Inverse Opal Photonic Crystals as Diagnostic Sensors

Inverse opals are self-assembled 3D photonic crystals with a unique potential for colorimetric diagnostic sensing of both soluble biomarkers and viral particles. Changes to their structural color due to the selective wetting of pores and subsequent change in the effective refractive index of the inverse opal can be used to easily visually distinguish between fluids with different physical properties, which can be indicative of disease states, or to determine the presence of bound particles. As the wetting point of the pores is determined by pore geometry and the contact angle formed with the testing fluid, these structures are highly customizable for use in different diagnostic systems. The colorimetric differentiation of fluids with nanomolar to micromolar concentrations of surfactants including bile salts is made possible by patterning the surface chemistry of an inverse opal with silanes of different hydrophobicities. Detection of viruses with an optical microscope has been enabled by observing the change in the wetting of a test solution into the structure due to the geometric change induced by the binding of a virus to the pore wall. By understanding how pore geometry and surface chemistry contribute to the interactions between inverse opals and fluids, we can more effectively utilize these structured materials for diagnostic sensing.