LIGHT-MICROSCOPY OF THE STRUCTURE OF A GEL

The fibrous network of those agarose gels typically used for electroph oresis is too fine to observe by light microscopy. In the present stud y, light microscopy, apparently for the first time, reveals the fibrou s network of an agarose gel that has a micrometer-scale fibrous networ k. The agarose used is a derivatized, irradiated agarose previously sh own by electron microscopy to have the following characteristic: When a 1.5% gel is cast at 30 degrees C, but not at 10 degrees C, fibrous b undles of agarose chains partition to form wider fibers that, in turn, form a network that has micrometer-sized and larger pores. When obser ved by phase-contrast light microscopy, gels cast at 30 degrees C have a clearly defined fibrous network not present for gels cast at 0 degr ees C. The temperature-dependence of the network observed by light mic roscopy indicates that this network is the same as the micrometer-scal e network observed by electron microscopy. For the network observed by light microscopy, the mean chord length varies inversely with the aga rose concentration. The least concentrated gel observed had a concentr ation of 0.3%. Slight pressure on a 0.4% gel caused microfracture of t he gel, thereby producing pores of a dimension between 5 and 50 mu m. These pores, freely permeable to latex spheres, will be useful for det ermining the hydrodynamic damping of intrapore, single-particle motion by gel fibers. (C) 1994 Academic Press, Inc.