A Simple Colorimetric Analytical Assay for the Determination of Tetracyclines Based on In-situ Generation of Gold Nanoparticles Coupling with a Gold Staining Technique.

The development of simple and sensitive detection methods for tetracyclines (TCs) is crucial for their routine detection. The present study developed a colorimetric method for the detection of TCs based on the in-situ generation of AuNPs, which were subsequently coupled with a gold staining reaction. Briefly, TCs containing phenolic groups reduce HAuCl4 to form gold nanoparticles (AuNPs) as gold seeds. In the gold staining process, the gold seeds catalyze the reduction of HAuCl4 by NH2OH to form gold atoms that deposit on the surface of AuNPs, resulting in the enlargement of AuNPs. Sensitive detection of TCs was achieved by employing the gold staining technique. As low as 14, 18.9, and 1.98 nM of oxytetracycline (OTC), tetracycline (TC), and doxycycline (DC), respectively, could be sensitively detected. The proposed method also exhibited good repeatability and specificity, and then was applied to the determination of OTC in milk samples.