Fig. 1.

a GO dispersed in water at 2 mg mL⁻¹ as a stable pure GO ink. b A typical TEM image of the GO sheets. c Photograph of the as-prepared carbon-based hybrid ink. d A typical TEM image of the graphite carbon nanoparticles dispersed in the commercial pen ink. e SEM image of the ink-jet printed micro-electrodes. f Schematic diagram of a symmetric device with 12-interdigital fingers