Using liquid crystals for the label-free detection of catalase at aqueous-LC interfaces.

In this study, we developed a simple label-free method for the detection of catalase (CAT) using liquid crystals (LCs). The optical appearance of LCs changed from bright to dark when hydrogen peroxide was in contact with the dodecanal-doped nematic LC, 4-cyano-4'-pentylbiphenyl (5CB). Since hydrogen peroxide can oxidize aldehyde into carboxylic acid, an orientational transition of the LC from the planar to homeotropic state was induced by the self-assembled carboxylate monolayer formed at the aqueous/LC interface. The optical response of LCs exhibited a higher sensitivity to the presence of hydrogen peroxide in an alkaline solution. A new type of LC-based sensor was developed to monitor the presence of CAT in the aqueous phase. Due to the enzymatically catalytic hydrolysis of hydrogen peroxide, the bright-to-dark shift in the optical signal did not take place in the aqueous mixture of hydrogen peroxide and catalase. In contrast, the optical response changed from bright to dark when the mixture in the optical cell was replaced with an aqueous solution of hydrogen peroxide. Considering the optical response of LCs related to the absence and presence of hydrogen peroxide, the aldehyde-doped 5CB might have potential utility in real-time recognition and detection of chemical and biological events associated with hydrogen peroxide.