TRANSMISSION AND CONFOCAL FLUORESCENCE MICROSCOPY AND TIME-RESOLVED FLUORESCENCE SPECTROSCOPY COMBINED WITH A LASER TRAP - INVESTIGATION OFOPTICALLY TRAPPED BLOCK-COPOLYMER MICELLES

Optical trapping was combined with transmission microscopy (TM), confo cal and nonconfocal fluorescence scanning microscopy (CFSM and FSM, re spectively), and confocal and nonconfocal time-resolved fluorescence s pectroscopy (CTRFS and TRFS, respectively) to study latex particles an d block copolymer micelles. Dye-labeled latex particles of various siz e, in polymer composite films as well as optically trapped in solution , were studied with CFSM to characterize the limits of the setup. CFSM revealed that the resolution in the x- and y-directions was near the theoretical limit, i.e., 200-250 am. CTRFS on the labeled latex partic les revealed that the decay time of the label was not influenced by th e polymer matrix nor the optical trap. Poly(tert-butylstyrene-block-so dium methacrylate) micelles (diameter approximately 30-40 nm) in deute rated aqueous solutions could be optically trapped, this region of hig h copolymer micelle concentration being referred to as a trapped clust er. In the transmission images, trapped clusters of 1.5-2 mu m diamete r were detected. Fluorescence images were obtained using perylene as a fluorophore that is specifically dissolved within the block copolymer micelles. The size of the trapped cluster, estimated from TM and FSM images, increases with increasing irradiation time and power, respecti vely. In the TM images, the trapped cluster appears as a dark spot (lo w transmission) with a bright (high-transmission) corona-like ring aro und it. The appearance of the corona is explained as a light deflectio n phenomenon; i.e., the trapped cluster acts as lens due to a lateral refractive index gradient. When the corona is taken into account when the diameter of the trapped clusters is calculated, a very good agreem ent is found between TM and FSM. Long irradiation times lead to the fo rmation of large trapped clusters, which are stable for about 10 s, wi th diameters of several hundred nanometers, while, for short irradiati on times, the trapped cluster is smaller and disappears within a time less than 1 s. With CFSM it could be shown that the trapped particle h as a spot size of approximately 1.7 mu m in the region of the IR laser focus, while the diameter extends up to 5 mu m without using the conf ocal imaging capability. The reason for this is that the conditions fo r optical trapping are fulfilled not only in but also above and below the focal region. Due to the high numerical aperture, a dumbbell-like shape of the trapped cluster results.