Abstract
In this study, ultrasensitive pH sensing is achieved by charge-coupling with an amorphous(a)-InGaZnO-based thin film transistor (TFT) for use as an ultrasensitive biosensor. To enhance the detection sensitivity using the charge-coupling circuit, an extended-gate a-InGaZnO-based TFT sensor is employed, in which the size of the extended electrode with an oxide film is fixed but the channel size is controllable. The pH sensitivity was enhanced to 313 mV/pH at 25°C, above the ideal potential limit, by decreasing the channel size of the charge-coupling extended-gate TFT, although an insulated-gate TFT showed a standard pH response near the ideal Nernstian potential (59.1 mV/pH at 25°C) because of the non-charge-coupling gate structure. This is because ionic charges at an extended electrode with an oxide film, which are unrelated to the Nernstian interfacial potential, affect the channel conductivity of the TFT, in addition to the Nernstian interfacial potential. A platform based on the charge-coupling extended-gate a-InGaZnO-based TFT is suitable for an ultrasensitive and flexible biosensing system to monitor not only pH but also biomarkers such as glucose in sweat on skin in the future.
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