# Nanomaterials for Healthcare Biosensing Applications
## 3 Applications of Inorganic Nanomaterials in Healthcare Biosensing  
Transitional metals and noble metals display extraordinary properties at the nanoscale. The excess surface atoms coupled with incompletely filled penultimate or pre-penultimate orbitals give rise to unique quantum effects and optical properties. They can not only form good alloys but can also be used in combination with various organic and carbon-based materials to form nanocomposites, exhibiting a combination of different characteristics or entirely new qualities [2]. Inorganic nanomaterials may possess different anisotropies, such as triangular, spherical, and nanohole [133]. They appear in different forms, such as bimetallic alloys, core-shell structures, metal organic framework (MOFs), nanotube, and nanowire arrays [56; 67; 71]. Each of these nanomaterials is capable of enhancing the biocompatibility and transduction characteristics of biosensors with the help of appealing interface and surface features. They may act as immobilisation platforms, enhance refractive index changes, catalyse reactions between substrates and chemiluminescents, magnify mass changes, and accelerate electron transfer [134; 135; 136; 137; 138; 139; 140; 141; 142]. In electrochemical sensors, such nanoparticle platforms may also act as electron wires apart from immobilisation, and thus transduce the biomolecular physicochemical changes to quantifiable signals. Some inorganic nanomaterials, such as Fe\({}_{3}\)O\({}_{4}\), demonstrate a magnetic nature and can be easily manipulated by an external magnetic field, allowing simple extraction and buffer replacement, and also provide a high signal-to-noise ratio in biological samples, in addition to their large surface area [143; 144; 145; 146]. They can be used for homogenising, trapping, enriching, transporting, and labelling of analytes, especially in POC testing. They can be applied for microfluidic mixing, which is crucial to lab-on-chip biosensing. Most magnetic nanoparticles (MNPs) consist of a magnetic core of pure elements (like Co and Fe), alloys (like FePt), or iron oxides (such as maghemite \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) or Fe\({}_{3}\)O\({}_{4}\)). This core is generally coated with inorganic [147] or polymeric [148] molecules, which act as sites for biofunctionalisation. Embedding multiple MNPs in a non-magnetic matrix may result in superparamagnetic behaviour [2; 143]. Novel inorganic architectures such as nanoshells, nanocages, and nanowires have recently gained much attention for biosensor development. Nanoshells, usually comprising a dielectric silica core enveloped in a highly conducting, ultrathin layer of silver or gold, constitute a new class of nanomaterials with tunable plasmon resonance, permitting materials to be particularly engineered to match the wavelength for specific applications, such as near infrared (NIR) areas where optimal light penetration through tissue is required [2; 149]. Nanoshell substrates with surface enhanced Raman spectroscopy (SERS)-based sensors are promising platforms for in vivo detection [150; 151; 152]. Nanocages are nanostructures with hollow interiors and porous walls, usually made of noble metals [69; 153]. Due to their high surface area, they show great potential for bio-functionalisation and biomolecule immobilisation. One-dimensional (1D) nanowires typically possess a length:diameter ratio above  
Figure 7: Scheme depicting sensing mechanism using f-GNPItts-GNDs: (**a**) graphitisation of nanodiamonds, (**b**) urea hydrolysis in presence of urease, (**c**) sensor fabrication and urea detection [121]. 1000 and may be semiconducting or dielectric in nature. They exhibit unique electrical and thermal properties. Noble metal nanowires demonstrate localised SPR (LSPR)-like properties that can be tuned according to their thickness [154; 155; 156]. Nanowire arrays can penetrate cellular lipid bilayers like nanoneedles, enabling cytosensing and similar medical diagnostic uses. Silicon oxide NW can act as a substrate for receptor immobilisation in FET biosensors [2; 155].