UC Irvine

One of the greatest challenges in global health is to develop inexpensive technologies that are highly sensitive, rapid in readout, and selective for particular agents. Fluorescence is widely used in diagnostics due to its sensitivity and specificity, but an ongoing challenge is to detect and quantify low concentration of target biomolecules and specifically by amplifying the fluorescence signal. Efforts to enhance the fluorescence signal relative to the background have been employed using nanoscale metallic structures and reflective surfaces. These studies have shown that by manipulating the interaction of light with these types of structures, enhancements in the fluorescence signal can be achieved.

Motivated by the need for earlier, better detection of infectious diseases, in this dissertation, commodity shrink wrap film is used as a platform and combined with top-down and bottom-up approaches for two underlying intentions: to create scalable methods for synthesis of tunable structures, and to provide an inexpensive, sensitive fluorescence biosensor. We present a simple approach to pattern metal films onto the shrink wrap film and leverage the stiffness mismatch during the shrinkage to create nano to microscale metallic structures. The use of these metallic structures is demonstrated by depositing fluorescently labeled molecules on top and studying the characteristic properties of the fluorophore's interaction (intensity, emission spectra, and lifetime) with the structures. We demonstrate that our metallic structures can enhance the fluorescence signal relative to a planar surface by more than 1000 fold and show that the fluorescence lifetime is shortened to the point of the detection limit of the system. We also present methods to self-assemble colloidal particles onto the shrink wrap film and etch the particles to various sizes and leverage the shrinkage of the shrink wrap to control the gaps between the etched particles. Finally, we present a manufacturable and scalable method for fabrication of multi-scale wrinkled silica (SiO2) structures on shrink-wrap film for far-field fluorescence signal enhancements in DNA fluorescence microarrays. Our SiO2 structured substrate has an improved detection sensitivity (280 pM) relative to planar glass slide (11 nM) and an improvement of 30-45 times in the signal to noise ratio (SNR). The techniques presented in this dissertation to make these low-cost structures are simple but yield significant enhancements in the fluorescence signal. Development of such tools open up the potential to bring a rapid, portable, sensitive, diagnostic device that could potentially aid in detection of diseases at an earlier stage of infection.