Tunable one-dimensional photonic crystals based on metal-organic framework, silica and titania nanoparticles as sensing platforms

“Smart”, stimuli-responsive photonic crystals (PCs) for label-free biological, chemical and physical sensing applications have recently garnered significant attention from various scientific communities, such as photonics, materials chemistry and biotechnology and represent a fast growing research field. Particular interest is attracted by conceptually simple, yet versatile one-dimensional PCs, christened Bragg stacks (BSs), which are interference-based optical multilayer structures consisting of a periodic stack of layers of two different materials featuring high and low refractive indices, respectively. The sensing approach is based on the utilization of such PCs as tunable optical filters capable of dynamically changing their refractive properties when in contact with an analyte of interest, or when exposed to external stimuli such as temperature, electric and magnetic fields, etc. Due to the periodicity of the dielectric lattice of the multilayer structure, which creates a periodic potential for photons in one dimension, the optical spectra of BSs exhibit a forbidden wavelength range for photons with particular energies, called the photonic stop band. The position of the stop band can be modulated by varying the optical thickness (the product of refractive index (RI) and physical thickness) of the layers in response to an external stimulus. In this report we propose photonic crystals designed in particular for vapor and temperature sensing based on the deposition of metal-organic framework/titania and silica/titania multilayers, respectively.