In recent years, researchers have discovered the potential of using biocompatible materials as electronic components. Gelatin, a natural protein obtained from animal bone and skin, is one such substance that exhibits useful dielectric properties for these applications. In the paper by Zhuang et al., the researchers used gelatin as a component in an organic thin-film transistor (OTFT) creating a device that may function as an ammonia sensor for air pollution monitoring.
The authors explained that the development of ammonia sensors made from OTFTs has focused on improving the organic semiconductors in the device. These devices are often plagued by high power consumption. According to this report, changing the transistor architecture by adding a layer of gelatin as a gate dielectric on an OTFT platform allowed the measurement of ammonia concentrations as low as 174 parts per billion (ppb) with an applied voltage of -4 volts.
To better understand the mechanism for this high sensitivity, the authors also tested a similar, but different, design that included a layer of polystyrene between the gelatin and the OTFT. This comparison device was less sensitive to ammonia, and the polystyrene deteriorated the transistor function, raising the operating voltage to -40 volts.
AFM studies described in this work showed that the gelatin and gelatin/polystyrene systems had similar morphologies, so the authors concluded that it is unlikely that film roughness is a dominant factor in the observed sensitivity differences. Further studies with X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy revealed a number of polar functional groups on the gelatin. These groups could potentially absorb and trap ammonia, but might be out of reach if a polystyrene film composed of benzene rings blocks the OTFT from the gelatin layer. This could explain the enhanced sensitivity of the new device.
Source: “Biocompatible and degradable gelatin dielectric based low-operating voltage organic transistors for ultra-high sensitivity NH3 detection,” by Xinming Zhuang, Dayong Zhang, Xiaolin Wang, Xinge Yu, and Junsheng Yu, Applied Physics Letters (2018). The article can be accessed at https://doi.org/10.1063/1.5054026.