Colorimetric determination of the activity of methyltransferase based on nicking enzyme amplification and the use of gold nanoparticles conjugated to graphene oxide

A method is described for the colorimetric determination of the activity of CpG methyltransferase (M.SssI). It is based on (a) the crosslinking effect between dsDNA-modified gold nanoparticles (AuNPs) and graphene oxide (GO), and (b) an amplification reaction with the aid of a nicking enzyme. To avoid the aggregation of AuNPs (which would produce false signals), a hairpin DNA was connected to the AuNPs. Thus, the red color of the solution (measured at 530 nm) increases linearly with the activity of M.SssI from 0.2 to 60 U·mL−1, and the limit of detection is 67 U·mL−1. This is superior to some reported strategies. The method was successfully applied to analyze spiked serum samples. Conceivably, it represents a powerful tool for use in drug development and diagnosis.