Rapid Detection of Tulathromycin in Milk with Quantum Dot-Based Fluorescence-Linked Immunosorbent Assay

Tulathromycin (TULA) is primarily used for treating respiratory diseases in livestock. However, its misuse may lead to bacterial resistance and poses potential health risks such as chronic toxicity and allergic reactions through the food chain. Therefore, it is essential to develop rapid and accurate detection methods. In this study, two quantum dot-based fluorescent immunosorbent assays-direct competitive FLISA (dc-FLISA) and indirect competitive FLISA (ic-FLISA)-were established for detecting TULA residues in milk. The dc-FLISA exhibited a half-maximal inhibitory concentration (IC₅₀) of 1.99 ng·mL^-1, a limit of detection (LOD) of 0.018 ng·mL^-1, and a detection range of 0.058-69.18 ng·mL^-1. The ic-FLISA showed an IC₅₀ of 0.89 ng·mL^-1, an LOD of 0.005 ng·mL^-1, and a detection range of 0.019-42.65 ng·mL^-1. Spiked recovery tests in milk demonstrated recovery rates ranging from 97.41% to 101.02% for dc-FLISA and from 97.48% to 100.65% for ic-FLISA, with coefficients of variation below 10%. In summary, two simple, effective, rapid, and sensitive methods were successfully developed for detecting TULA residues in milk.