A reduced graphene oxide-Au based electrochemical biosensor for ultrasensitive detection of enzymatic activity of botulinum neurotoxin A

Botulinum neurotoxin serotype A (BoNT/A) is a type of neurotoxin which is able to cause fatal paralytic illness botulism in a low dosage. Therefore, there is a great need to develop an ultrasensitive bioassay to detect its active state for early diagnostics and prevention. This paper presents a reduced graphene oxide (rGO)/Au electrode based electrochemical biosensor for ultrasensitive detection of BoNT serotype A light chain (BoNT-LcA) protease activity. The fabricated rGO/Au electrode provides a robust and biocompatible platform with enhanced electron transfer capability and large area for peptide immobilization. SNAP-25-GFP peptide substrate is firstly immobilized on rGO surface via pyrenebutyric acid (PA) linker. The addition of BoNT-LcA could specifically cut SNAP-25-GFP at the cleavage sites to release the cut section from the electrode surface. This enzymatic activity of BoNT-LcA on SNAP-25-GFP peptide substrate could be detected by monitoring the enhanced redox probe transfer rate by differential pulse voltammetry (DPV) with a linear detection range from 1 pg/mL to 1 ng/mL and the limit of detection (LOD) for BoNT-LcA is around 8.6 pg/mL. The specificity of this biosensor is demonstrated with BoNT-LcB and heat-treated BoNT-LcA. Moreover, the experiments for BoNT-LcA detection in milk samples demonstrate the feasibility of this biosensor in complex matrix.