A facile colorimetric aptamer assay for small molecule detection in food based on a magnetic single-stranded DNA binding protein-linked composite probe

Herein, a promising colorimetric strategy for small molecule detection was developed based on one novel magnetic single-stranded DNA binding protein (SSB)-linked composite probe. Firstly, a magnetic probe was synthesized by labeling SSB on gold magnetic particles (Au MNPs-SSB) and detection probe by co-immobilizing aptamer (Apt) and horseradish peroxidase (HRP) on the core-shell SiO 2 @Au nanoparticles (Apt-SiO 2 @Au-HRP); furthermore, Au MNPs-SSB was bound with Apt-SiO 2 @Au-HRP to construct a composite probe relied on the specific affinity between SSB and free aptamer. When the target, with chloramphenicol (CAP) as model, was introduced into the reaction system, the formation of the target-Apt-SiO 2 @Au-HRP complex can release from its parent probe to supernatant after magnetic separation because SSB can’t bind target-aptamer complex. The target-Apt-SiO 2 @Au-HRP complex in supernatant could efficiently catalyze 3,3′,5,5′-tetramethylbenzidine(TMB)-H 2 O 2 system for the color development. Under the optimized reaction conditions, the linear range was from 0.05 to100   ng   mL −1 with a low detection limit of 0.02   ng   mL −1 for CAP. Moreover, the aptamer assay was employed to detect CAP in milk and the results were consistence with those from ELISA. In addition, the assay can be easily extended to other small molecules detection when changing the corresponding aptamer on the detection probe.