Label-free fluorescent aptasensor of Cd2+ detection based on the conformational switching of aptamer probe and SYBR green I

Abstract A label-free fluorescence aptasensor based on conformational switching of aptamer induced by Cd2+ was established for the good selective determination of Cd2+. The aptamer could act as a recognition element for Cd2+. SYBR green I (SG), as a signal reporter, can bind to the small groove of double-stranded DNA (dsDNA) constituted the aptamer and the complementary strand, establishing the dsDNA-SG complex and generating high fluorescence intensity. In the presence of Cd2+, the specific recognition and binging of aptamers preferentially with Cd2+ induce free of complementary strands from dsDNA and conformational switching of aptamer from dsDNA to a stem-loop structure, fluorescence intensity of system decrease dramatically. Under the optimum experiment parameters, the aptasensor shows a good linear range from 1.12 μg L−1 to 224.82 μg L−1 and the excellent detection limit as low as 0.34 μg L−1. The relative standard deviations (RSD) for determination of Cd2+ (n = 8) were lower than 4%, and the recoveries were in the range of 98.57% ~ 102.49%. The use of fluorescence aptasensor has good selectivity and does not require any sample treatment or target preconcentration for the detection of Cd2+ in real samples.