A rapid biosensor for highly sensitive protein detection based on G-quadruplex-Thioflavin T complex and terminal protection of small molecule-linked DNA

Small molecule-protein interaction plays a prominent role in biological and clinical research. In this paper, based on Guanine (G)-quadruplex-thioflavin T (ThT) complex and terminal protection of small molecule-linked DNA, a simple and rapid biosensor for protein detection has been developed. This strategy was demonstrated by taking the streptavidin (SA)-biotin system as a model. In the presence of ThT, G-rich biotinylated ssDNA could transform to G-quadruplex structure and form G-quadruplex-ThT complex showing stronger fluorescence compared with free fluorogenic dye ThT. In the absence of SA, G-quadruplex was digested by exonuclease I (Exo I) to liberate ThT generating an extremely weak fluorescence signal. With the addition of SA, the specific binding between SA and biotin confirmed that G-quadruplex-ThT complex was protected against the degradation by Exo I, and the strong enhancement of the fluorescence intensity was observed. A linear correlation equation was obtained for SA from 0.05 to 2500 ng/mL with a low detection limit of 0.02 ng/mL. In addition, satisfactory results were obtained from detection of SA in 5% human serum.