In this work,a simple and label-free ultrasensitive electrochemical aptasensor platform was proposed.In the presence of thrombin,the thrombin-binding capture probe(CP)preferred to form thrombin/aptamer complex that could block the access of the DNAzyme to the cleavage site so as to prevent hydrolysis.Compared with DNase I or other enzymes,this strategy was cost-effective,easy to handle,and less prone to nonspecific adsorption onto the microarray surface,which resulted in the low background signal and desirable selectivity.Furthermore,the presence of CP enabled auxiliary DNA 1(AD1)to hybridize with auxiliary DNA 2(AD2)on the gold electrode(GE)so as to self-assemble into three-dimensional(3D)DNA networks.Thus,the electrochemical signal,which was originated from the AgNPs deposited in the DNA skeleton owing to the high affinity between metal cations and DNA,was able to be remarkably amplified through the hybridization chain reaction(HCR)so as to improve the sensitivity of the analytical method.Moreover,the current signal could be further amplified to achieve the detection of thrombin with the linear range from 0.0001 to 50 nM and the detection limit of 0.046 pM.The proposed aptasensor showed high sensitivity and good selectivity to thrombin over other non-target proteins,providing a promising method for thrombin detection in human serum.Therefore,the electrochemical aptamer-based sensor platform may represent a good electrochemical amplification assay with high sensitivity and selectivity.