Electrohydrodynamic mechanisms of dynamic scattering in dual-frequency liquid crystals for label-free biosensing

Chia-Tung Chang^1*, Mon-Juan Lee², Wei Lee³

¹Institute of Lighting and Energy Photonics, College of Photonics, National Yang Ming Chiao Tung University, Tainan, Taiwan
²Department of Biomedical Science and Technology, College of Medicine, National Sun Yat-sen University, Kaohsiung, Taiwan
³Institute of Imaging and Biomedical Photonic, National Yang Ming Chiao Tung University, Tainan, Taiwan

* Presenter:Chia-Tung Chang, email:gaven097223@gmail.com

This study investigates a label-free biosensing mechanism based on the electrohydrodynamic (EHD) instability of a dual-frequency liquid crystal (DFLC) operating in the dynamic scattering mode (DSM). By driving the DFLC near its crossover frequency where dielectric torque is minimized, ion-driven convective flows dominate, producing a dynamic scattering state highly responsive to interfacial perturbations. Surface-immobilized bovine serum albumin (BSA) systematically alters anchoring strength and ionic conductivity at the LC–substrate interface, effectively lowering the EHD instability threshold voltage. As a result, under a fixed driving voltage, samples with higher protein concentrations exhibit stronger scattering intensity, quantitatively analyzed by haze measurement. The sensing response shows excellent linearity over a wide concentration range with a detection limit below 1 ng·mL–1. These results highlight the strong coupling between dielectric relaxation, ionic motion, and surface anchoring in DFLCs, thereby establishing the DSM-driven EHD mechanism as a robust physical framework for label-free optical biosensing.

Keywords: LC-based biosensor, Haze measurement, Dynamic scattering mode, Electrohydrodynamic instability, Label-free detection