Exploitation of orientation of liquid crystals 5CB and DSCG near surfaces to detect low protein concentration

We report the alignment of 4-cyano-4-pentylbiphenyl (5CB), a thermotropic liquid crystal (LC), and disodium chromo glycate (DSCG), a lyotropic LC, on the hydrophobic head group containing dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DMOAP) and hydrophilic amine head group. Based on the texture observed using a polarised microscope for modified surfaces, we propose the alignment of the LCs on the modified surfaces. It is further supported by Fourier transform infra-red spectroscopy (FTIR) data of the corresponding system. Next, the texture under a polarised microscope for the LCs on protein bovine serum albumin adsorbed over the amine and DMOAP surfaces was observed. The difference in texture of LCs over the proteins depends on its concentration in solution. The difference is due to the amount of adsorbed proteins present on the surface. Above a critical amount of protein at the surface, the LCs show homeotropic arrangement.