Cholesterol biosensors prepared by layer-by-layer technique

The analysis of formation, deposition and characterization of cholesterol o xidase (COX) layer-by-layer films were performed. Initially, a layer of pol yanion, poly(styrene sulfonate) (PSS) was adsorbed followed by a layer of p olycation, poly(ethylene imine) (PEI) on each solid substrate from aqueous solutions. The alternating layers were formed by consecutive adsorption of polycations (PEI) and negatively charged proteins (COX) and cholesterol est erase (CE). A strong interaction between protein and polyelectrolyte improv es the stability of the alternating multilayer; however, it can change a na tive protein conformation and impair the protein activity. The PSS/PEI/COX, PSS/PEI/COX/PEI/CE, PSS/PEI/COX-CE/PEI etc. layered structures were prepar ed on the surface of a platinum electrode. ITO coated glass plate, quartz c rystal microbalance, quartz plates, mica and silicon substrates. Optical an d gravimetric measurements based on an ultraviolet-visible absorption spect roscopy and a quartz crystal microbalance revealed that the enzyme multilay ers thus prepared consist of molecular layered of the proteins. The surface morphology of such bilayer films was investigated by using atomic force mi croscopy. The electrochemical redox processes of the enzyme-layered films d eposited either on platinum or ITO coated glass plate were investigated. Th e response current of cholesterol oxidase electrode with concentration of c holesterol was investigated at length. (C) 2001 Elsevier Science B.V. All r ights reserved.