# Electrospun Nanofibers for Integrated Sensing, Storage, and Computing Applications
## 3 Electrospun Nanofibers in Transistors: Computation and Multifunctional Electronics
### Typical Applications of Nanofiber-Based Transistors  
Even though development is mainly focused towards promoting the process and technique for field-effect transistors with the nanofiber active layer to obtain more stable and reliable devices, several applications have emerged to demonstrate the value of introducing electrospinning to the fabrication of FETs. Preliminary gas and humidity sensing, light-emitting devices, and basic logic circuit successively show up, caused by the special feature of better homogeneity, more porosity, stronger mechanical strength, and larger surface areas. In 2011, the single PANI nanofiber field-effect transistor produced by near field electrospinning (Figure 13a,b) first appeared and this gas sensing transistor offered tunable sensitivity and excellent signal-to-noise ratio with applied field effect [80]. Compared with traditional polymer film and CNT FET sensors, this sensor had higher sensitivity (7% versus 1 ppm of NH\({}_{3}\)), greater reliability, and requires much less energy. The main gas sensing mechanism of the PANI nanofiber was the deprotonation of PANI by NH\({}_{3}\), which caused a resistance rise. The response of this FET to the NH\({}_{3}\) gas with varying concentrations can be seen in Figure 13c. Moreover, a field-effect transistor could be used to boost the sensitivity of a humidity sensor in an appropriate gate voltage region. For example, a kind of Ga-doped ZnO nanostructure transistor (Figure 13d) was fabricated and its voltage region was in the positive range because of its n-type semiconducting nature [81]. When the environmental relative humidity (RH) changed between 15% and 85%, the current response of the FET (I\({}_{\text{ds}}\)) changed accordingly, and cyclic behavior and consistency in its functionality were explicit in this way (Figure 13e). Low cost and flexible one-dimensional light-emitting transistors represent another potential application for nanofiber-based devices. As early as 2010, a single nanofiber transistor made by the light-emitting polymer poly(2-methoxy-5-(2-ethylhexoxy)-1,4-phenylenevinylene (MEH-PPV) (Figure 13f) was prepared and it exhibited controllable photoluminescence intensity through applied bias [82]. As shown in Figure 13g-j, the intensity of photoluminescence (PL) from single fibers within FETs can be electrically manipulated in a luminist mode, reducing by a factor of 1.5 when the gate voltage (V\({}_{\text{GS}}\)) is varied from 0 to \(-\)40 V. Textile-based OFETs containing PQT-12:PEO nanofibers also showed superior photosensitivity under wavelengths of 470 nm compared to those under 670 nm, indicating that they might be used as photosensors with targeted wavelength detection [66] (Figure 13k,l). Further photo-sensing study for this FET was performed using a 10 \(\times\) 10 photodetector array and a star-shaped pattern achieved using a laser source can be exactly recognized with this high resolution, fabricated, textile-based device (Figure 13m,n). Besides the form capability of sensing, electrospun nanofiber-based FETs can act as chemical sensors. For instance, at an unprecedentedly low concentration of 1 fM of the Bisphenol A(BPA), a field-effect transistor sensor using aptamer-modified multichannel carbon nanofibers (MCNFs) to detect the chemical showed remarkable sensitivity and specificity for BPA [83] (Figure 14a,b). It was also proven that an MCNFs FET sensor responds directly in seconds when exposed to BPA. Furthermore, typical and simple logic circuits are realized by electrospun nanofiber-based transistors, and their fundamental application of building blocks for hardware circuit implementation to execute complicated computation offers these kinds of transistors great opportunities to truly reform the future integrated circuits. For instance, FETs based on ZnSnO nanofiber mat were connected in series with a 2 M\(\Omega\) external resistor to create a resistor-loaded inverter [13].