Super Nernstian pH response and enzyme-free detection of glucose using sol-gel derived RuO_x on PET flexible-based extended-gate field-effect transistor

In this paper, we fabricated a sol-gel derived RuO_x, with low-temperature thermal oxidation, on polyethylene terephthalate (PET) flexible based extended-gate field-effect transistor (EGFET) as a pH sensor for the assessment of glucose for the first time. Structural identification, surface morphology, and film composition of the sensing membrane were investigated by X-ray diffraction, atomic force microscopy, and X-ray photoelectron microscopy, respectively. The RuO_x on PET based EGFET sensor exhibited a pH sensitivity of 65.11 mV/pH in the wide range of pH 2–12 with an excellent linearity of 0.999. This sensor showed good reversibility in terms of a lower hysteresis voltage of ∼1 mV and a better stability for 12 h named as drift rate ∼2.08 mV/h. The RuO_x-based EGFET sensor also demonstrated a high selective response towards H⁺. In addition, the pH performace of this RuOx EGFET flexible sensor kept unchanged after 500 repeated bending cycles. Subsequently, the RuO_x on PET based EGFET was functionalized by 4-carboxyphenyl boronic acid (4-CPBA), which is a synthetic receptor for covalent attachment of glucose on the sensing surface. The sensitivity of glucose was 6.89 mV/mM with the linearity of 0.993 within the glucose concentration from 1 to 8 mM. The concentration of serum glucose measured by our 4-CPBA functionalized RuO_x EGFET biosensor is comparable to that determined by commercial blood glucose monitoring system. In addition, this RuO_x EGFET biosensor exhibited an elevated reference voltage shift response to glucose compared with other saccharides (e.g. fructose, sucrose and mannose).