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Reduction of luminescent background in ultrasensitive fluorescence detection by photobleaching.

In luminescence-based ultrasensitive analysis, such as single-molecule detection by flow cytometry, the luminescence background from impurities present in the solvent or reagents can ultimately determine the detection limits. A simple, versatile method for reducing luminescence background is described. The method is based on photobleaching the reagent stream immediately before it enters the detection flow cell. Dramatic reduction (an order of magnitude or more) of both low-level continuous background and single-molecule fluorescence bursts is demonstrated. Application and enhancements of the technique are discussed.