Immobilized Enzymes in Biosensor Applications

Enzyme-based biosensing devices have been extensively developed over the last few decades, and have proven to be innovative techniques in the qualitative and quantitative analysis of a variety of target substrates over a wide range of applications. Distinct advantages that enzyme-based biosensors provide, such as high sensitivity and specificity, portability, cost-effectiveness, and the possibilities for miniaturization and point-of-care diagnostic testing make them more and more attractive for research focused on clinical analysis, food safety control, or disease monitoring purposes. Therefore, this review article investigates the operating principle of enzymatic biosensors utilizing electrochemical, optical, thermistor, and piezoelectric measurement techniques and their applications in the literature, as well as approaches in improving the use of enzymes for biosensors.

STRUCTURAL AND PIEZOELECTRIC PROPERTIES OF (1 − x)PZT-xBFN (x = 0.1 – 0.2) SOLID SOLUTION

The structural, dielectric and piezoelectric properties of (1 − x) PbZr 0.52 Ti 0.48 O 3– xBaFe 0.5 Nb 0.5 O 3 ceramic system with the composition near the morphotropic phase boundary were investigated as a function of the BaFe 0.5 Nb 0.5 O 3 content by X-ray diffraction (XRD), dielectric measurement and piezoelectric measurement techniques. Studies were performed on the samples prepared by solid state reaction for x = 0.10, 0.12, 0.14, 0.16, 0.18 and 0.20. The XRD analysis demonstrated that with increasing BFN content in (1 − x) PZT −x BFN , the structural change occurred from tetragonal to the mixture of tetragonal and cubic phase. Changes in the dielectric behavior and piezoelectric properties were found to relate with these structural changes depending on the BFN contents.

Microstructure and Characteristics of PbTiO3-PbZrO3-Pb(Mg1/3Nb2/3)O3- Pb(Zn1/3Nb2/3)O3 Ceramics

The new piezoelectric ceramic of PbTiO3-PbZrO3-Pb(Mg1/3Nb2/3)O3 -Pb(Zn1/3Nb2/3)O3 with composition close to the morphotropic phase boundary was studied. The dielectric and piezoelectric properties of Pb0.96Sr0.04[(Zr1-yTiy)0.74(Mg1/3Nb2/3)0.20(Zn1/3Nb2/3)0.06]O3 were investigated, the composition range examined are 0.47 £ y £ 0.57. From the results of XRD and piezoelectric measurement, it is supposed that the composition with y = 0.51 corresponds to M.P.B. between tetragonal and pseudocubic perovskite. Some developed phenomena or models are introduced and take it to interpret well. After optimal choice of these conditions, the planar coupling factor close to 0.65, mechanical quality factor Qm close to 75, the longitude wave velocity close to 4100 m/s and the poled dielectric constant close to 2600 can be approached in this study.

Enhanced Piezoelectric Properties of Barium Titanate Single Crystals by Domain Engineering

Engineered domain configuration was induced into barium titanate (BaTiO3) single crystals, and the d33 piezoelectricity was investigated as a function of domain size. Prior to the domain engineering, the dependence of domain configuration on the temperature and the electric-field was investigated, and above Curie temperature (Tc), when the electric-field over 16 kV/cm was applied along [111]c direction, the fine engineered domain configuration appeared. On the basis of the above information, the 33 resonators with different domain sizes were successfully prepared. Their piezoelectric measurement revealed that the d33 of the 33 resonators with fine-engineered domain configurations were higher than those of BaTiO3 single-domain crystals. Moreover, d33 increased with decreasing domain sizes. The highest d33 of 289 pC/N was obtained in the BaTiO3 crystal with a domain size of 13μm.