Dual-Labeled Time-Resolved Immunofluorometric Assay for the Simultaneous Quantitative Detection of Hepatitis B Virus Antigens in Human Serum

A New Method for Detection African Swine Fever Virus: Time-resolved Fluorescence Immunoassay

African swine fever (ASF) has severely influenced the swine industry of the whole world. Fast and accurate African swine fever virus (ASFV) antigen detection is very important for ASF prevention. This study aims to establish a new detection method for detection ASFV antigen using time-resolved fluorescence immunoassay (TRFIA) in the nose and mouth discharge. A double antibody sandwich TRFIA method was optimized and established. Recombinant P30 recombinant antigen was captured by its antibodies immobilized on 96-well plate, and then banded together with another detection antibodies labeled with Europium(III) (Eu³⁺) chelates, finally time-resolved analyzer measured the fluorescence intensity. The performance of this TRFIA (sensitivity, specificity and accuracy) was evaluated using the clinical samples and compared with the nucleic acid testing method. The sensitivity of this TRFIA was 0.015 ng/mL (dynamic range 0.24-500 ng/mL) with high specificity. The recovery ranged from 92.00 to 103.62 %, the inter-assay CVs ranged from 5.50 to 11.96 %, and the intra-assay CVs was between 5.20 and 10.53 %. Additionally, the cutoff value was 0.016. TRFIA took only 45 min to generate results, and its detection capability comparable to the nucleic acid detection. This study developed a TRFIA method that could be used for qualitative/quantitative detection of ASFV antigen in pigs nasal discharge, which has high sensitivity, specificity and accuracy. This TRFIA provides a new method for rapidly screening ASFV infection in pigs industry.

Eu3+ /Sm3+ dual-label time-resolved fluoroimmunoassay for measurement of hepatitis C virus antibodies

AIM

To develop a new immunoassay based on the time-resolved fluorescence immunoassay (TRFIA) system for the simultaneous measurement of IgM and IgG antibodies to HCV.

METHODS

Coated recombinant HCV antigens and Eu³⁺ -labeled IgM and Sm³⁺ -labeled IgG antibodies were prepared. HCV-IgM/IgG TRFIA was established and optimized, followed by a methodological assessment. Data were expressed as x ¯ +SD and analyzed using the SPSS 13.0 software. The percentile method was used to calculate cutoff values.

RESULTS

The detection sensitivities of HCV-IgM and HCV-IgG were 0.06 S/CO and 0.15 S/CO, respectively. There was a good linear response from 1:40 to 1:40 960 for HCV-IgM and 1:20 to 1:40 960 for HCV-IgG, when samples strongly positive for HCV-IgM and HCV-IgG were serially diluted from 1:10 to 1:81 920. The average intra-assay coefficients of variation (CV) for HCV-IgM and -IgG were 3.45% and 3.71% and the inter-assay coefficients of variation (CV) were 6.49% and 6.79%, respectively. When HCV-negative/positive sera were tested by ELISA and using established kits, the negative, positive, and total conformity rates for HCV-IgM were 93.3% (28/30), 100% (25/25), and 96.4% (53/55), and those for HCV-IgG were 93.3% (28/30), 100% (35/35), and 96.9% (63/65), respectively. Additionally, the established kit exhibited good stability, with declines in fluorescence values to 11.1% and 9.5%, respectively, after storage at 37°C for 7 days.

CONCLUSION

We established a dual-label HCV-IgM/IgG TRFIA assay with a wide detection range, high specificity, high sensitivity, good stability, and good clinical value for the simultaneous measurement of HCV-IgM and HCV-IgG titers in a single test.

Fluorescence ELISA based on glucose oxidase-mediated fluorescence quenching of quantum dots for highly sensitive detection of Hepatitis B

Herein, we present a novel sandwich fluorescence enzyme linked immunosorbent assay (ELISA) for highly sensitive detection of Hepatitis B virus surface antigen (HBsAg) based on glucose oxidase (GOx)-induced fluorescence quenching of mercaptopropionic acid-modified CdTe quantum dots (MPA-QDs). In this system, hydrogen peroxide (H₂O₂) sensitive MPA-QDs was used as a signal output, and glucose oxidase (GOx) was used as label which can generate H₂O₂ via catalytic oxidation of glucose. The proposed method showed dynamic linear detection of HBsAg both in the range of 47pgmL^-1 ~ 380pgmL^-1 and 0.75ngmL^-1 ~ 12.12ngmL^-1. The detection limit of the proposed fluorescence ELISA was 1.16pgmL^-1, which was approximately 430-fold lower than that of horseradish peroxidase (HRP)-based conventional ELISA. The average recoveries for HBsAg-spiked serum samples ranged from 98.0% to 126.8% with the relative standard derivation below 10%, thus indicating acceptable precision and high reproducibility of the proposed fluorescence ELISA for HBsAg detection. Additionally, the developed method showed no false positive results analyzing 35 real HBsAg-negative serum samples, and exhibited excellent agreement (R²=0.9907) with a commercial time-resolved fluorescence immunoassay (TRFIA) kit for detecting 31 HBsAg-positive serum samples. In summary, the proposed method based on fluorescence quenching of H₂O₂ sensitive QDs is considerably to be an excellent biodetection platform with ultrahigh sensitivity, good accuracy and excellent reliability.