Covalent linking DNA to graphene oxide and its comparison with physisorbed probes for Hg2+ detection

Graphene oxide (GO) has attracted extensive research interest as a platform for DNA adsorption and biosensor development. While most researchers use simple physisorption of fluorescently labeled DNA, covalent sensors are less susceptible to non-specific probe displacement and minimize false positive results. In this work, three thymine-rich DNA probes of different lengths are modified on their 3'-end with an amino group for covalent conjugation to GO. They also each contain an internally labeled fluorophore so that Hg2+ binding can lead to a large distance increase between the fluorophore and the GO surface for fluorescence signaling. Hg2+-dependent fluorescence signaling from the covalent sensors are compared with that from the non-covalent sensors in terms of sensitivity, selectivity, signaling kinetics, and continuous monitoring. The covalent sensors are much more stable and resistant to nonspecific probe displacement, while still retaining high sensitivity and similar selectivity. The detection limits are 16.3 and 20.6 nM Hg2+, respectively, for the covalent and non-covalent sensors, and detection of spiked Hg2+ in Lake Ontario water is demonstrated. (C) 2015 Elsevier B.V. All rights reserved.