Fig. 5

a Diagram of the set-up inside a dark box for measuring the temperate of an illuminating LED in saline to use for calibration. The hotplate is to maintain 37 °C temperature and a thermometer monitors the temperature during the experiment; b experimental set-up to electrically characterize the circuits; c image of the experimental set-up inside the dark box; d image of non-encapsulated and encapsulated mini-LEDs employed in the experiments; and e close view of the optrode with illuminating LED dipped in water