Photonic Biosensors Based on Smart Solid-State Cholesteric Liquid Crystals

Solid-state cholesteric liquid crystal (CLCsolid) is one-dimensional photonic material, reflects only one-handed circularly polarized light depending on the handedness of its helical pitch. The helical structure has the spatial modulation of refractive index that creates energy band structure for photons, which either allows or stops the propagation of light of certain wavelength ranges. The wavelength of the reflected color is directly related to the length of helical pitch of the corresponding CLCsolid. Therefore, these photonic materials can be developed to give an optical response to external stimuli such as pH, mechanical force, temperature, and humidity which can alter the helical pitch of CLCsolid. This dissertation describes the research conducted to develop stimuli responsive smart CLCsolid. The pH responsive smart CLCsolid was developed through an interpenetrating polymer network (IPN) of the weak polyelectrolytes in CLCsolid. The volume of this intertwined polyelectrolyte hydrogel is expanded on pH change which increases the helical pitch of the CLCsolid. Thus, the reflected color of the smart CLCsolid shifts to red. In this research, we used smart CLCsolid as an optical biosensor for the detection of biomolecules such as glucose and urea.