Distribution of single molecules in polymer thin films

Distribution of fluorescent dye molecules in polymer thin (similar to 100nm ) films was investigated using far-field single-molecule video microscopy, by varying concentrations of dye molecules mixed in the polymer. Histograms of fluorescence photocounts of individual fluorescent spots showed wide di stribution, varying in the number of fluorescent spots composed of one, two , three or group of molecules. The number of the molecules present in the f luorescent spots was also ascertained by fluorescence photobleaching experi ments. Photocounts associated with maxima of the histograms were found to b e independent of the concentrations; however, the number of occurrences ass ociated with mol e th;in one molecule decreased with decreasing concentrati on. By reducing concentration as well as by mixing dye molecules into a pol ymer solution, fluorescent spots grouping more than one molecule were separ ated considerably into fluorescent spots including a single-molecule. (C) 2 001 Elsevier Science B.V. All rights reserved.