# Nanomaterials for Healthcare Biosensing Applications
## 3 Applications of Inorganic Nanomaterials in Healthcare Biosensing
### Nanocages, Nanoshells and Nanowires
The sensor detected glucose in the 0.5-30 uM concentration range and the detection limit was 0.05 uM. Another study loaded GQDs on surface villous AuNCgs to develop an electrochemiluminescence device based on Au nanoflower functionalised paper working electrode (AuNFI-PWE) for the detection of CA-153 on the surface of MCF-7 cells [216]. The sandwich assay constituted primary antibodies immobilised on AuNFI-PWE as the sensing platform and the secondary antibody functionalised GQD-AuNCgs as signal probes. The surface structure of the NCgs facilitated electron transport and allowed a higher number of GQDs to be loaded. The rapid and low-cost device provided linear responses between 0.005 and 500 U mL\({}^{-1}\) with a good sensitivity (LOD: 0.0014 U mL\({}^{-1}\)). Nanoshells (NShs) are spherical nanoparticles which generally consist of a thin metallic outer shell with a dielectric core, as illustrated in Figure 10b [217]. NShs make ideal components for optical sensors, as their quantum plasma oscillation feature can be easily adjusted by manipulating the composition and size of the core and shell [218]. It is feasible to functionalise biomolecules, such as proteins, on these moieties to tailor the inertness or bioreactivity of nanoshells, making them an ideal choice for therapeutic applications and biosensing [219; 220]. Yang et al. used hollow porous nanoshells (HPNShs) of a PtAg bimetallic alloy modified on a GCE to fabricate an ultrasensitive electrochemical biosensor for superoxide anion (O2\({}^{\bullet-}\)), a well-known regulatory mediator in immune and signal processes [221]. The porous surface and the interconnected grains of the nanoshell make it especially conducive to electrochemical sensing. The hollow structure in association with the porous surface promoted greater reaction medium contact. The copious pores integrated with the interconnected backbone assisted the unlimited mass and electron transport during the electrochemical catalysis [222; 223]. The biosensor provided an exceptional response for real time O2\({}^{\bullet-}\) sensing in cellular medium, offering a detection range of 0.8-1080 nM and a detection limit of 0.2 nM. Phan and co-workers used Cushell-Aucore nano particles for the determination of cultural filtrate protein (CFP-10), a _Mycobacterium tuberculosis_ antigen, with the help of a dot-blot immunoassay, which allowed a highly sensitive detection by the naked eye [149]. Prior to growing the Cu nanoshells, gold binding polypeptide antibodies (GBPAb) were immobilised on the AuNPs. The CuNShs induced the appearance of colour intensity in the 0.015-1 ng mL\({}^{-1}\) concentration range and the LOD was 7.6 pg mL\({}^{-1}\). Due to the ease of evaluation using the naked eye or a smart phone camera, the sensor holds great promise for POC testing. Gao et al. used an in situ amplified colorimetric immunosensor based on an extremely efficient peroxidase mimetic system using PtShell-Aucore urchin-like nanohybrids (Ptshell-AucoreNHs) [224]. The urchin-like  
Figure 10: (**a**) Nanocage [217], (**b**) nanoshells [218], (**c**) nanowire arrays. nanoh hybrids could vastly outperform HRP in performance and provided linear responses from 5 to 500 pg mL-1 with an LOD of 2.9 pg mL-1. Nanowires (NW) belong to the class of monodimensional nanoparticles, which also includes nanotubes, nanobelts, and nanorods (Figure 10c). The length of NWs is at least 1000 times their diameter. Semiconducting substances such as Si, InP, and GaN, as well as dielectric materials such as TiO2 and SiO2, can be used to make NWs [2]. Noble metal NWs exhibit thickness dependent LSPR properties. SiO2 NWs find often implementation in FET biosensors, owing to their conductive properties, and hold enormous potential for healthcare biosensing. Signal transduction based on NWs acting as substrates for receptor immobilisation to allow binding with various biomolecules results in sensitive detection, rapid analysis, and a scope for miniaturisation [155].