Detection of catalase activity with aldehyde-doped liquid crystals confined in microcapillaries

In this study, a simple, rapid, and label-free sensor was developed for detecting the enzymatic activity of catalase (CAT) with liquid crystals (LCs) confined in microcapillaries. Inside a microcapillary functionalized with n-octyltrichlorosilane, aldehyde-doped LCs anchored radially so that a pattern of straight lines was observed under a polarized optical microscope (POM). However, once hydrogen peroxide (HP) oxidized the aldehyde into carboxylic acid, which has surface activity, the orientation of the LCs at the interface changed, resulting in a distinct pattern change, from straight to crossed. In this system, the enzymatic activity of CAT could be detected as it inhibits the oxidation by decomposing HP; as a result, the pattern changed back to the straight one. From the orientational and optical shift, the enzymatic activity of CAT was detected up to a concentration of 0.8 fM under mild experimental conditions and 8 aM at pH 9.0. This result suggests the need for further study of microcapillary systems to develop simple and sensitive sensors for biochemical interactions.