Ultrasensitive dopamine detection of indium-zinc oxide on PET flexible based extended-gate field-effect transistor

With the aim of a simple, label-free, and highly specific dopamine detection, we proposed an indium-zinc oxide (InZnxOy) sensing film on flexible PET using a simple sol-gel method for an extended gate field-effect transistor (EGFET) sensor. In this study, X-ray diffraction, atomic force spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the structural, morphological, and chemical features, respectively. The InZnxOy based EGFET sensor showed a super Nernstian pH response of 61.53 mV/pH with an excellent linearity of 0.995 (in the range of pH 2–12), a low hysteresis voltage of ∼ 3 mV (in the pH loop of 7→4→7→10→7) and a small drift rate of 3.52 mV/h (in the pH 7). Correspondingly, to investigate the impact of mechanical bending on the pH performances of InZnxOy based flexible EGFET sensor, a couple of bending tests, which include different bending radius and bending cycles, were performed. The device showed better mechanical durability up to 1500 bending cycles for pH sensitivity. In order to achieve the label-free detection of dopamine, the InZnxOy on PET-based EGFET was functionalized using a synthetic receptor named 4-carboxylphenylboronic acid, for the covalent binding of dopamine on the sensing surface. The sensitivity of dopamine is 10.69 mV/log(dopamine) with linearity 0.998 within the dopamine concentration range of 1 fM–1 nM and the limit of detection value is 0.523 fM. In addition, this InZnxOy based EGFET biosensor showed excellent selectivity to dopamine over other interfering chemicals. Our proposed InZnxOy EGFET biosensor was successfully applied to detect dopamine level in the real samples like rat blood serum and rat brain.