# Application of Organic-Inorganic Hybrids in Chemical Analysis, Bio- and Environmental Monitoring
## 3 Biosensors as a Targeted Class of OIH  
Biosensors are portable devices, able to selectively detect target biomolecules in low concentration range in the presence of a complex matrix (serum, blood, saliva, food samples, fermentation media, etc.). Biosensors enable the conversion of biological functions (e.g., antigen-antibody interactions) into signal read-outs (e.g., change in optical, or electrical properties). This biosensor's feature enables a wide range of practical applications from environmental monitoring to nanomedicine. The development and tailoring of new materials are important issues to develop novel biosensors with advanced properties. Large surface area, porosity, topography, and enhanced surface functionality can significantly improve the sensing properties of the hybrid material and strengthen the interaction between surface and adsorbate (bioanalyte) [59, 60, 61]. The use of nanostructured hybrid materials and/or nanocomposites for the development of biosensors, in this case nanobiosensors, gives the possibility to achieve higher analyte sensitivity and device miniaturization. In recent years, researchers have investigated nano-based OIH (OInH) because of their new properties and applications they demonstrated. Generally speaking, all biosensors are a class of OIH because of the organic or bio-recognition elements (aptamers, antibodies, DNA/RNA etc.,) presented on the biosensor surface. Biosensors can be prepared by means of different methods, i.e., drop casting and covalent immobilization [62, 63, 64, 65]. Also, a conventional layer-by-layer (LbL) deposition methodology is widely utilized. The LbL fabrication approach offers a superior versatility toward production of the OIH assemblies, including polymer, colloids, and biomolecule coatings [66]. However, in some cases the manufacturing of LbL-enzymatic biosensors involves a number of complex, resource and time-consuming preparation steps. In addition, LbL assays are often suffering from mechanical instability that leads to insufficient signal reproducibility and irreversible changes in sensor architecture. In order to solve the problems associated with the LbL preparation method, recently a novel one-step technique was proposed for the production of tailored enzymatic nanobiosensors that are instrumentally controlled and allow reproducible, spatial, and temporal resolution, simultaneous multi-analyte detection with high specificity [67]. However, it should be noted that regardless of the fabrication method, the general guidelines towards validation of the OIH in general, as well as towards  
Figure 3: The workflow of boron nitrides (BN)-gelatin nanofiber synthesis. Adapted and reproduced with permission from. Reproduced with permission from [56], Copyright American Chemical Society, 2017.  
standardization of biosensors and nanob biosensors as a case study are still under development (see section below titled \"The role of nanoanalytics and nanometrology in OIH development\"). As previously defined, a biosensor is an analytical device that includes a combination of biological detecting elements and a transducer. Depending on the transducer's signal (electrical, optical, mechanical etc.,) and biological recognition element (DNA, enzyme, antibody, molecular imprinted polymer etc. ), one may classify biosensors into different types. For instance, an electrochemical immunosensor means that this biosensor is based on antibody as a recognition element, and in this device linear (I-V), cyclic voltammetry (CV) signal, or electron impedance spectroscopy (EIS) are used. OIH biosensors based on surface enhanced Raman spectroscopy (SERS) are broadly used in biomedicine applications. SERS is a very sensitive method in which monochromatic laser light excites vibrational modes in adsorbed molecules on a plasmon surface [59]. For instance, a poly(3,4-ethylenedioxythiophene) (PEDOT)-based 3D-OECT device decorated with gold nanoparticles (Au-NPs), as a SERS substrate, has been developed for the detection of dopamine (DA) [68].