Single molecule analysis of DNA immobilized on microspheres

The formation and analysis of single molecules of fluorescently labeled DNA immobilized on polystyrene microspheres is described. Analysis by confocal fluorescence microscopy revealed single-step photobleaching, characteristi c of a single fluorophore. Microspheres provide a means of locating single molecules by bright-field microscopy, prior to single-molecule detection. T his allows the interrogation of single molecules without suffering the limi tations of premature photobleaching. Statistical analysis of fluorescence i ntensities for >100 microspheres suggests attachment of DNA to micropsheres to be consistent with Poisson statistics.