Highly sensitive impedimetric aptasensor based on covalent binding of gold nanoparticles on reduced graphene oxide with good dispersity and high density

A series of gold nanoparticles (AuNPs) that were covalently bound to 2-aminothiophenol-functionalized reduced graphene oxide (Au-ATP-rGO) composites have been synthesized with well-dispersed and controllable surface coverage of AuNPs. Aptamer immobilization capacity studies demonstrated that the surface density of AuNPs played a key role in increasing the amount of anchoring aptamers to enhance the sensitivity of affinity based detection. With the composites possessing dense surface coverage of AuNPs as a versatile signal amplified platform, a label-free aptasensor for the sensitive and selective detection of small molecules (ochratoxin A in this case) has been developed using electrochemical impedance spectroscopy (EIS). A wide linear range of 0.1-200 ng mL(-1) was obtained with a low detection limit of 0.03 ng mL(-1) (S/N = 3). This work provides a universal strategy for the sensitive detection of a variety of targets in a truly label-free manner by means of changing the corresponding aptamer. The promising platform based on the combination of Au-ATP-rGO composites, EIS technique, and aptamers would have great potential applications in clinical diagnosis, environmental analysis, and food safety monitoring.