Vertical silica nanochannels supported by nanocarbon composite for simultaneous detection of serotonin and melatonin in biological fluids

Herein we report the simultaneous determination of serotonin (5-HT) and melatonin (MT) by using highly ordered and vertically-oriented mesoporous silica-nanochannel films (VMSF) on highly electrochemically reduced graphene oxide-carbon nanotubes (HErGO-CNT) composite substrate. Such VMSF/HErGO-CNT with compact 2D–2D layered structure is fabricated on indium tin oxide (ITO) electrodes via a two-step electrochemical process, namely the electrodeposition of ErGO-CNT film onto the ITO surface by cyclic voltammetry and subsequently growth of VMSF on the ErGO-CNT/ITO surface by electrochemically assisted self-assembly method, during which graphene oxide (GO) is subjected to the two-time electrochemical reduction to form HErGO. The CNT encased in the GO sheets served as electronic conducting wires, which not only can promote the electrochemical reduction of GO but also contribute to a certain degree of hydrophobicity, facilitating the controllable electrodeposition of ErGO-CNT composites on ITO under its safe use potential window. In addition, doping CNT is able to enlarge the layer gap between graphene sheets and thus improves the electroactive area and mass transfer of the nanocarbon composite substrate. Furthermore, the underlying HErGO-CNT acts as an efficient electroactive layer and the outer VMSF possesses electrostatic preconcentration and anti-fouling functions, synergistically realizing the direct electrochemical analysis of 5-HT and MT in two complex biological fluids (human whole blood and artificial cerebrospinal fluid).