**6.4 Piezoelectric effect biosensor**

The term "piezoelectricity," sometimes known as "the piezoelectric effect," refers to a material's ability to produce voltage when physically stretched. The result also applies in the opposite circumstance. When applied to a piezoelectric material's surface, alternating voltage results in mechanical stress or oscillation. Piezoelectric materials typically have anisotropic crystals, or crystals without a center of symmetry. It does not require the application of any particular reagents and may easily capture affinity interactions, so the development of biosensors appears to be best suited to the piezoelectric platform. On the other hand, certain specific factors like fragility and the sensitivity in micrograms required to cause a detectable shift in oscillations should be taken into account.

Piezoelectricity is a powerful technique for building biosensors in analytical chemistry. Two electrodes deliver alternating voltage to excite the biosensor's surface, causing mechanical oscillations in a crystal. The frequency of these oscillations is measured when an analyte or mass is attached to the crystal's surface, specifically to the electrodes. This process allows for accurate measurement of the oscillation frequency.

Piezoelectric immunosensors are analytical tools that may be used to distinguish between various bacteria and macromolecules. Piezoelectric immunosensors use an antibody as a biorecognition component, with the specificity of the antibody determining the overall immunosensor's specificity. This ensures that the electrode and other sensitive parts of the piezoelectric material remain sensitive to unspecific interactions with chemicals. Although the reverse reaction is also conceivable, immunosensors typically include immobilized antibodies and can detect antigens. It means that the immunosensor may be used to identify an antibody and that the only molecule being examined is an antibody. Immobilized antigens may also be included in the immunosensor [28, 29].

Piezoelectric immunosensors are appropriate for analyte measurements that have large molecular weights as they lead to a significant reduction in oscillation frequency. The challenge of utilizing antibodies mounted on a piezoelectric substrate to directly

recognize small molecular weight analytes is another disadvantage of this method. Microorganisms are one type of analyte that piezoelectric immunosensors can specifically assess directly, and new models of piezoelectric immunosensors are frequently used to test these analytes [30–32].

Genetic data can be used as a biorecognition component in many biosensors. For the purpose of building biosensors, single-stranded, brief strains of DNA or RNA can be written down as typical instances of genetic information formats. The whole chromosomes, however, are also useful for tracking particular interactions. These biosensors frequently analyze human tissue or blood samples as well as genetic information from pathogens. The analyte and the biorecognition component of the biosensor, however, can be suggested as a potential pair since they interact with double-stranded DNA chains or immobilized chromosomes [33–36].

The diagnosis of disorders with a genetic basis is well optimized for the use of DNA biosensors. Promising studies in this area can be introduced through a few examples. Pang and colleagues made the decision to examine codon DC17 of the betathalassemia gene for point mutations. The hybridization of a DNA probe on gold nanoparticles and DNA from the sample served as the basis for the detection. The evaluated oligonucleotides had an assay limit of detection of 2.6 nmol/L, and the hybridization was carried out using a quartz crystal microbalance (QCM) sensor. Ye and coworkers disclosed using a combination of quantum dots and magnetic nanoparticles to identify DNA in an experiment [37, 38].

Lectins, a group of proteins with high carbohydrate content, are potential piezoelectric biosensors with high specificity to sugars. These proteins work in immunoassays like antibodies, requiring only the carbohydrate moiety for interactions. The D-mannose-binding lectin from jackfruit *Artocarpus heterophyllus* was used to recognize N-glycosylated receptors on leukemia-related hematopoietic cells as a biosensor [39–41].
