Simultaneous Topography and Recognition Imaging

Atomic force microscopy (AFM) has developed into a key technique for the investigation of biological samples. In contrast to other microscopy methods, high lateral resolution down to the nanometer scale and measurements under physiological conditions are possible. Additionally, the piconewton force sensitivity allows accurate data collection for single-molecule interactions. This chapter describes the combination of high-resolution imaging and single-molecule interaction measurements. In the so-called topography and recognition imaging (TREC) mode, the scanning AFM tip is upgraded into a molecular sensor by anchoring a ligand to the tip. Enhanced electronics, including a recently developed feedback loop, allow measurement of the sample topography while simultaneously mapping ligand-binding sites. This results in topography images recorded alongside with recognition images, thereby allowing accurate allocation of the binding sites with a lateral resolution of one to a few nanometers. TREC has been successfully used for recognition imaging on isolated proteins, native and artificial membranes, and cells.