  Because of high surface area and combination of various functional groups,
graphene oxide (GO) is currently one of the most actively studying materials
for electroanalytical applications. Self-supported GO is not practical enough
to be utilized individually and thus is commonly integrated with different
supporting carriers. Having large lateral size GO can only wrap the particles
of the support and thus, can significantly reduce the surface area of porous
materials. To reach synergy form high surface area and polyfunctional nature of
GO, and a rigid structure of porous support, the lateral size of GO must be
essentially decreased. Recently reported graphene oxide quantum dots (GOQDs)
can fulfill this task. We report successful preparation of mesoporous silica
supported GOQDs exhibiting strong luminescent band with the maximum at 404 nm.
From N2 adsorption isotherms, it was demonstrated that the surface area of the
resulted hybrid material was augmented. Raman spectrum of SiO2-GOQDs shows two
distinct peaks at 1585 cm-1(G-peak) and 1372 cm-1 (D-peak) indicating presence
ordered basal plane of graphene with aromatic sp2 domains, and disordered
oxygen-containing structure. Covalent immobilization of GOQDs on aminosilica
via such oxygen-containing fragments was proved by FTIR, MAS 13C MNR, and XPS
spectroscopy. SiO2-GOQDs was used as a modifier of carbon paste electrode for
differential pulse voltammetry determination of four environmental:
sulfamethoxazole, trimethoprim, diethylstilbestrol (DES), and estriol (EST).
The modified electrodes demonstrated an essential decrease in LOD for EST
(220%) and DES (760%), which was explained by significant pi-pi stacking
interaction between GOQDs and aromatic system of the analytes.
