Structural Color and Odors: Towards a Photonic Crystal Nose Platform

The present thesis describes a novel photonic crystal platform dubbed the photonic nose, a color-based analogue of the human olfactory system. The platform is founded on a one dimensional photonic crystal architecture known as Bragg stacks, which are fabricated using bottom-up self-assembly approaches. Structural and compositional aspects of this novel class of photonic crystals are established that provide them with functionality and utility. Silicon dioxide, titanium dioxide, tin oxide, clays and zeolites are among the materials incorporated into one-dimensional photonic structures. Retention of materials functionality is demonstrated by vapor and liquid sensing experiments. This class of Bragg stacks displays well defined optical properties that have been thoroughly investigated by use of spectroscopic ellipsometry, as we demonstrate in a chapter dedicated to the technique. Utilizing conventional building blocks comprised of nanostructured silicon and titanium dioxide we discuss various aspects of technique pertaining single layered as well as multilayered films. In terms of practical applications these kinds of Bragg stacks show significant potential in areas such as display and sensors that exploit their vibrant and tunable colors. These colors are an important attribute of photonic crystals with bandgaps in the visible range and in this thesis work we present new approaches for characterizing photonic crystal color using well established methods from the field of color imagery. With this knowhow we have been able to assemble a pixilated array of chemically functionalized Bragg stacks in which each pixel responds differently to vapor phase analytes. The combinatorial response of the entire array enables a unique diagnostic fingerprint of a given analyte vapor as determined from color imagery and multivariate statistical methods of analysis. It was possible to discriminate between ethanol, butanol, hexanol, hexane, octane and decane. We also demonstrate the power of the photonic nose platform by distinguishing different bacteria from a photonic nose color analysis of the complex mixture of vapors in the bacteria culture headspace. Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa could be discriminated based on this technique.Ph