Inverse Opals as Diagnostic Sensors

As porous 3D photonic crystals, inverse opals have a unique potential for colorimetric diagnostic sensing. Changes in their structural color due to wetting of the pores and subsequent change in effective refractive index can be used to easily and visually distinguish between fluids with different physical properties, including surface tension and chirality, which can be indicative of disease states. As the wetting point of the pores are determined by pore geometry and the contact angle formed with the testing fluid, these structures are highly customizable for use in different diagnostic systems. Patterning the surface chemistry of an inverse opal with silanes of different hydrophobicities has enabled the differentiation of fluids with nanomolar to micromolar concentrations of surfactants including bile salts. By functionalizing the surface of an inverse opal with chiral molecules, we can additionally use these structures to visualize the differences between contact angles of chiral liquids on homochiral and heterochiral surfaces to detect fluid chirality, which is important both in drug development and can be a biomarker for disease.