RESEARCH

The main theme of the project(s) in this research topic is to develop a more detailed and coherent understanding of the correlation of the brain chemical dynamics to brain function and structure, which is scarce at present. Specifically, the pathogenesis of epilepsy, TBI, Huntington’s Disease and dementia at the molecular level in terms of glutamate (Glu) uptake coupled with GABA synthesis, cellular metabolism, neuronal antioxidant (AO) capabilities and the production of reactive oxygen/nitrogen species. These are all very relevant for synapse function, energy metabolism and neurotransmitter (NT) homeostasis. Towards this goal, we will develop a highly multiplexed electrochemical probe that can measure the real-time extracellular changes in the levels of these brain chemicals implicated in neuropathology. The probe will employ unique fabrication techniques and surface modification approaches with enzymes, advanced carbon materials and polymers. The ultimate goal is to identify new biomarkers for new and more effective therapies. (A) Shows the calibration curves of glutamate (Glu) detection with various surface modifications. (B) Shows the calibration of 5 nM to 400 nM dopamine (DA) with various surface modifications.

REAL-TIME GLUTAMATE-GABA DETECTION EX VIVO

In this project, we designed and implementation a novel Glutamate (Glu)-GABA electrochemical microarray probe that operates on a newly conceived principle. It consists of two microbiosensors, one for Glu and one for GABA detection, modified uniquely with enzymes. By simultaneously measuring and subtracting the hydrogen peroxide oxidation currents generated from these microbiosensors, GABA and Glu is detected continuously in real-time and without the addition of any externally applied reagents. We further optimized the microsensors for the highest sensitivity and selectivity measurements that constitutes a novel and powerful neuroscientific tool that could be employed in the future for in vivo longitudinal studies of the combined role of GABA (a major inhibitory neurotransmitter) and Glu (a major excitatory neurotransmitter) signaling in brain disorders, such as epilepsy and traumatic brain injury, as well as in preclinical trials of potential therapeutic agents for the treatment of these disorders.

HYBRID DIAMOND-CARBON NANOTUBE MICROELECTRODES FOR CHEMICAL SENSING

In this project, we demonstrate the potential of a hybrid multiwall carbon nanotube (MWCNT) film modified boron-doped ultrananocrystalline diamond (UNCD) microelectrode for improved detection of dopamine (DA) in the presence of common interferents. A series of modified microelectrodes with varying film thicknesses were microfabricated by electrophoretic deposition (EPD). Using cyclic voltammetry, the 100-nm “thin” film microelectrode produced the most favorable combination of DA sensitivity value of 36 ± 2%µA/µM/cm2 with a linear range of 33 nM to 1 µM and a limit of detection (LOD) of 9.5 ± 1.2% nM. The EIS spectra of these microelectrodes revealed three regions with inhomogeneous pore geometry and differing impedance values and electrochemical activity, which was found to be film thickness dependent. Using differential pulse voltammetry, the modified microelectrode showed excellent selectivity by exhibiting three distinct peaks for the DA, serotonin (5-HT) and excess ascorbic acid (AA) in a ternary mixture. These results provide two key benefits: first, remarkable improvements in DA sensitivity (>125-fold), selectivity (>2000-fold) and LOD (>180-fold), second, these MWCNTs can be selectively coated with a simple, scalable and low cost EPD process for highly multiplexed microsensor technologies. These advances offer considerable promise for further progress in chemical neurosciences.

CONCENTRIC NANORING ELECTRODES (NRE) FOR INTRACELLULAR ELECTROCHEMICAL STUDIES

We report on the microfabrication and characterization of a gold nanoring electrode (Au NRE) patterned on top of a silicon (Si) micropillar. An NRE of 165 ± 10 nm in width was micropatterned on 4.6 ± 1 μm diameter × 17.5 ± 2.5 μm long Si micropillar with an intervening 50 nm thick hafnium oxide insulating layer. The electrochemical behavior of the Au NRE was characterized by a steady-state cyclic voltammogram with extremely high signal-to-noise ratios of 2500 and charging currents as small as 1.5 ± 0.3 pA. A “semicircle spectrum” from the Nyquist plot indicates a kinetically-controlled voltammetric current response, which is unique to nanoscale electrodes. The applicability of Au NREs to electrochemical sensing is demonstrated by detecting lead, a neurotoxin at 100 ppb levels. Also, by surface-modification with multi-walled carbon nanotubes, dopamine, a neurochemical implicated in various brain disorders, is detected at a sensitivity as low as 100 nM with 1000-fold selectivity versus common interferents. The flexibility of the microfabrication approach allows for the creation of multiple NREs of controllable width and nanometer spacing on a single micropillar. This capability and in particular where the NRE is micropatterned on three-dimensional microstructures as will be reported herein, facilitates unique electroanalytical capabilities such as intracellular electrochemistry and highly multiplexed detection for emerging biological applications.

ENGINEERING ROBUST DIAMOND ELECTRODES BASED ON ADDITIVE MANUFACTURING METHODS FOR ELECTROCHEMICAL WASTEWATER TREATMENT