Practical Aspects of Near-Field Optical Microscopy

Abstract

The study of synaptic transmission has been significantly facilitated by the use of optical techniques to monitor calcium influx and vesicle cycling. However, the optical microscope is limited by diffraction putting a lower limit of 250 nm on spatial resolution. Near-field Scanning Optical Microscopy (NSOM) is a scanning probe technique that utilizes a sub wavelength light source in close proximity to the surface of a sample to generate optical images with a lateral optical resolution below the diffraction limit (about 20–50 nm). In this chapter the NSOM technique is discussed together with its initial application to biological samples. The concept of NSOM predates its more familiar cousins of Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) by six decades. It was first considered theoretically in 1928 by Synge[l] and first demonstrated with microwave radiation in 1972 by Ash and Nicholls [2]. However, due to experimental difficulties it was not until 1984, and the advent of STM, that it was possible to demonstrate the technique using visible light [3].