Using Reflectometric Interference Spectroscopy to Real-Time Monitor Amphiphile-Induced Orientational Responses of Liquid-Crystal-Loaded Silica Colloidal Crystal Films.

An approach to optical transduction and amplification of amphiphile-triggered orientational responses of liquid crystals (LCs) based on the interference effect was developed. The sensitive substrate was obtained by lading 4'-pentyl-4-cyanobiphenyl (5CB) into three-dimensionally ordered silica colloidal crystal (SCC) films. Changes in the optical thickness (ΔOT) of the substrates, which are inverted by their Fabry-Perot fringes, depend on the changes of the refractive index caused by the differences in the orientations of LCs. The orientation changes of LCs loading into SCC films have the effect of amplifying signals. These are based on the interactions between surfactants (alkyl trimethylammonium halides (CnTABs, n = 8, 10, 12, 14, and 16) and sodium lauryl sulfonate (SLS)) and LCs, which induce a particular orientation of the LCs molecules. In this flowing system, the reversibility of the signal response for the adsorption of amphiphile was related to the length of the surfactant chain and its critical micelle concentration (CMC). A new method capable of real-time sensing adsorbate-triggered anchoring transitions based on LC-infiltrated SCC films was accomplished. These results provide basics and principles for online, label-free, and real-time analysis of molecules and their interactions in a flowing environment based on the interference effect.