From Single-Molecule DNA Imaging to Development of a Gene Delivery System

Abstract

The fundamental properties of single DNA molecules clarified by single-molecule DNA imaging using fluorescence microscopy and related applications are briefly introduced in this chapter. Firstly, the basis of fluorescence video microscopy for single-molecule DNA imaging is discussed. The physical quantities determined from image analyses are in accordance with those obtained by conventional methods that measure the ensemble averages of physical properties, although the dynamic behavior of DNA molecules observed in fluorescence video microscopy seems to be somewhat different from that found by conventional characterization. DNA solution properties as a basis of polymer physics are also described in relation to optical tweezers. An essential concept of polymer physics, the “reptation model,” is proven by single-molecule imaging and provides useful information about the molecular mechanics of DNA gel electrophoresis, which is a widely used tool in biology and biochemistry. A mechanism of DNA condensation that is closely related to the traditional problem in polymer physics known as the “coil-globule transition” is also clarified using single-molecule DNA imaging. This transition has recently attracted considerable attention as an elemental technology for gene therapy. A promising nonviral gene delivery system is also introduced along with the newly developed advanced imaging technique intravital real-time confocal laser scanning microscopy.