# Application of Organic-Inorganic Hybrids in Chemical Analysis, Bio- and Environmental Monitoring
## 3 Biosensors as a Targeted Class of OIH
This developed OECT/SERS biosensor featured a highly conductive PEDOT: PSS film, which enhanced the sensitivity for the electrochemical sensing of DA in the presence of multiple interferers, such as ascorbic (AA) and uric acids (UA). This biosensor provided an amperometric response to DA with a detection limit of 37 nM in the linear range from 50 nM to 100 \(\upmu\)M.  
[PERSON] et al. have developed the tin oxide (SnO\({}_{2}\))-cellulose hybrids by adopting liquid phase deposition technique and applied it for the detection of urea at low concentration level. The growth of SnO\({}_{2}\) nanocoating on the polymer films was revealed [69]. Furthermore, the enzyme (urease) was immobilized into this nanocomposite by physical absorption. The limit of detection for proposed urea biosensors was below a 50 mM concentration. An electrochemical sensor based on self-doped polyaniline (SPAN) modified metal-organic framework (SPAN@UIO-66-NH\({}_{2}\)) with high electron mobility was developed. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) indicated that doping of SPAN enhanced the electron transfer rates of UIO-66-NH\({}_{2}\) in SPAN@UIO-66-NH\({}_{2}\). The optimized design of a Cd\({}^{2+}\) sensor exhibited good linear response from 0.5 \(\upmu\)g L\({}^{-1}\) to 100 \(\upmu\)g L\({}^{-1}\), with a low detection limit of 0.17 \(\upmu\)g L\({}^{-1}\) (based on S/N = 3), excellent stability, and fast response. It showed decent reliability for detection of trace Cd\({}^{2+}\) concentrations in natural lake and urine samples [70]. Among different types of biosensors, optical biosensors become more attractive for end-users because of their small dimensions, low weight, and portability. Furthermore focusing on optical biosensors, these devices do not require electric contacts and demonstrate high precision in measurements [71]. Among a number of different inorganic materials, ZnO is well-known and interesting because of its structure (different architectures i.e., nanoparticles, nanowires, etc.,), electrochemical (high isoelectric point (IEP) (pH-9.1)) and optical properties (high exciton binding energy and high PL at room temperature) [72; 71]. Nanoscale ZnO materials offer many advantages for the development of novel biosensing platforms. 1D ZnO nanomaterials (ZnO nanorods and nanowires) have been intensively employed for in vitro biomedical detection (Figure 4) [2; 72]. The unique optical properties of 1D ZnO nanostructures have led to extensive development and their integration with optoelectronics and nanophotonics. However, the full potential of 1D ZnO nanomaterials in biosensing have not been realized up to now because of some difficulties in linking ZnO with surface biofunctionalization. Polymer surface functionalization is considered to be the most promising to solve this drawback. Below, one may find several examples to illustrate the state-of-the-art based on polymer surface functionalization. Thus, polydopamine (PDA) is a mussel-inspired polymer which was initially introduced by [PERSON] et al. in 2007 [73]. Since that time, it has found a lot of applications in material chemistry, nanoscience, and bioengineering [74]. Because of the presence of several reactive groups the PDA structure enables further biomolecule immobilization for biosensors construction, as well as for the development of different biosensing interfaces, viz., glucose oxidase, sulfate-reducing bacteria orinterleukin-6 and human immunoglobulins introduced into/onto the polymer matrix through cross linking [74; 75]. Interestingly, besides the intact PDA, ZnO-modified PDA nanostructures (ZnO/PDA) were used in biosensors [76; 77]. Briefly, ZnO nanorods, deposited on conductive glass, were coated with PDA. Furthermore, a targeted protein (rabbit IgG) was immobilized on the surface of ZnO to form biosective layer. Photoelectrochemical tests of the ZnO/PDA toward anti-rabbit IgG showed good sensitivity in the range 100 pg/mL to 500 ng/mL.