A target-induced displacement-assisted colorimetric aptasensor for tetracycline detection based on Co MOF@Au NPs nanozymes.

Tetracycline (TC) residues in milk present a potential risk to food safety and human health, highlighting the urgent need to develop rapid and reliable detection strategies. Herein, a target-induced displacement (TID)-based colorimetric aptasensor was assembled for the sensitive detection of TC using oxidase (OXD)-like nanozymes. The flower-like gold nanoparticle-decorated cobalt-based metal-organic frameworks (Co MOF@Au NPs) were synthesized through a facile two-step strategy, exhibiting excellent structural stability and catalytic activity toward the oxidation of TMB. Reactive oxygen species analysis confirmed that singlet oxygen (1O2) was the dominant reactive oxygen species involved in the catalytic process. Benefiting from the enhanced OXD-like catalytic performance and high substrate affinity of Co MOF@Au NPs, (specific activities of 34.32 U/mg), a competitive colorimetric aptasensor was prepared using aptamer-functionalized magnetic beads as capture probes and cDNA-modified Co MOF@Au NPs as signal probes. In the presence of TC, probes could release lead to a concentration-dependent colorimetric response. Under optimal conditions, the sensor achieved a wide linear range (60-240 nM) and a low detection limit (18.09 nM), while demonstrating excellent selectivity against common interferents. Furthermore, the practical applicability of the sensor was validated in milk samples with high recovery rates, offering a reliable and cost-effective approach for monitoring antibiotic residues in food safety applications.