Multimodal spectrometric and dielectric biosensing with an ionic-surfactant-doped liquid crystal

The conventional principle of liquid-crystal (LC)-based biosensing stems from change in LC orientation caused by biomolecule-induced disruption of otherwise ordered LC alignment so that the resulting textural change or light leakage can be detected under a polarizing optical microscope. In this study, a cationic surfactant, cetyltrimethylammonium bromide (CTAB) was doped into LCs to take advantage of the complex formed between the cation and the analyte; i.e., bovine serum albumin (BSA), in biodetection. The optical response of immobilized BSA becomes discernable by applying DC voltage across the LC cell thickness to transduce the disturbance in LC alignment into detectable optical signal and enable quantitative bioassays through transmission spectrometry. On the other hand, dielectric analysis readily permits excellent BSA quantitation without the need of DC voltage, ensuring a limit of detection of 2.7 × 10^–11 g/ml of BSA at null bias voltage, which greatly outperforms textural brightness analysis leading to a limit of detection of 2.9 × 10^–9 g/ml and transmission spectrometric analysis with a limit of detection of 6.6 × 10^–10 g/ml at a bias voltage of 2.3 V. The LC-based protein assay platform disclosed in this work opens a new doorway toward label-free biosensing for multimode quantification.