Fiber-optic Nano-biosensors and Near-Field Scanning Optical Microscopy for Biological Imaging

In recent decades, the rapid development of nanotechnology has led to the broadening of application in many areas. Among these technologies, near-field optics is the one which can provide sufficient resolution suitable for measurement in molecular level in the biological area. Although current light and electron microscopies can yield images in many scales, they do not fit the measurement in the submicrometer scale, which is important for the study of functional molecular complexes ranging from chromosomes to membrane domains. For electron microscopy, even though it is able to resolve structures of samples down to nanometer scales, the samples must be dry and dead. Traditional light microscopy can be applied to the investigation of molecular complexes in living cells, but as its resolution is limited by the diffraction of light (∼250nm), molecular complex structures cannot be resolved. On the other hand, the near-field scanning optical microscopy (NSOM) allows fluorescence imaging at a resolution of a few tens of nanometers. Also, as a result of the extremely small excitation volume, the background fluorescence is greatly reduced and so single-molecule detection becomes possible. In addition, both topography and fluorescent images can be collected simultaneously. As a result, NSOM provides great advances in biological research. Fiber-optic nano-biosensor (FONBS), which is derived from NSOM, is commonly used to investigate intracellular measurement. Taking the advantages of NSOM as well as biological methods, FONBS opens new horizons in environmental and biological monitoring of chemicals and biomolecules within single cells. In this chapter, the basic concepts and developments of both techniques are discussed. The mechanisms and their application to biological systems are also provided in brief.