Fabrication And Characterization Of Novel Biosensors Based On Photonic Crystal Beads

Photonic crystals (PCs) are nanostructures that are composed of two or more periodically ordered materials of different refractive indices. Refractive indices in a PC vary periodically on a scale of the order of the wavelength of UV, visible and infrared radiations. The propagation of electromagnetic waves through PCs is either allowed or forbidden in the same manner as the periodic potential for electrons through atomic crystal lattices, giving rise to their characteristic photonic bandgap and photonic localization properties. Responsive photonic crystals are materials with photonic bandgap properties that can be tuned by external stimuli. Being a combination of responsive materials and photonic crystals, responsive photonic crystalline materials can change their volume or phase in accordance with certain responsive mechanisms, resulting in changes of their photonic bandgap properties in the UV, visible and infrared regions of the electromagnetic spectrum.Recently, a lot of attentions have been paid to the application of responsive photonic crystals in various fields. In this dissertation, the fabrication of photonic crystal beads from stimuli-responsive microspheres, and their applications in bio-imaging are explored.Chapter1introduces the theories behind the photonic bandgap properties of PCs and current progresses in the related fields of research. Various novel applications of PCs are also introduced. A brief review on in vivo imaging is also included.Chapter2reports a facile approach for the assembly of PC beads. These beads were constructed from a series of specially prepared monodispersed poly(styrene-co-acrylic acid)(PS-co-PAA) microspheres,"hairy" PS-co-PAA microspheres and core-shell hydrogel microspheres with PS-co-PAA cores and poly(acrylic acid-co-N-isopropylacrylamide)(PAA-co-PNIPAM) hydrogel shells. The composition of the core-shell hydrogel microspheres were fine-tuned with the use of various copolymerization monomers so as to produce PC beads with desired photonic properties for biosensing and in vivo bio-imaging.Chapter3reports an application of pH-responsive photonic band-gap materials in in vivo imaging on a test organism-Japanese medaka, Oryzia latipes. The PC beads were assembled from monodispersed core-shell hydrogel microspheres with PS-co-PAA cores and cross-linked PAA-co-PNIPAM shells. These PC beads were found to possess enough structural integrity for in vivo imaging under conditions as harsh as the peristaltic movement of the gut. They have also shown no apparent toxicity to the test organism. The volume phase transition of the acrylic acid-based hydrogel of the core-shell particles compiling the photonic beads has given rise to the pH responsive properties of the PC beads.Chapter4reports the bio-imaging investigation of the morphology and ionic strength regimes of the gastrointestinal tract of freshwater and marine medaka using photonic crystal beads. The special designed and fabricated monodispersed core-shell hydrogel microspheres possessed a (PS-co-PAA) core and a poly(hydroxyethyl methacrylate-co-sodium p-styrene sulfonate)(PHEMA-co-PSS) shell. Photonic properties of the resulting PC beads assembled from the core-shell hydrogel microspheres were found to be dependent on the media ionic strength as the volume phase transition of the hydrogel was able to cause changes in the crystalline colloidal array lattice spacing. These PC beads were able to respond to different concentration of sodium chloride (ranged from0.5mM to500mM).Chapter5reports overall conclusions and recommendations for further investigations.