A novel colorimetric aptasensor for sensitive tetracycline detection based on the peroxidase-like activity of Fe 3 O 4 @Cu nanoparticles and "sandwich" oligonucleotide hybridization.

A novel colorimetric aptasensor has been developed for highly sensitive tetracycline (TC) detection based on the peroxidase-like activity of Fe 3 O 4 @Cu nanoparticles and "sandwich" oligonucleotide hybridization. The Fe 3 O 4 @Cu nanoparticles with high peroxidase-like activity were successfully synthesized under mild conditions. Then, a "sandwich" oligonucleotide hybridization probe (a short amino-modified complementary sequence of a portion of the TC aptamer (cDNA1), TC aptamers, and a long complementary to 5' terminal TC aptamer sequence (cDNA2)) was created in 96-wells plates via DNA hybridization in the absence of TC from the detection system. The unique "sandwich" oligonucleotide hybridization probe adsorbed large numbers of Fe 3 O 4 @Cu nanozymes while further enhancing its peroxidase-like activity. Based on the 3,3',5,5'-tetramethylbenzidine (TMB)-hydrogen peroxide (H 2 O 2 ) reporting system, the blue color of the solution decreased linearly with the increase of TC concentration, ranging from 10 -3 to 10 3  μg/L with an ultralow limit of detection (LOD) of 0.91 ng/L (2 pM). The proposed method was successfully applied to detect TC in spiked milk samples, with recoveries of 81.8 to 112%, demonstrating the excellent potential for highly sensitive TC detection in milk.