Inverse opal sensors

Shin J, Braun PV, Lee W (2010) Fast response photonic crystal pH sensor based on templated photo-polymerized hydrogel inverse opal. Sensor Actuat B Chem 150 183... 

Scheme 10.5 Principles of various sensing methods based on light interference or diffraction (a and b) PCCA sensors (c and d) Fabry-Perot sensors (e) holographic sensor (f) inverse opal sensor (g) diffraction grating sensor.

Inverse Opal Sensors. Colloidal crystals are ordered crystalline structure obtained via the self-assembly of monodispersed colloidal particles. Dried colloidal crystals can be used to template the polymerization of infiltrated monomer precursors. After polymerization, the colloidal template is removed by chemical etching, yielding a bicontinuous polymer/solvent mesostructure, i.e., inverse opal. Because of its periodically ordered structure inherited from the colloidal crystal template, inverse opal also shows structural color as a result of light diffraction. This property has also been used to design optical glucose sensors (Scheme 10.5f). 

A plasmonic response of the gold/silica composite inverse opals was observed (Fig. 3b), which showed a pronounced spectral change upon the variation of the surrounding dielectric medium by addition of glycerol to the water phase. This property suggests an application of the hierarchically structured replica in the field of optical sensors. 

Lee YJ, Braun PV (2003) Tunable inverse opal hydrogel pH sensors. Adv Mater 15 563... 

As naturally abundant and low-cost semiconductor, NiO is widely used in electrochromic windows [20], batteries [21], supercapacitors [22], and sensors [23], While all these applications benefit from an interconnected, three-dimensional NiO nanostructure that combines a high specific surface area with a good electric conductivity, the performance enhancement becomes vividly evident as an increased coloration contrast and improved switching behavior when applied in electrochromic devices. NiO nanomaterials recently employed in electrochromic studies include nanocomposites [24], inverse opals [25], macroporous [26] and mesoporous films [27-29],... 

Another nice example of nanostructuring an MIP layer is the work published by Wu et al. [138, 139] who developed a label-free optical sensor based on molecularly imprinted photonic polymers. Photonic crystals were prepared by self-assembly of silica nanospheres. The space between the spheres was then filled with MIP precursor solution. After polymerization, the silica was dissolved, leaving an MIP in the form of a 3D-ordered interconnected macroporous inverse polymer opal (Fig. 15). The authors were able to detect traces of the herbicide atrazine at low concentrations in aqueous solution [139]. Analyte adsorption into the binding sites resulted in a change in Bragg diffraction of the polymer characterized by a color modification (Fig. 15). 

---