Laser-induced tuning of graphene field-effect transistors for pH sensing

Here we demonstrate, using pulsed femtosecond laser-induced two-photon oxidation (2PO), a novel method of locally tuning the sensitivity of solution gated graphene field-effect transistors (GFETs) without sacrificing the integrity of the carbon network of chemical vapor deposition (CVD) grown graphene. The achieved sensitivity with 2PO was (25 ± 2) mV pH^-1 in BIS-TRIS propane HCl (BTPH) buffer solution, when the oxidation level corresponded to the Raman peak intensity ratio I(D)/I(G) of 3.58. Sensitivity of non-oxidized, residual PMMA contaminated GFETs was 20-22 mV pH^-1. The sensitivity decreased initially by 2PO to (19 ± 2) mV pH^-1 (I(D)/I(G) = 0.64), presumably due to PMMA residue removal by laser irradiation. 2PO results in local control of functionalization of the CVD-grown graphene with oxygen-containing chemical groups enhancing the performance of the GFET devices. The GFET devices were made HDMI compatible to enable easy coupling with external devices for enhancing their applicability.