Low Voltage Operating Field Effect Transistors with Composite In₂O₃–ZnO–ZnGa₂O₄ Nanofiber Network as Active Channel Layer

Field effect transistors (FETs), incorporating metal-oxide nanofibers as the active conductive channel, have the potential for driving the widespread application of nanowire or nanofiber FETs-based electronics. Here we report on low voltage FETs with integrated electrospun In₂O₃–ZnO–ZnGa₂O₄ composite fiber channel layers and high-K dielectric (MgO)_0.3-(Bi_1.5Zn_1.0Nb_1.5O₇)_0.7 gate insulator and compare their performance against FETs utilizing conductive single phase, polycrystalline ZnO or In₂O₃ channel layers. The polycrystalline In₂O₃–ZnO–ZnGa₂O₄ composite fibers provide superior performance with high field effect mobility (∼7.04 cm²V^–1s^–1), low subthreshold swing (390 mV/dec), and low threshold voltage (1.0 V) combined with excellent saturation, likely resulting from the effective blocking of high current-flow through the In₂O₃ and ZnO nanocrystallites by the insulating spinel ZnGa₂O₄ phase. The microstructural evolution of the individual In₂O₃, ZnO, and ZnGa₂O₄ phases in composite fibers is clearly observed by high resolution TEM. A systematic examination of channel area coverage, ranging from single fiber to over 90% coverage, demonstrates that low coverage results in relatively low current outputs and reduced reproducibility which we attribute to the difficulty in positioning fibers and fiber length control. On the other hand, those with ∼80% coverage exhibited high field effect mobility, high on/off current ratios (>10⁵), and negligible hysteresis following 15 sweep voltage cycles. A special feature of this work is the application of the FETs to modulate the properties of complex polycrystalline nanocomposite channels

Selective Detection of Acetone and Hydrogen Sulfide for the Diagnosis of Diabetes and Halitosis Using SnO₂ Nanofibers Functionalized with Reduced Graphene Oxide Nanosheets

Sensitive detection of acetone and hydrogen sulfide levels in exhaled human breath, serving as breath markers for some diseases such as diabetes and halitosis, may offer useful information for early diagnosis of these diseases. Exhaled breath analyzers using semiconductor metal oxide (SMO) gas sensors have attracted much attention because they offer low cost fabrication, miniaturization, and integration into portable devices for noninvasive medical diagnosis. However, SMO gas sensors often display cross sensitivity to interfering species. Therefore, selective real-time detection of specific disease markers is a major challenge that must be overcome to ensure reliable breath analysis. In this work, we report on highly sensitive and selective acetone and hydrogen sulfide detection achieved by sensitizing electrospun SnO₂ nanofibers with reduced graphene oxide (RGO) nanosheets. SnO₂ nanofibers mixed with a small amount (0.01 wt %) of RGO nanosheets exhibited sensitive response to hydrogen sulfide (<i>R</i>_air/<i>R</i>_gas = 34 at 5 ppm) at 200 °C, whereas sensitive acetone detection (<i>R</i>_air/<i>R</i>_gas = 10 at 5 ppm) was achieved by increasing the RGO loading to 5 wt % and raising the operation temperature to 350 °C. The detection limit of these sensors is predicted to be as low as 1 ppm for hydrogen sulfide and 100 ppb for acetone, respectively. These concentrations are much lower than in the exhaled breath of healthy people. This demonstrates that optimization of the RGO loading and the operation temperature of RGO–SnO₂ nanocomposite gas sensors enables highly sensitive and selective detection of breath markers for the diagnosis of diabetes and halitosis

Selective Diagnosis of Diabetes Using Pt-Functionalized WO₃ Hemitube Networks As a Sensing Layer of Acetone in Exhaled Breath

Thin-walled WO₃ hemitubes and catalytic Pt-functionalized WO₃ hemitubes were synthesized via a polymeric fiber-templating route and used as exhaled breath sensing layers for potential diagnosis of halitosis and diabetes through the detection of H₂S and CH₃COCH₃, respectively. Pt-functionalized WO₃ hemitubes with wall thickness of 60 nm exhibited superior acetone sensitivity (<i>R</i>_air/<i>R</i>_gas = 4.11 at 2 ppm) with negligible H₂S response, and pristine WO₃ hemitubes showed a 4.90-fold sensitivity toward H₂S with minimal acetone-sensing characteristics. The detection limit (<i>R</i>_air/<i>R</i>_gas) of the fabricated sensors with Pt-functionalized WO₃ hemitubes was 1.31 for acetone of 120 ppb, and pristine WO₃ hemitubes showed a gas response of 1.23 at 120 ppb of H₂S. Long-term stability tests revealed that the remarkable selectivity has been maintained after aging for 7 months in air. The superior cross-sensitivity and response to H₂S and acetone gas offer a potential platform for application in diabetes and halitosis diagnosis