Blue light enhances background current and dopamine sensitivity of carbon-fiber microelectrodes during fast-scan...

Electrochemical measurements of neurotransmitters in tissue are often made in conjunction with optogenetic and fluorescent techniques which expose the electrode to light. Recently, our lab observed that light affects the background current of electrodes, but this effect has not been systematically characterized. Here, we investigate the effects of blue and green-light exposure on carbon-fiber microelectrodes (CFMEs) using fast-scan cyclic voltammetry (FSCV). The effects of light on background charging current were observed at three potentials: near the switching potential of the dopamine waveform (1.2-1.3 V), at the dopamine oxidation potential (0.6-0.7 V), and at a lower potential (0.2 V). When exposed to blue light, the largest change in background current appeared near the switching potential both during calibration and also in tissue. The background change was 50% less with green light, and the largest change was still at the switching potential. Then, we exposed CFMEs to light for 1 minute and detected dopamine. CFME currents for dopamine were enhanced after blue-light exposure during calibrations and there was a 33% increase in the current for electrically stimulated dopamine in mouse nucleus accumbens core (NAcC) brain slices. We hypothesize that this enhancement is generated by photothermal effects that shrink the width of the electric double layer and alter analyte adsorption thermodynamics. Thus, to account for the effects of light in FSCV experiments, the light should be turned on 30 s before the experiment, calibrations should be performed with light for tissue experiments, and more red-shifted wavelengths should be used when possible.