that is commonly used as a veterinary drug. However, excess residue of MBF in animal-derived food samples, such as milk, is harmful to consumers. In this study, 4 mAb against MBF, namely, M4E3, M7A6, M3C7, and M5C6, were produced. Indirect competitive (ic) ELISA revealed that the M4E3 exhibited the highest sensitivity with a half-maximal inhibitory concentration (IC50) of 0.07 ng/mL and a limit of detection of 0.01 ng/mL for detection of MBF. The results of the cross-reactivity experiment revealed that the M4E3 could detect lomefloxacin, ofloxacin, fleroxacin, pefloxacin, danofloxacin, and enrofloxacin sensitively with IC50 of 0.02, 0.07, 0.18, 0.27, 0.30, and 0.32 ng/mL, respectively. Meanwhile, a cross-reactivity experiment showed that the M4E3 had a crossover rate of more than 20% with these fluoroquinolone analogs. A weak crossover rate below 1.11% was observed with 14 other fluoroquinolone analogs. The recovery rate of MBF in milk ranged from 72.28% to 129.19%, which showed that the developed indirect competitive ELISA was effective in detecting MBF in milk. Furthermore, a visual colloidal gold-based immunochromatographic assay was developed for detecting MBF with a cut-off value of 1 ng/mL in both phosphate-buffered saline and a milk sample by using this mAb. Given this sensitive mAb, both indirect competitive ELISA and colloidal gold-based immunochromatographic assay could be effective screening tools for detection of MBF in milk.

Assessment of patients who tested positive for COVID-19 after recovery

Assessment of patients who tested positive for COVID-19 after recovery

The Strategic Alliance between Clinical and Molecular Science in the War against SARS-CoV-2, with the Rapid-Diagnostics Test as an Indispensable Weapon for Front Line Doctors.

Our work concerns the actual problem of spread of SARS- CoV-2 outbreak which requires fast and correct as possible answer. In current scenario, the need of rapid answer put away the imperative of proper methodology. We focus on the serogical immunoassay for diagnosis of Covid-19 as an important weapon not only for diagnostic purpose, but also for epidemiologic one. The right equilibrium between high speed, low cost and accuracy is obtained with easy-to-use decentralized point-of-care test as the colloidal gold-based immunochromatographic strip assay which detects IgM and IgG antibodies directed against SARS-CoV-2. As our aim is to evaluate the efficacy of Covid-19 rapid tests and of serological assays in real-life settings, we designed a research protocol aimed to establish how to use correctly these diagnostics, taking into account the different possible clinical and epidemiological scenarios.

Colloidal gold-based immunochromatographic strip assay for the rapid detection of bacitracin zinc in milk

In this study, a murine monoclonal antibody (mAb) of 6D2-G10 against bacitracin zinc (BAC) was produced and applied to an immunochromatographic strip (ICS) for the initial detection of BAC in milk. The ICS with a cut-off value of 25 ng/mL could be perceived by the naked eye within 10 min. With the assist of the strip reader, the limit of detection (LOD) was measured as 0.82 ng/mL, the half-maximal inhibitory concentration (IC50) was recorded as 3.16 ng/mL, and the linear detection range was from 0.97 to 10.30 ng/mL. The recoveries ranged from 87.7% to 96.0% with the highest coefficient of variation (CV) of 9.1% in the intra-assay and from 84.3% to 90.2% with the highest CV of 10.7% in the inter-assay. In short, the established ICS provided a serviceable analytical tool for qualitatively and quantitatively monitoring BAC in milk.

Visual and fluorometric lateral flow immunoassay combined with a dual-functional test mode for rapid determination of tetracycline antibiotics.

A fluorometric immunochromatographic assay (FICA) is described where ZnCdSe/ZnS quantum dots (QDs) act as fluorescent label and gold nanoparticles (AuNPs) act as quencher. The assay works in the "turn-on" mode, i.e. the fluorescent signal (best measured at excitation/emission wavelengths of 302/525nm) increases with the increase of analyte concentration. This assay can detect tetracycline antibiotics including tetracycline, oxytetracycline, chlortetracycline, and doxycycline. It is not interfered by other veterinary drugs. The visual limits of detection (LODs) for the tetracycline antibiotics are 2μg·L-1 in buffer, 20μg·L-1 in milk, and 40μg·kg-1 in animal muscle tissue. The assay (including sample treatment) can be performed within 30min. The FICA based on "turn on" mode is more sensitive than the colloidal gold-based immunochromatographic assay (CGICA) and quantum dot-based immunochromatographic assay (QDICA) based on "turn off" mode using either AuNPs or QDs as signal labels. One strip can simultaneously provide the fluorescent test results in the"turn on" mode on the basis of QD luminescence quenching under UV light. The colorimetric test is of the "turn off" mode based on the formation of a red coloration due to the use of AuNPs under natural light. The use of such a dual-functional test mode allows for rapid semi-quantitative determination of tetracycline antibiotics in milk and tissue samples. Graphical abstract Schematoc of a fluorometric immunochromatographic assay (FICA) based on fluorescence quenching of quantum dot (QD) by gold nanoparticle (AuNP) combined with a dual-functional test mode under UV light (turn on mode) and natural light (turn off mode) to visually detect tetracycline antibiotics.