A novel electrochemical aptasensor based on arch-shape structure of aptamer-complimentary strand conjugate and exonuclease I for sensitive detection of streptomycin.

Detection and quantitation of antibiotic residues in blood serum and animal foodstuffs are of great significance. In this study, an electrochemical aptasensor was developed for sensitive and selective detection of streptomycin, based on exonuclease I (Exo I), complimentary strand of aptamer (CS), Arch-shape structure of aptamer (Apt)-CS conjugate and gold electrode. The designed aptasensor inherits characteristics of gold including large surface area and high electrochemical conductivity, as well as high sensitivity and selectivity of aptamer toward its target, property of Arch-shape structure of Apt-CS conjugate to act as a gate and barrier for the access of redox probe to the surface of electrode and the function of Exo I as an enzyme which selectively digests the 3'-end of single stranded DNA (ssDNA). In the absence of streptomycin the gate remains closed. Thus, the electrochemical signal is weak. Upon addition of streptomycin, the Apt leaves the CS and binds to streptomycin and the Arch-shape structure is disassembled. Then, Exo I addition leads to a strong electrochemical signal. The designed electrochemical aptasensor exhibited high selectivity toward streptomycin with a limit of detection (LOD) as low as 11.4nM. Moreover, the developed electrochemical aptasensor was successfully used to detect streptomycin in milk and serum with LODs of 14.1 and 15.3nM, respectively.