Label-free aptamer biosensor for thrombin detection on a nanocomposite of graphene and plasma polymerized allylamine

A label-free and effective aptasensor based on an amino-functionalized nanocomposite of graphene and plasma-polymerized allylamine (G–PPAA) was developed for thrombin detection. Graphene was assembled on the substrate, followed by the self-assembly of octadecylamine (OTA) to protect the graphene from etching by subsequent plasma irradiation. Afterward, PPAA was deposited onto the graphene surface with the self-assembled OTA, and the nanocomposite with amino groups was fabricated. The label-free thrombin aptamer was immobilized onto the amino-functionalized nanocomposite matrix via electrostatic interaction between the phosphate groups of the aptamer and the amino groups in PPAA. The process was investigated using impedimetric detection and a quartz crystal microbalance (QCM). The chemical compositions, surface morphology, and electrochemical properties were found to be dependent on the plasma conditions used in the polymer deposition. The amounts and kinetics of aptamer immobilization and thrombin detection were determined using QCM measurements. A relatively high affinity constant of aptamer immobilization and low detection limit for thrombin were achieved by using the G–PPAA film as the biosensor matrix. Results suggest that G–PPAA films can be applied in gene therapy and protein detection.