Real Colorimetric Thrombin Aptasensor by Masking Surfaces of Catalytically Active Gold Nanoparticles

We presented a simple, cost-effective, and ultrasensitive colorimetric approach for visually detecting thrombin by the catalytic amplification of gold nanoparticles (AuNPs) and aptamer-thrombin recognition. Thrombin can be quantified in the presence of catalytic AuNP surface by using color-change time of 4-nitrophenol. Without thrombin, yellow 4-nitrophenol can freely access the surface of AuNP and becomes colorless 4-aminophenol. With the addition of thrombin, aptamer-thrombin with large size interaction masks the partial surfaces of AuNPs, and increases the reduction time of 4-nitrophenol to 4-aminophenol. The maximum number of bound thrombin fully mask the catalytic AuNP surface, and thus 4-nitrophenol cannot approach to AuNP surface, the color of the solution remains yellow. The limit of detection (LOD) of 0.1 nM can be achieved with naked eyes. Of note, the method was further applied for the detection of thrombin in human serum samples, showing the results in agreement with those values obtained in an immobilization buffer by the colorimetric method.