Advanced fast-scan cyclic voltammetry techniques for dopamine measurement

Abstract

Dopamine (DA) plays an essential role in the central nervous system by modulating a variety of brain circuitries. An imbalance in DA extracellular level is known to be relevant to many disorders such as depression, addiction, schizophrenia, and Parkinson’s disease. To understand the complexity of the native brain including such disorders, analytical methods need to be involved. Fast-scan cyclic voltammetry (FSCV) with carbon-fiber microelectrodes (CFMs) has been widely used to measure neurochemicals such as DA because of its high sensitivity, chemical selectivity, and superior spatial and temporal resolution relative to other in vivo neurochemical monitoring techniques. Conventional FSCV has been used to measure phasic DA release in vivo by adopting a background subtraction procedure to remove background capacitive currents. Although FSCV has been utilized for detecting neurotransmitter in neuroscience research, there are several limitations for significant analytical analysis such as; pH transient, inherently unstable background capacitive currents, and any other changes that could affects CFMs surface. In the previous researches, we have reported FSCV technique to have better differential ability (Paired-pulse voltammetry) and its interpretation (DA reduction mechanism). In this thesis, three limitations of conventional FSCV is classified into three subjects; (1) FSCV is suffer from distinguish metabolites in mixture environment while maintaining high sensitivity, (2) Background subtracting reference point should be renewed every 2 minutes, which is unable to measure long-term change of DA, (3) the background subtraction method fundamentally inhibit FSCV from measuring tonic concentration. The work described within, the improvement of FSCV technique specifically designed to overcome those limitations based on previous findings. First, sawhorse waveform PPV with prolonged switching potential duration is suggested for both DA (Triangular shape) and 5-HT (N-shape). In both cases, the response of PPV to DA and 5-HT showed significantly increased while maintaining its high selectivity to other interferents. Second, charge-balancing multiple waveform fast-scan cyclic voltammetry (CBM-FSCV) is designed to measure slow change of DA tonic concentration over 2 hours in vivo (48 hours in vitro). By adopting charge-balancing waveform and dual background subtraction method, capacitive background current is minimized in temporal variations. The concept of multiple waveforms also enables high selectivity against 3,4-dihydroxyphenylacetic acid and ascorbic acid, two major chemical interferents in the brain. Lastly, tailoring FSCV is developed in substitution for conventional background subtraction method which is the prime hindrance for quantifying tonic DA concentration. By adjusting waveform voltage, corresponding voltammogram is matched with target voltammogram. While there are still DA signal difference, which is proportional to the tonic concentration of DA, background current can be eliminated without background subtraction. The work described within improves an advancement in neuro-analytical methodology that could be provided as an important method for studying fundamental chemical mechanisms of brain.