Optimizing nitrogen incorporation in nanodiamond film for bio-analyte sensing

Nitrogen incorporated nanodiamond electrodes were fabricated using microwave plasma enhanced chemical vapor deposition. The N2 incorporation was achieved by the introduction of N2 gas along with H2 and CH4 gases in the plasma. In the context of this work, the H2:CH4 ratio was held fixed at 9:1 and the N2 content was varied. Three different levels of N2 incorporation were examined: 30 sccm (S1), 60 sccm (S2) and 90 sccm (S3). The Fe(CN)63−/4− redox couple in 0.1 M KCl was used for initial evaluation of the electrochemical properties of the 3 electrodes. Cyclic voltammetry was then used to study the detection of dopamine (DA), which is an important neurotransmitter, in 0.1 M phosphate buffered saline (PBS) at the physiologic pH of 7.4. Electrode S1, which has a microstructure resembling that of ‘ridges’, showed excellent electrochemical response as compared to the other two electrodes, S2 and S3 which exhibited sluggish reaction kinetics. Cyclic voltammograms from S1 show well defined and closely spaced redox peaks, not only for dopamine, but also for its redox active metabolites which are produced due to reactions downstream of DA oxidation. The calibration curves for the three electrodes show linear behavior but S1 shows superior sensitivity towards DA detection. Also, a linear relationship between the DA concentration and √scan rate was observed which is consistent with semi-infinite linear diffusion limited mass transport mechanism for planar electrodes. These results have been achieved without the need of functionalization or modification of the electrode surface, using optimum N2 incorporated nanodiamond electrode.