Protein detection using aqueous/LC interfaces decorated with a novel poly(N-isopropyl acrylamide) block liquid crystalline polymer

The homeotropic to planar orientational change (H-P change) at the interface between 4-cyano-4́-pentylbiphenyl (5CB) and water in the transmission electron microscopy (TEM) grid cell functionalized by decoration of an amphiphilic block copolymer of PNIPAM-b-LCP (PNIPAM; poly(N-isopropyl acrylamide) and LCP; poly(4-cyanobiphenyl-4-oxyundecylacrylate) was used to detect proteins with variations of pH and temperature in the cell. Several proteins including lysozyme, bovine serum albumin, hemoglobin and chymotrypsinogen were detected at levels of a few μM to hundreds of nM through a homeotropic to planar orientational change (H-P change) of 5CB at above the low critical solution temperature (LCST) of PNIPAM and below the pH of PI of the protein. The H-P change through protein adsorption was reversible by changing the temperature above and below PNIPAM's LCST. This TEM grid cell could also detect the proteins in human urine from a patient with albuminuria with a detection limit as low as 5.88 × 10^-5 wt%.