Long considered the key to creating complex devices that have functions determined by chemical synthesis, encoding functionalities in two-dimensional nanoscale components during chemical synthesis has always been considered. Graphene's unique mechanical properties, chemical inertness, and large surface have shown great promise for use as electrode materials to encode electronic functionality through chemical synthesis1. Due to its high cost and inability to easily make graphene conductive, the use of graphene remains limited.
We demonstrate in the current work a low-cost and simple method for making graphite electrodes (GDEs) conductors by immobilizing a methacrylic plastic on their surfaces. The resulting GDE is able to record highly sensitive cyclic voltametry results in aqueous and organic solutions with a potential window that matches that of commercial glassy carbon electrodes (GCEs). GDEs have also been shown to be functionalized via covalent bonding or surface adsorption. This shows their potential for applications like enzyme electrochemistry or bioelectrocatalysis.
GDEs with anti-inflammatory drugs diclofenac and nonimprinted polymers (NIPs) were functionalized. Both of these polymers were characterized by scanning electron microscopy, transmission electron microscopy and Brunauer-Emmett-Teller (BET) analysis, revealing that the MIP has cavities molded during the imprinting process. The GPUE-2.5 MIP was shown to have a sensitivity that is twice as great as compared with a non-modified GCE, and that is three times greater than the GPUE 2.5-NIP DCF that showed no molecule imprinting.
EIS tests were performed on 15% PE and 25 PE GDEs to determine their performance in the aqueous NaPi. The normal dependency of the peak current on the scan rate was observed, confirming that the electrodes are adsorption-controlled. EIS spectra showed, however, that 15% PE GDE had a strong diffusion limitation as shown by the Warburg line on the Nyquist graph.
In order to understand this phenomenon, the adsorption of the model compound L-cysteine on the GDEs was studied by coupled surface spectroscopy. In the S2p XPS area at 167 eV a peak of high intensity was found, suggesting a strong bond between the proteins and electrode surfaces. The S2p peak could not be observed in control experiments using pure graphite.
The GDEs exhibited a reversible response that was comparable to the commercial GCEs. The reversibility was lower for the GDEs with 25% PE due to reduced active sites available on the surface of these electrodes. This can be explained by the fact that the polymer methacrylic reduces the number of surfaces which are active. The degradation of the reversible potential with increasing concentration of analyte is a common result in adsorption-controlled electrodes. It could be due to the formation on the electrode surface of OH-groups, known to function as proton donor in the quinone radical reaction10. The immobilization as well as electrode functionalization results on GDEs demonstrate that these materials are capable of encoding electronic functionality and offer a variety of potential applications.
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