Adsorption of zwitterionic dopamine on GO. Theoretical study

NICOLÁS DOMANCICH; ANA ROSSI; LORENA MEIER; FUENTE SILVIA A; N. CASTELLANI

Santa Fe

Congreso; VI San Luis Conference; 2018

UNlitorlal

Dopamine (DA) is a neurotransmitter that plays an important physiological role in the humans and mammalians centralnervous, renal and hormonal system. The detection of its zwitterionic form (ZDA) at serum pH it is of great importance, and among the proposed sensors, field effect transistors (FET) have been evaluated, where graphene (G) or graphene oxide (GO) are used as materials for the gate of the FET. These materials have been shown to be very sensitive to adsorbed molecules.In the present work, the GO stability is theoretically studied and the adsorption of ZDA on the latter substrate is analyzed. The calculations were based on the DFT formalism and were implemented by means of the Vienna Ab-initio Simulation Program (VASP)1,2. For a coverage of 10% epoxy groups, it was observed that the proposed random configuration is more stable when the central epoxy group is located on the opposite side of G sheet. This behavior was not evident for the similar configuration with hydroxyl groups. Su et al.3 studied the GO stability with two epoxy groups on the same face and observed the following stability order: Para> Armchair> Zigzag [3]. In this work, the results indicate that by rearranging the structure with epoxy groups in Para and Zigzag dispositions, an improvement in energy is achieved.In addition, the adsorption of ZDA on GO was analyzed. The geometries studied correspond to different approaches of the ZDA to the epoxy or hydroxyl groups of GO. The presence of several of these groups per unit cell was also considered. The adsorption energy turns out to be exothermic and of greater magnitude than in the case of regular G system. The amino group of ZDA close to the epoxy originates a hydroxyl group, losing an H atom. Similar results were obtained in the presence of a hydroxyl group, in this case forming one water molecule. In all cases an electronic transfer from the molecule to the substrate is produced.