▎ 摘　　要

A graphene oxide-Au NPs sensor platform combined with a multiple-enzyme labeled detection antibody-carbon sphere bioconjugate has been used as the basis for an ultrasensitive electrochemical immunosensor to detect the cancer biomarker, a-fetoprotein (AFP). Greatly enhanced sensitivity has been achieved by using the bioconjugates featuring horseradish peroxidase (HRP) and Ab2 linked to carbon nanospheres (Ab2-HRP-Au-PDA-carbon sphere) at a high ratio of HRP/Ab2. After a sandwich immunoreaction, the Ab2-BRP-Au-PDA-carbon sphere captured onto the electrode surface produces an amplified electrocatalytic response due to the reduction of enzymatically oxidized thionine in the presence of hydrogen peroxide. The increase of response cm-rent is proportional to the AFP concentration in the range of 0.01-20 ng/mL, with the detection limit of 3 pg/mL. This amplification strategy is a promising platform for detection of other proteins and clinical applications.