NONCLASSICAL DIMENSION-DEPENDENT KINETICS OF A PHOTOBLEACHING REACTION IN A FOCUSED LASER-BEAM PHOTOTRAP

A focused laser beam acts as both a ''phototrap,'' bleaching fluoropho re molecules that diffuse into the beam path, and as a confocal probe, detecting the excited, unbleached fluorophore molecules still present in the trap. With this focused laser beam, we observe anomalous asymp totic rate laws similar to those predicted for a diffusion-controlled elementary trapping reaction A+T-->T in both one and two dimensions. O ne-dimensional diffusion-limited trapping kinetics are observed in cap illaries with 10 mu m diameters, while two-dimensional (2D) diffusion limited trapping kinetics are observed with unstirred samples having a quasi-2D geometry. However, in the presence of stirring, the 2D sampl es exhibit the classical, constant trapping rate.