ELECTROSPUN NANOFIBERS FOR SENSORS

Electrospinning is one of the most important technologies for the preparation of micro/nanoscale continuous polymer fifibers. In general, conventional textile fifibers have a diameter of more than 5 mm, and the fifiber diameter obtained by melt or solution spinning is usually in the range of 500 nm to 5 mm, with the assistance of mechanical stretching. Electrospun fifibers, however, possess a diameter down to the submicrometer or even nanoscale, and the range is from 300 nm to 5 mm. Thus, it can be seen that electrospinning technology can signifificantly reduce the fifiber diameter, into the micro/nanoscale, and enhance the specifific surface area (SSA) to great advantage (Su et al., 2014, Long et al., 2012a,b). Furthermore, the raw materials can include a wide range of natural polymers, synthetic polymers, and inorganics. By adjusting the ratio of spinning solution, the spinning liquid composition, and the posttreatment process, and with the combination of multiple technologies, fifibers can be prepared with diverse properties. Consequently, electrospun nanofifibrous membranes (NMs) can be applied in fifiltration, catalysis, supercapacitors, lithium batteries, sensors, and tissue engineering, among others (Ding et al., 2015).

Among all the applications of NMs, sensors have always been one of the hot research topics. A sensor is a device that can be perceived, measured, and converted to usable output signals in accordance with certain rules. In some disciplines, sensors are also known as sensitive components, detectors, converters, and so on. These different formulations reflflect the use of different technical terms for the same type of device in different technical fifields, depending only on device usage. In the fifield of electronic technology, electronic components that can feel signals are often referred to as sensitive components, such as a thermal component, magnetic component, photosensitive component, and gas-sensing component. In most instances, the signal output is in a form of electricity, which is easy to transfer, convert, process, display, and so on (Mondal and Sharma, 2016). There are other kinds of signals, such as voltage, current, capacitance, resistance, etc., and those output signals guiding and determining the sensor designing principles. Frequently, the sensor consists of a sensing component and a transition component. The sensing component is the unit that can directly respond to the external stimulus; and the transition component is responsible for converting the stimulus into a signal portion,then suitable for transmission/measurement. Sensing response materials are at the core of the sensing component, as well as being the accurate components of the sensor, and from the sensor type to the sensing response material structure.

Since the 1990s, the rise of nanotechnology and nanomaterials has injected new vitality into the study of sensors. For the purpose of improving detection performance, some researchers attempted to introduce NMs into the confifiguration design of the sensing response material (Barkalina et al., 2014). It is noteworthy that sensing performance on one hand depends on the constituent parts of sensing component, and on the other hand depends on the material structure and geometric scale of the sensing component. When the scale of materials turns from the macro to the micro/nano level, consequential effects begin to signifificantly inflfluence sensing performance, such as small-scale effects, surface and interface effects, and quantum size effects, showing a number of characteristics that macroscales do not have. With the decrease in sensor size, the surface energy can be increased, and at the same time, the proportion of atoms on the material’s surface increases accordingly. When the surface atomic ratio is raised to a certain extent, the characteristics of sensors will be determined more by the surface atoms than by the internal lattice atoms. Furthermore, the increase in SSA provides a large number of areas and channels that enhance the interaction between the determinant and the NMs, and thus sensitivity is further improved. In addition, the use of NMs can reduce the energy consumption and the overall size of the sensor, thereby extending their service scope.

In this chapter, we will review recent progress in the development of NMs as a sensing response material and their applications in four predominant sensing schemes (electrochemical, optical, resistive, and mass-change-sensitive sensors), and illustrate them with examples showing how they have been applied and optimized. Moreover, we will also discuss their intrinsic fundamentals and optimal designs. Ultimately, we will highlight gaps requiring further research.

Paper link：https://www.sciencedirect.com/book/9780323512701/electrospinning-nanofabrication-and-applications