# Nanomaterials for Healthcare Biosensing Applications
## 4 Organic Nanomaterial Applications for Healthcare Biosensing
### Nanostructured Films  
To fabricate sensors for detecting various parameters in a biological environment, it is essential for all the biosensor components to be biocompatible. The materials should be nontoxic and recalcitrant to bodily fluids and tissues. Concomitantly, it should also not prompt chronic or acute response from tissues or cause inflammation. To this end, nanolayers or polymeric nanofilms provide an efficacious solution due to their protective nature, in addition to being used as sensing mediums wherein the refractive index of a nanolayer is changed due to an alteration in the quantity of the measurement variable [3]. Nanostructured films can act as an ideal transducing element capable of transferring the stimuli from the analyte as well as facilitating covalent functionalisation. Exploiting this virtue of nanofilms, Rahmanian and Mozaffari deposited ZnO-poly(vinyl alcohol) hybrid films on an FTO electrode to develop an enzymatic urea biosensor. The impedimetric biosensor utilised the hybrid films as transducers and harnessed the hydroxyl groups from polyvinyl alcohol (PVA) for the covalent immobilisation of the urease enzyme. The electrostatic repulsion from the nanofilm hindered the binding of anionic interferents. CV and EIS measurements provided a detection limit of 3.0 mg dL\({}^{-1}\) with a linear response between 5.0 and 125.0 mg dL\({}^{-1}\)[233]. Enzymes and, generally, proteins are important structured elements that have found applications in biosensing [234]. Another class of promising sensing elements is based on carbohydrates or glycopomers [235]. A representative example of nanostructured films as an impedimetric element for bio-recognition was reported by Kraatz [236]. Forming a film of transmembrane glycoproteins called toll-like receptors (TLR) on a flat conductive surface results in effective sensors that recognize molecular patterns or signatures of pathogens. TLR specifically reacts with lipopolysaccharideacharide (LPS) endotoxin, which is a glycolipid located at the outer membrane of Gram-negative bacteria. Applying EIS, the limit of detections found for _E. coli_ and _Salmonella_ were \(1.3\times 10^{-4}\) and \(1.5\times 10^{-4}\) EU mL\({}^{-1}\), respectively. Pedro et al. were the first to develop intrinsically conducting polymer (ICP) nanofilms as fluorescence quenchers for DNA sensing [227]. They performed a comparative study between PPy and polyaniline (PAni) nanofilms on a polyethylene terephthalalate (PET) substrate. The biomarker was 6-carboxyfluorescein-labeled single-stranded DNA (FAM-ssDNA) from _Leishmanian intimatum_ (_L. infantum_) parasite. The thickness and hydrophobicity of the films resulted in a high signal-to-noise ratio. The detection limit for PAni/PET was 1.3 nM, whereas for PPy/PET it was 1.1 nM. Another similar study using electrodeposited ICP utilised CV to deposit a Nafion nanostructured poly(aniline) (PAni) film for the ultrasensitive detection of creatinine(CRN), a common biomarker for nephrological diseases [237]. The film promoted electron transfer and acted as a substrate for creatinine deaminase (CRND) immobilisation. The amperometric sensor achieved a detection range of 0.005-0.4 mM and the LOD was 0.005 mM. Phetsang's group fabricated an amperometric biosensor using nanocomposite film of Pt, RGO, and P3 ABA deposited on an screen printed carbon electrode (SPCE) for the enzymatic detection of glucose and cholesterol [238]. The nanofilm modified electrode showed exceptional electrocatalytic oxidation for H\({}_{2}\)O\({}_{2}\) and the LOD and detection ranges for glucose were 44.3 uM and 0.25-6.00 mM, respectively. The detection limit for cholesterol was found to be 40.5 uM within a detection range of 0.25-4.00 mM. Another study with a much lower cholesterol LOD fabricated a similar nanofilm-based cholesterol sensor using PDA nanofilm structured with PB and oxidised MWCNTs [239]. The PDA film promoted ChsOx immobilisation. The sensor showed a high affinity for cholesterol.