# Nanomaterials for Healthcare Biosensing Applications
## 4 Organic Nanomaterial Applications for Healthcare Biosensing
### Dendrimers  
Dendrimers are molecular nanoparticles with a covalent assembly of atoms distinguished into three architectural components [2]: (i) a central core of initiator or metallic ions; (ii) generations representing interior layers of repeating units bound to the core (Figure 12); (iii) terminal functionality representing the exterior of the particle which is attached to the outermost generation of the interior layers. The multifunctional interface in addition to their globular ship makes dendrimers potential candidates for fabricating hybrid, multilayer nanomaterials. One of their most interesting virtues is the ability to self-assemble into superstructures at material peripheries. Their unique structural features, such as hyperbranching, spheroidal surface, nanoscopic size, and voluminous interior, in addition to high solubility, fluidity, and reactivity, have made dendrimers one of the newest classes of macromolecular sensing devices for medical diagnosis [3]. Although analytes such as proteins and dendrimers readily attach to inorganic biosensor surfaces, they may lose their activity due to denaturation. An interesting strategy to avoid this phenomenon is the immobilisation of dendrimers on the biosensor surface [251]. A similar strategy for the immobilisation of streptavidin on PAMAM functionalised GCE was performed using electrostatic interactions upon drop coating of the electrode in the study of Soda and Arotiba [252]. An electrochemical interrogation of the GCE-G3(PAMAM)-Str proof-of-concept DNA biosensor was performed in phosphate buffer, H\({}_{2}\)O\({}_{2}\)  
Figure 11: (**a**) Multi-functional nanogel capable of drug storage, temperature sensing, cell imaging, and drug delivery [245], (**b**) Ring opening reaction of rhodamine B derivative induced by Hg\({}^{2+}\) ions [246]. Figure 12: (**a**) First-generation (G1) dendrimer, (**b**) second-generation (G2) dendrimer. and ferrocyanide. The stable, electroactive supramolecular architecture of the dendrimer-streptavidin platform acted as a versatile substrate for the immobilisation of any biotinylated receptors. Erdem et al. functionalised MNPs with G4 PAMAM dendrimers to achieve improved voltammetric sensing of DNA oligonucleotide (DNA-ODN) upon electrode response [253]. G4 PAMAM with a core of 1,4-diaminobutane was used to functionalise the streptavidin coated MNPs. The geomagnetic assay obtained by voltammetric detection had an LOD of 4.09 \(\upmu\)mL\({}^{-1}\). Hao et al. developed a microfluidic _E. coli_ O157:H7 sensor using a combination of aptamers and dendrimers [254]. They established the superiority of seventh-generation (G7) PAMAM dendrimers over G4. The aptamer-dendrimer modification on the plasma-treated poly(dimethylsiloxane) (PDMS) surface furnished multiple binding sites to boost target capture at high throughput rates. The efficacy of the sensor was evaluated with fluorescent measurements and a low LOD of 10\({}^{2}\) cells mL\({}^{-1}\) with a wide linear response of 10\({}^{2}\)-10\({}^{7}\) cells mL\({}^{-1}\) was obtained. Elencheziyan and Senthilkumar encapsulated G3 PAMAM dendrimers with haemoglobin (Hbg) immobilised AuNPs for sensing H\({}_{2}\)O\({}_{2}\) electrochemically [255]. CV and amperometric responses provided a linear response for the concentrations between 20 and 950 \(\upmu\)M with 6.1 \(\upmu\)M as the limit. Shukla et al. reported an electrochemical urea biosensor consisting of zirconia (ZrO\({}_{2}\)) and G2 poly(propylene imine) (PPI) dendrimers co-deposited on an SPCE with the help of CV [256]. The amperometric sensor could determine urea in the range of 0.01-2.99 mM. The G2(PPI) acted as a biocompatible nanolayer encapsulating ZrO\({}_{2}\) and played the role of a covalent attachment site. Borisova's group developed a new nanohybrid using G4 PAMAM with magnetic PDA nanoparticles decorated with platinum nanoparticles (PtNPs) [257].