Bioinspired Nanostructures for Biomedical Applications

Nature boasts a myriad examples of coloration achieved purely through the physical interaction of light with nano-scale features also known as biophotonic nanostructures. From reptiles to insects, birds to flora, structural coloration has been achieved through a variety of fascinating nano-architectures that leverage different physics. Beyond structural coloration, these nanostructures are often truly multifunctional. For instance, biophotonic nanostructures can also serve as self-cleaning and bactericidal surfaces, gas and thermal sensors, waveguides and beam splitters. With the growing need for robust and compact biomedical devices, the requirement to embed multiple functionalities towards sensing, monitoring, diagnostics and therapeutics within a diminutive device footprint becomes crucial. In this regard, inspiration from the multifunctionality of biophotonic nanostructures can prove to be greatly beneficial for medical applications. Consequently, this work attempts to showcase various examples of the utilization of nanostructures inspired from biophotonic nanostructures for biomedical applications under various overlapping themes such as ophthalmic sensors, bioinspired optics and plasmonic biosensing. This thesis is summarized in two parts. The first part (Chapters 2--4) introduces a proof-of-concept optical intraocular pressure (IOP) sensor implant and various challenges faced during its in vivo implementation. In Chapter 3, nanostructures inspired by light-trapping epidermal micro-/nanostructures on flower petals are proposed and embedded onto the sensor platform to improve its in vivo optical signal-to-noise ratio and biocompatibility. Chapter 4 covers nanostructures inspired by biophotonic nanostructures on longtail glasswing butterfly wings that improve the in vivo angle of acceptance and biocompatibility of the sensor. The second part (Chapters 5 and 6) presents the use of bioinspired nanostructures in plasmonic biosensors. Chapter 5 discusses an on-chip platform consisting of bioinspired plasmonic nanostructures to detect various nucleic acid sequences of relevance in the pathogenesis of HIV-1 via plasmon-enhanced fluorescence. Chapter 6 describes the employment of bioinspired quasi-ordered nanostructuring on flexible substrates for broadband surface-enhanced Raman spectroscopy (SERS). Here, SERS-based biosensing enabled by quasi-ordering is used to detect uric acid -- a biomarker of various pathologies in human tears.