“TIR Microscopy to Watch DNA Hybridization”
Characterizing the diffusion of DNA-grafted colloidal particles interacting via hybridization with a DNA-coated substrate may help our understanding of biological processes involving cell membranes, such as multivalent adhesion. To do this, we observe the three-dimensional motion of colloidal particles using a custom-made total internal reflection (TIR) microscope. We measure the position of the particles using scattered light from an evanescent wave. The evanescent wave is the result of total internal reflection of a laser from the coverslip-water interface. Since the intensity of the wave decreases exponentially, the amount of scattered light from the particles is related to their vertical position. We then use a suite of custom-made software routines to calculate the mean squared displacement, pair-interaction potential and kinetics of binding. From this data, we hope to characterize how colloidal particles interact via DNA hybridization with a solid substrate, and ultimately understand something about the key physical determinants of avidity and specificity in multivalent binding.