The role of ligand-receptor interactions in visual detection of HepG2 cells using a liquid crystal microdroplet-based biosensor

Liquid crystal (LC) microdroplets have been prepared for visual detection of HepG2 cells using 4-cyano-4′-pentyl biphenyl molecules in the presence of sodium dodecyl sulfate as a mediator and β-galactose-conjugated poly(styrene-b-acrylic acid) block copolymer (PS-b-PA-G) as a modifier of LC-water interfaces. To clarify the effect of β-galactose-containing ligands on the orientational transitions of LC microdroplets, maltotriose as a ligand simulant was conjugated to poly(styrene-b-acrylic acid) and used as a LC modifier. The interaction of HepG2 cells with the β-galactose-conjugated block copolymer was effective in causing orientational transitions, from radial to bipolar, in LC microdroplets, whereas interactions of HepG2 cells with maltotriose-conjugated block copolymers were ineffective in inducing orientational transitions in LC microdroplets. To confirm the necessity of the PS segment of the block copolymer for transmitting the ligand-receptor interaction forces from the interface to the core of the LC microdroplets, β-galactose-conjugated block copolymers (PS-b-PA-G) and homopolymers (PVLA) were synthesized and used to prepare LC microdroplets. The LC microdroplets containing a β-galactose-conjugated homopolymer did not show orientational transitions upon contact with HepG2 cells. However, LC microdroplets containing a β-galactose-conjugated block copolymer showed orientational transitions from radial to bipolar, indicating that the polystyrene segment in the amphiphilic block copolymer is essential for the effective transmission of ligand-receptor interactions to the core of LC microdroplets. β-Galactose anchored LC microdroplets were able to detect 1.0 ± 0.1 HepG2 cells per μm² of the test cell and had shown significantly high reproducibility (p < 0.05, n = 3). The configurational transition in LC microdroplets that was dependent on ligand-receptor interactions was used to develop a LC microdroplet-based biosensor for the detection of HepG2 cells in biological fluids.