Detection of Bovine Brucellosis Antibodies in Serum and Milk Using Quantum Dot Microspheres Immunochromatographic Assay.

Brucellosis, a zoonotic disease caused by Brucella, requires rapid, accurate, and sensitive diagnostic methods for effective prevention and control. This study presents the development of a fluorescence microsphere immunochromatographic assay (QDMs-ICA) for detecting anti-Brucella antibodies in bovine serum and milk. Lipopolysaccharide (LPS) from the Brucella abortus strain A19 was immobilized on the nitrocellulose membrane (NC membrane) as the test line (T-line), while rabbit anti-SPG polyclonal antibody was applied as the control line (C-line). Recombinant streptococcal protein G conjugated with quantum dot microspheres (QDMs-SPG) served as the detection conjugate. After optimizing the preparation parameters of QDMs-ICA, the method demonstrated sensitivities of approximately 0.98 IU/mL for bovine serum and 1.56 IU/mL for milk. No cross-reactions were observed with antibody-positive sera from Coxiella burnetii, Mycobacterium avium paratuberculosis, Mycobacterium tuberculosis, Chlamydia abortus, Bacillus anthracis, Escherichia coli O157:H7, Vibrio cholerae or Salmonella, indicating excellent specificity. In intra- and inter-batch repeatability tests, the coefficient of variation (CV) remained below 15%, confirming good reproducibility. The detection limit remained stable after storage at 37 °C for 7 days. Parallel testing of 150 bovine serum samples and 80 milk samples showed a high degree of concordance with the ID-VET commercial kit, with coincidence rates of 97.3% and 96.3%, respectively. These results demonstrate that QDMs-ICA offers high specificity, sensitivity, repeatability, and reliability, making it an effective tool for the rapid detection and epidemiological monitoring of brucellosis.