An integrated liquid crystal sensing device assisted by the surfactant-embedded smart hydrogel

The abnormal levels of trypsin in biological fluids can cause some acute illnesses, such as acute pancreatitis, cystic fibrosis and malnutrition. In this paper, we report the development of an integrated liquid crystal (LC) sensing device for simple, rapid and sensitive detection of trypsin assisted by the surfactant-embedded smart hydrogel. The gelatin hydrogel mixed with CTAB is added into the side channel of the LC sensing device. In the presence of trypsin, the gelatin hydrogel is decomposed, which triggers instant release of CTAB into the aqueous solution. The CTAB molecules are then captured by the LCs and form CTAB monolayers at the aqueous/LC interface, which leads to change of the LC images from the bright to the dark appearance under the crossed polarizers. The integrated LC sensing device has a remarkable detection limit of 3.4 × 10 −5  mg/mL. It is successfully employed to single-step detection of trypsin in human serum within 30 min. The integrated LC sensing device with use of the surfactant-embedded hydrogel takes advantages of single-step detection, high portability, remarkable sensitivity and fast response time, which provides a new perspective to facilitate development of user-friendly LC-based sensors.