# Nanomaterials for Healthcare Biosensing Applications
## 4 Organic Nanomaterial Applications for Healthcare Biosensing
### Hyperbranched Polymeric Nanoparticles  
Hyperbranched polymers (HBPs) are structurally similar to dendrimers but there are certain key distinctions. In addition to the dendritic cores and terminal units present in dendrimers, HBPs also contain linear units. Furthermore, the dendritic and linear units are distributed arbitrarily throughout the macromolecular architecture, giving rise to irregularities in the structure. As opposed to dendrimers, HBP synthesis generally involves a single step reaction [229]. Due to low chain entanglements, linearity, and a large number of functional groups, HBPs present interesting thermal, rheological, electrochemical, and luminescent properties, presenting enormous scope in different kinds of biosensing systems [259]. Niu's group developed a hyperbranched polyester to mimic heparin for thrombin detection [260]. The sulfonated HBP was functionalised on a GCE with the help of mercaptopropyltrimethoxysilane (MPTMS) and AuNPs prior to thrombin binding aptamer (TBA) immobilisation. The label-free aptasensor was also used for in vitro studies to develop hemolysis assays, platelet, and whole blood adhesion tests as well as to understand the changes in the morphology of red blood cells. Exceptional sensitivity was observed with an extremely wide detection range of 2.7 pM-27.0 \(\upmu\)M and a limit of 31 fM. In another study, human sirtuen 1 (SirT1), a molecule which has potential anti-aging properties, was successfully detected using cross-linked hyperbranched azo polymer (HAP) [261]. Initially, indium tin oxide (ITO) was coated with PDA and then dipped in an HAP-AuNP colloidal solution. Finally, the electrode was coated with cAb and BSA was used to block the free sites. A sandwich immunoassay was obtained using dAb in conjugation with a secondary antibody Ab\({}_{2}\) immobilised on a TiO\({}_{2}\)-AuNP nanocomposite. DPV provided linear electrochemical responses between 1.0 and 500 ng mL\({}^{-1}\) and the LOD was 0.28 ng mL\({}^{-1}\). A similar ultrasensitive CEA sandwich immunosensor using hyperbranched polyester for electrochemical detection was reported by Miao's co-workers [262]. This study was conducted using an ITO electrode, wherein hyperbranched 2,2-bis(hydroxymethyl)propionic acid DMPA was grafted to the surface modified to obtain carboxyl functionalised end groups. Subsequently, a cAb was immobilised on the electrode. An HRP-labelled AuNP with dAb was used as a signalling probe. A detection range between 0.01 and 80 ng mL\({}^{-1}\) was obtained with an LOD of 2.36 pg mL\({}^{-1}\). It is important to maintain adequate Cu\({}^{2+}\) levels in the body, as its deficiency can result in bone abnormalities and neutropenia, whereas its excess can cause damage to kidneys and the liver and may even prove fatal. Therefore, Wang et al. developed an optical sensor for Cu\({}^{2+}\) detection using hyperbranched polyethyleneimine (PEI) modified with formaldehyde and capped with AuNPs [263]. Detection was possible by visual evaluation as well as fluorescence and UV-visible spectroscopy techniques. The linear response at pH 4.0 was obtained in the 0.15-23 \(\upmu\)M concentration range and the LOD was 77 nM. Romero and co-workers exploited the self-assembly of hyperbranched 2,2-bis(methyl)propionic acid (bis-MPA) on the surface of MWCNT to a fabricate an amperometric sandwich-type lactate sensor [264]. A platinum electrode functionalised with the aforementioned 3D scaffolds was used as a matrix to wire lactate oxidase (LOx). The HBP(bis-MPA) reduced the elastic characteristics of the enzyme matrix, thereby bringing an increment in the diffusion coefficient. This resulted in a lower detection time due to in situ regeneration of the enzyme mediator (O\({}_{2}\)). The linear detection range was 0.9 \(\upmu\)M-1.5 mM and the limit was 0.9 \(\upmu\)M.  
Sedki's group developed a nanocomposite of reduced graphene oxide (RGO) with hyperbranched chitosan to develop sensor platform for monitoring cell viability [265]. The target bacterium was _P.