Adhesive-backed polyimide tape (Radionics, 70 m, HB830) was drawn and affixed to clean glass slides, ensuring no air bubbles were trapped. The polyimide top surface was converted to laserinduced graphene by CO2 laser (10.6 m, 30 W, Universal Laser system, PLS4.75) raster patterning at 4.2 W average laser power, ∼200 mm s -1 scan speed (1000 pixels per inch, PPI) and ∼20 lines mm -1 raster line density. Smooth edges were defined by a vector write (3.7 W average laser power, ∼200 mm s -1 scan speed and 1000 PPI), yielding two parallel rectangular carbon electrodes (10 mm X 3 mm) separated by ∼100 m.