# Electrospinning-Based Carbon Nanofibers for Energy and Sensor Applications
## 4 Application of Carbon Nanofibers
### Sensor Applications
#### 4.2.3 Biosensor  
A biosensor is a type of sensor that can detect harmful bio elements, which can affect the health of the studied target. One of the most popular detection methods is to use a type of antibody or an aptamer as the key for the sensing mechanism, which provides the sensor with excellent selectivity and high sensitivity. To attach the antibody or aptamer to the material surface, carboxyl or nitrile functional groups are required in the structure of the material. [PERSON] et al. successfully functionalized the CNFs by stirring in a 30% nitric acid solution (Figure 20a) [143]. The results suggested that the treatment did not affect the diameter of the CNFs. When a detecting target binds to the antibody, it changes the surface resistance between the material and the electrolyte, which can be measured by  
Figure 19: (**a**) CNFs carry quantum dots for diethyl chlorophosphate fluorescent detection [138]. (**b**) Cactus-like CNFs with Ni nanoparticles for detection of DMMP [140]. (**c**) Cactus CNFs modified with HFIP for DMMP sensor [141]. (**d**) CNFs/CuO/Co\({}_{3}\)O\({}_{4}\) with silicone coupling agent and HFIP for DMMP detection [142].  
electrochemical impedance spectroscopy (EIS). The device can detect PSMA and ELISA with detection limits of 22.1 pg mL-1 and 9.5 ng mL-1, respectively.  
[PERSON] et al. used an attached aptamer for the detection of the platelet-induced growth factor (PDGF-BB) (Figure 20b) [144]. By introducing copper (Cu) into carbon fiber, the extra carbon layer could be grown on the Cu surface through chemical vapor deposition (CVD) with methane gas as a carbon source. After the Cu etching process, the CNFs had a 3D nanoweb structure, which significantly improved the surface area of the carbon material. Finally, the material was fabricated into a field-effect transistor with the screen printing of silver paste. The detection was carried out with a voltammetry measurement, and the device could operate with a detection limit of 1.78 fM with high selectivity. Moreover, the transistor can distinguish between the three types of PDGF; the BB type showed the largest change in current, the response to the presence of the AB type was smaller, and the AA type showed no response.  
[PERSON] et al. used Co3O4 and DPV measurements to detect the concentration of dopamine (DA) (Figure 20c) [145]. Before the electrodeposition of Co3O4, the CNFs were doped with a nitrogen function group using an 8 M nitric acid solution. Although the acid treatment played a role in reducing the material surface resistance, the presence of Co3O4 improved the electrocatalysis of the carbon electrode. The DPV data also showed that the material can distinguish DA from ascorbic acid and uric acid, which have similar redox properties. The peak of DA in the DPV curve appears to be much higher than the others even though the concentration is lower. The limit of detection from the material appears to be 9 nM with a wild dynamic linear range, indicating the CNFs excellent sensitivity and fast-charge transport.  
[PERSON] studied the effects of electrodeposition in the process of electrode preparation on the performant of the carbon electrode in the detection of DA (Figure 20d) [146]. The authors used electrodeposition to attach the porous CNFs to a bare carbon electrode. While keeping the waveform parameter unchanged, the change in the deposition time can affect the oxidation peak current. A specific deposition time (30 s) showed significant results  
Figure 20: (**a**) CNFs treated with nitric acid as working electrode material for PSMA sensors [143]. (**b**) 3D nanoweb CNFs as channel material for PDGF\(-\)BB detecting transistors [144]. (**c**) CNFs decorated with Co3O4 for detection of DA [145]. (**d**) CNFs deposited on carbon electrodes for DA detection [146].  
compared to longer deposition times. The prepared electrode has outstanding sensitivity and selectivity and can be reused up to 25 times.