Two-channel sequential single molecule measurement

Experimental results are given which demonstrate the sequential detection of single molecules with a measurement efficiency of near unity. IR140 dye molecules are detected in sequential probe volumes within a flowing stream through a 9 mu m i.d. capillary. The measurement of single molecules was confirmed by means of autocorrelation, photobleaching, visual observation, and crosscorrelation analysis, The number of single molecules photobleached prior to being measured in the second probe region was in excellent agreement with the bulk studies described by a photodestruction curve. A crosscorrelation peak with a temporal delay corresponding to the interprobe volume transit time and a width in agreement-with parabolic now give a clear indication of sequential detection. The near unity measurement efficiencies for both channels indicates the great potential for rapid quantitative analysis of dilute solutions.