Electric-field-assisted signal amplification for label-free liquid-crystal-based detection of biomolecules.

The fundamental principle of liquid-crystal (LC)-based biosensing is the sensitive response of LC orientation to external stimuli. Biomolecules such as proteins or DNAs immobilized on the glass substrate of a LC cell are detected through disrupting the LC alignment and, in turn, altering the birefringence, resulting in changes in the optical texture that can be readily observed under a polarizing optical microscope. With an additional weak electric field across a sandwiched LC cell, we demonstrate in this study a novel label-free biodetection technique with amplified signal and improved detection limit. By applying the binarization analysis as the quantitative approach, the increase in the light leakage area in the optical texture of LCs with increasing amount of biomolecules can be quantitated with a bright-area-ratio (BAR)-versus-concentration curve. The reported biosensing technique exploits both the optical and electrical properties of LCs and is potentially applicable to other LC-based rapid screening and bioassays.