Visualization of cholylglycine hydrolase activities through nickel nanoparticle-assisted liquid crystal cells

Cholylglycine (CG) is an extremely important biomarker used to diagnose liver abnormalities. Herein, we report a novel nickel nanoparticle (NiNP)-assisted liquid crystal (LC) cell system that can be used to visualize the enzymatic activities between cholylglycine hydrolase (CGH) and CG. When doped with trace amounts of NiNPs, the nematic LC, 4-cyano-4′-pentylbiphenyl (5CB), exhibited a uniform homeotropic alignment that provided dark optical outputs under a polarizing optical microscope (POM), at the designed LC sensing cells. These cells were sandwiched between a pretreated gold surface and an indium tin oxide (ITO) glass surface. In this system, the LC molecules were disordered, producing bright optical signals when CG was introduced to the binding CGH immobilized gold surface. We determined the CG detection limit in the “10 pM” level, and quantitatively defined a working range of 0.1 nM to 1 μM. The mechanism of the topographical changes on the reacted surface that led to these results was also verified by atomic force microscopy (AFM). This innovative technique, with its simplified path, shows great advances when compared to existing commercially available enzymatic-based bioassays, and offers an easy-to-use principal allowing the fabrication of practical LC-based sensors for CG detection.