Colorimetric Sensing of Tetracyclines in Milk Based on the Assembly of Cationic Conjugated Polymer-Aggregated Gold Nanoparticles

We have developed an unlabeled sensing strategy for tetracycline (TET) detection in aqueous solutions and milk by using an aptamer–gold nanoparticle (AuNP)-based colorimetric method. Aptamers were found to be absorbed on the Au surface which stabilizes the AuNPs against conditions of high poly(diallyldimethylammonium) strength. The introduction of TET had reduced aptamers to form a TET–aptamer complex, so that the following cationic polymers could aggregate AuNPs and cause a remarkable change in color. Through this phenomenon, TET can be detected qualitatively and quantitatively by means of absorbance. This unlabeled strategy saves both the time and cost for detection, which could selectively detect TET at concentrations as low as 1 μM and 45.8 nM for the naked eyes and colorimetric detector, respectively. In addition, this biosensor exhibited high selectivity over other antibiotics with an excellent recovery in the detection of milk. Because of the advantages of this sensor, we hope this will be the basis for an assay for the sensitive, colorimetric detection of a wide range of molecular analytes.