Neurobiological use of a micro-optrode using UV excitation light and signal-to-noise ratio optimization

μMany fluorescent tools have been developed through the past decades in order to better understand the physiology at a cellular level. They are generally used for microscopy or endoscopy, in vivo and in vitro, but they are also usable with fluorescent sensors such as fiber optic sensors. Among these tools, fluorescent ion indicators have been widely used to understand ionic dynamics into living cells. Indicators are mainly designed for Ca²⁺, although K⁺ is also an important target for its role in maintaining cellular membrane potential and regulating many other electrophysiological phenomena. Here we propose a technique to improve the use of a miniature fiber optic sensor to sense potassium dynamics in vivo. Due to the lack of commercially available potassium indicators, we are using a UV excitable indicator (PBFI). The UV excitation light induces unwanted fluorescence and/or luminescence from the optical components including the sensing fiber, leading to a poor signal-to-noise ratio. Our technique uses a UV diode pumped Q-switched source from CrystaLaser, a time gated acquisition system and a delay fiber that improve the signal-to-noise ratio and allow reducing the sensor size and the light intensity provided to the tissue, thus diminishing UV induced photodamage. Using this technique we have been able to record intracellular potassium fluctuations in vivo with fiber optic sensors of 10μm diameter.