## 4 Applications of Piezoelectric Materials in Analytical Chemistry
### Detection of Viruses  
Various viruses such as human papilloma, dengue virus, vaccinia, influenza A virus, Ebola virus, hepatitis B, and human immunodeficiency virus are detected by piezoelectric sensors. An alternating current causes a piezoelectric material to mechanically oscillate, creating an oscillating electrical field. The frequency regulated by alternating current voltage drops when the mass rises as a result of the molecular interactions. Piezoelectric sensors of the mass response type are frequently employed for the detection of viruses. Figure 28 provides a schematic representation of the piezoelectric biosensor's working. On the piezoelectric material's upper surface of the electrode, antibodies are attached. The piezoelectric material resonates as a result of the top and bottom electrodes. The majority of materials utilized for sensor materials are anisotropic, including PVDF, BaTiO\({}_{3}\), PbTiO\({}_{3}\), ZnO, AIN, and SiO\({}_{2}\)[134].  
Human papillomavirus is a potential cause of cervical cancer, the third-most frequent malignancy in women. [PERSON] et al. [135] created a piezoelectric gene sensor for the detection of the papillomavirus using an AT-cut quartz crystal of 10 MHz. Airborne detection and the rapid detection of the vaccinia virus were achieved using quartz crystal microbalance technology. By integrating the quartz crystal microbalance detection methods and polymerase chain reaction (PCR) amplification, [PERSON] et al. [136] produced a unique system for the detection of the vaccinia virus. Dengue fever is a widespread viral disease that is spread by mosquitoes and causes thousands of fatalities each year. It is a serious health issue in urban and semi-urban areas. A piezoelectric immuno-chip was created by [PERSON] et al. [137] for the detection of the dengue virus. They utilized a 10 MHz quartz crystal microbalance to detect dengue E protein and NS-1 protein using an 8 mm AT-cut quartz wafer sandwiched between the Au electrodes. Since the discovery of the Ebola virus in 1976, thousands of individuals have died from the illness. The virus is transferred among humans via direct contact with the secretions, blood, other body fluids, or organs of the infected persons, as well as with the surfaces and materials that have been contaminated by these fluids. This virus is spread in humans from wild animals. For the quick detection of the Ebola virus, [PERSON] et al. [138] suggested a label-free sensing method that is based on the surface acoustic wave sensor. The sensor chips were created by utilizing wafers of LiTaO\({}_{3}\). The influenza virus is the most harmful and prevalent infection, which has a  
Figure 28: Piezoelectric material used for virus detection; (**a**) piezo-electric biosensor operating principle; graph of (**b**) voltage to time and (**c**) amplitude to frequency, during detection [134].  
high level of infectivity and mutagenicity. Type A virus is transmitted both from human to human and animal to human. For the purpose of detecting the influenza-A virus, [PERSON] et al. [139] devised and created a surface acoustic wave sensor with piezoelectric LiNbO\({}_{3}\) wafers coated with SiO\({}_{2}\), Figure 29a. Another of the most frequently encountered diseases around the world is infection with hepatitis B. Despite the fact that billions of individuals have the hepatitis virus, effective treatments and medications have still not been developed to treat chronic hepatitis-B infections. Using the micro-fabrication technology, [PERSON] et al. [140] created a piezo diaphragm-based immuno-assay chip to identify the anti-hepatitis B virus, Figure 29b. The results showed a detection limit of 0.1 ng/mL.