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

## TL;DR

This paper introduces two new methods using quantum dots to quickly and accurately detect tulathromycin in milk.

## Contribution

The development of two quantum dot-based fluorescence-linked immunosorbent assays for rapid detection of tulathromycin in milk.

## Key findings

- The dc-FLISA had an IC50 of 1.99 ng·mL−1 and LOD of 0.018 ng·mL−1.
- The ic-FLISA showed better sensitivity with an IC50 of 0.89 ng·mL−1 and LOD of 0.005 ng·mL−1.
- Both methods achieved high recovery rates (97-101%) with low variability in milk samples.

## Abstract

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.