Design of holographic gas sensor using liquid crystallinity

Abstract

The quick and precise detection of hazardous compounds is important in a variety of fields. If the visual reporting is integrated with the detection, there could be a profound impact on practical applications. In this work, we present a new class of compact sensor platform by combining a stimuli-responsive liquid crystals (LCs) and holographic metasurface (MS) as shown in Figure 1 [1]. Specifically, the metasurface composed of nano structures with sub-wavelength scale was programmed to display two holographic images (smile face for safety signal and exclamation mark for alarm signal) upon the transmission of left- (LCP) and right-circularly polarized light (RCP), respectively. The metasurface was integrated with the LC layer that was designed to transform LCP to RCP in the presence of a target gas by leveraging stimuli-responsiveness and optically anisotropic nature of LCs. Consequently, we demonstrated that the LC-MS system to autonomously sense a target gas (e.g, IPA, methanol, chloroform) and instantaneous report it via the holographic alarm. For instance, the proposed LC-MS gas sensor could detect the ultra-low concentration of IPA gas from a marker pen. Moreover, for their wide applicability, we demonstrate the LC-MS sensors to be selectively responsive to various stimulus (e.g. electrical field, heat, pressure) and to be attachable to flat, curved, and flexible surfaces (e.g., safety goggles) via a one-step nanocasting process [1, 2].