Immobilization of oligoglycines on aldehyde-decorated surfaces and its influence on the orientations of liquid crystals

This paper reports an investigation of the immobilization of glycine (Gly), glycyl-glycine (Gly-Gly), and glycyl-glycyl-glycine (Gly-Gly-Gly) on silica substrates (colloidal silica, silicon wafer, and glass slides) decorated with aldehyde functional groups. It is found that the density of Gly or oligoglycines immobilized on the surface can be greatly enhanced by using higher ionic strength (∼1 M) and a reaction temperature of 50 °C. High ionic strength was used to screen the electrostatic repulsion caused by the negatively charged carboxylate groups of Gly or oligoglycines, while higher temperature was needed to increase the reaction rates. It is also found that when a thin layer of nematic liquid crystal 4-pentyl-4′-cyano-biphenyl (5CB) was supported on a Gly or oligoglycine-decorated surface, the orientation of 5CB changed from planar to homeotropic (perpendicular to the surface) over a period of 24 h. Furthermore, the switching time decreased when the surface density of oligoglycines was increased, and when the length of oligoglycines was increased by one or two Gly residues. The kinetic information provides a means to distinguish Gly, Gly-Gly, and Gly-Gly-Gly that only differ by a single Gly without using fluorescence or radioactive labeling. This method also has good spatial resolution over a large area that permits the detection of multiple oligoglycines patterned on the same surface.