AFM, SECM and QCM as useful analytical tools in the characterization of enzyme-based bioanalytical platforms

One of the key issues to develop biosensing platforms concerns the processes involved in enzyme immobilization on surfaces. The understanding of their fundamentals is crucial to obtain stable and catalytically active protein layers for developing successful biosensing devices. In this respect, the advent and development of new characterization techniques, in particular at the submicron level, has allowed the study of these processes with high resolution, which has opened new routes to improve, and eventually control, enzyme immobilization on electrode surfaces. This review focuses on the application of Atomic Force Microscopy (AFM), Scanning Electrochemical Microscopy (SECM) and Quartz Crystal Microbalance (QCM) techniques in the characterization of the successive immobilization steps involved in the development of bioanalytical platforms. A common advantage of these techniques is their ability to provide important information without damaging the immobilized biological sample due to the possibility of performing measurements under physiological conditions close to the native environment of the specimens. A particular emphasis is placed on the application of these techniques to the characterization of the immobilization of enzymes on different modified and unmodified surfaces as well as on the study of protein interactions, which is a more recent and less current application.