Picture: Images from a FRAP experiment with FITC molecules diffusing in a solution of Polyethylene glycol of average weight 400 g/mol and water at times 0.34 s, 3.40 s and 6.46 s after bleaching
The FRAP (fluorescence recovery after photo bleaching) technique is an efficient and versatile method for estimating diffusion coefficients. The figure shows images obtained with a confocal microscope at three times after bleaching with a high energy laser in a cylindric beam orthogonal to the image plane. It is clearly visible how the fluorescent diffusing molecules are invading the area heavily bleached in the leftmost image. By use of maximum likelihood techniques applied to sequences of images we are presently refining available computational techniques to acquire higher accuracy. The methods developed will also be used to design new types of experiments that will allow study of transient structures.