Highly sensitive electrochemical DNA sensor based on the use of three-dimensional nitrogen-doped graphene

This paper describes a voltammetric method for sensitive determination of specific sequences of DNA. The assay is based on three-dimensional nitrogen-doped graphene (3D–NG) which, due to its excellent electrical conductivity, provides a favorable microenvironment to retain the activity of immobilized probe single-stranded DNA and also facilitates electron transfer. The free-standing 3D–NG electrode was characterized by scanning electron microscopy, Raman and X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. Differential pulse voltammetry was applied to monitor DNA hybridization using Methylene Blue as an electrochemical indicator. Under optimal conditions, the peak currents (best measured at 0.28 V vs. Ag/AgCl) increase linearly with the logarithm of the concentrations of ssDNA in the 10 f. to 10 nM concentrations range, with a 3.5 f. detection limit (at a signal/noise ratio of 3). The biosensor exhibits good selectivity for ssDNA and can distinguish even single-base mismatches. The capability of the method was tested with spiked serum samples, and excellent reproducibility and stability is found. This indicates that the strategy is promising for use in clinical applications.