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.

Automated summary

We introduce a novel method called pulsed femtosecond laser-induced two-photon oxidation (2PO) to locally adjust the sensitivity of solution gated graphene field-effect transistors (GFETs) without damaging the carbon network of chemical vapor deposition (CVD) grown graphene. By using 2PO, the sensitivity of GFETs reached (25 +/- 2) mV pH(-1) in BIS-TRIS propane HCl (BTPH) buffer solution, corresponding to an oxidation level with a Raman peak intensity ratio I(D)/I(G) of 3.58. The sensitivity of non-oxidized, residual PMMA contaminated GFETs was 20-22 mV pH(-1). Initially, the sensitivity decreased to (19 +/- 2) mV pH(-1) (I(D)/I(G) = 0.64) due to the removal of PMMA residue by laser irradiation. Through 2PO, the functionalization of CVD-grown graphene with oxygen-containing chemical groups can be locally controlled, leading to improved performance of GFET devices. The GFET devices were made HDMI compatible to facilitate their connection with external devices and enhance their applicability.