Graphene and its precursor in the chemical route synthesis, the graphene oxide (GO), are excellent candidates for electrochemical biosensing applications, due to its conductivity properties, good biocompatibility and various functionalization possibilities. The crucial development of GO-related electrochemical applications lies in the design of simple and reliable assembly routes for the preparation and functionalization of Gr and GO-based electrodes. Fine control over assembly conditions is responsible for the range of novel properties exhibited by these kinds of sensing platforms.
Following the above stated issues, we proposed to study how the immobilization strategies used to attach GO and GO functionalized with chitosan (CHIT) to Au electrodes affect the electrochemical/interfacial properties and protein loading of the resulting platforms. For this purpose, commercially available GO was used. The functionalization of GO with CHIT was performed with the aid of EDC/NHS coupling agents and the reduction of GO-CHIT was performed with NaBH4 and further confirmed through IR and Raman Spectroscopies and H1-NMR.
The voltamperometric and impedance response of redox markers ferricyanide, H2O2 and hydroquinone provided the electrochemical information in each step of the platform modification. Oxidation current of H2O2 and hydroquinone decreased after the GO-CHIT and CRGO-CHIT covalent immobilization while in the case of non-covalent assembly strategies, it increased. These results, combined with SEM and surface plasmon resonance (SPR) measures over Au disks, showed that the covalent strategy provided the lowest degree of grapheneous material loading over the Au modified surface.
Scanning electrochemical microscopy (using ferrocenemethanol as redox mediator) also provided evidence of different kinds of local conductivity of Au/MPS/PDDA/GO, Au/MPS/GO-CHIT and Au/MPS/CRGO-CHIT platforms, being the latter the one that has the best conductivity due to restoration of the sp2 graphene network.
The different spatial arrangements of GO and CRGO in covalent and non-covalent strategies also strongly influence the sensibility of the Au modified platform to the blocking of the surface when BSA was linked. This step is critical taking into account that the platform is going to be used to attach an antibody for the development of an electrochemical immunosensor.
