Principles of Dopamine Binding to Carbon Surfaces

Fast Scan Cyclic Voltammetry (FSCV) combined with carbon electrodes is considered as the gold standard method for real-time detection of oxidizable neurotransmitters. The bioinert nature, rapid electron transfer kinetics and long-term stability make carbon an attractive material for probing brain electrochemistry. Herein, we first demonstrate a rapid fabrication process of carbonized nanopipettes and subsequently perform experimental measurements and theoretical simulations to study mechanisms of dopamine binding on carbonized surfaces. To explain the kinetics of dopamine oxidation on carbonized electrodes we adapted the electron-proton transfer model originally developed by Compton and found that the electron-proton transfer model best explains the experimental observations. We further investigated the electron-proton transfer theory by constructing a Density Function Theory (DFT) for visualization of dopamine binding to graphite-like surfaces consisting of heteroatoms. For graphite surfaces that are capped with hydrogen alone, we found that dopamine is oxidized, whereas, on graphite surfaces doped with heteroatoms such as nitrogen and oxygen, we found deprotonation of dopamine along with oxidation thus validating our experimental and theoretical data. These observations provide mechanistic insights into multistep electron transfer during dopamine oxidation on graphite surfaces. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=186 SRC="FIGDIR/small/457508v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@8bee9corg.highwire.dtl.DTLVardef@de66ecorg.highwire.dtl.DTLVardef@1373032org.highwire.dtl.DTLVardef@3d61d0_HPS_FORMAT_FIGEXP M_FIG A: Pictorial view of the experimental setup of carbonized electrodes. The application of waveform causes the oxidation of dopamine. B. Background subtracted voltammogram of dopamine, wherein the waveform applied is -0.4V to 1.3V and cycled back at -0.4V at 200 V s-1 at 10 Hz. C: A hotspot showing the oxidation and reduction of dopamine, wherein two distinct redox spots can be seen. The first redox spot can be seen at 0.0V and the second one at 0.5V. Thus showing a multistep electron transfer for dopamine. D: A DFT model for dopamines interaction with graphite surfaces doped with nitrogen atoms. Oxidation of oxygen (red) can be seen with loss of protons. C_FIG