A single-substrate biosensor with spin-coated liquid crystal film for simple, sensitive and label-free protein detection

A liquid crystal (LC)-based single-substrate biosensor was developed by spin-coating an LC thin film on a dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DMOAP)-dec-orated glass slide. Compared with the conventional sandwiched cell configuration, the simplified procedure for the preparation of an LC film allows the film thickness to be precisely controlled by adjusting the spin rate, thus eliminating personal errors involved in LC cell assembly. The limit of detection (LOD) for bovine serum albumin (BSA) was lowered from 10⁻⁵ g/mL with a 4.2-μm-thick sandwiched cell of the commercial LC E7 to 10⁻⁷ g/mL with a 4.2-μm-thick spin-coated E7 film and further to 10⁻⁸ g/mL by reducing the E7 film thickness to 3.4 μm. Moreover, by exploiting the LC film of the highly birefringent nematic LC HDN in the immunodetection of the cancer biomarker CA125, an LOD comparable to that determined with a sandwiched HDN cell was achieved at 10⁻⁸-g/mL CA125 using a capture antibody concentration an order of magnitude lower than that in the LC cell. Our results suggest that employing spin-coated LC film instead of conventional sandwiched LC cell provides a more reliable, reproducible, and cost-effective single-substrate platform, allow-ing simple fabrication of an LC-based biosensor for sensitive and label-free protein detection and immunoassay.