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. Author manuscript; available in PMC: 2011 Dec 1.
Published in final edited form as: Anal Chem. 2010 Nov 9;82(23):9948–9954. doi: 10.1021/ac102173m

Figure 4.

Figure 4

Detection of droplet streams. (a) Time trace showing the detection of individual passing droplets (each photon spike corresponds to one droplet) using the epi-confocal geometry. Each droplet contains 5 nM of fluorescein. (b) Detection of the same droplet stream as in (a), but with orthogonal-line-confocal excitation. (c) Even at 250 pM concentrations of fluorescein, which corresponded to ~2200 molecules of fluorescein in the 30 μm diameter droplet, the signal-to-noise ratio was excellent. The laser power used in (a) and (b) was 0.75 mW, and in (c) was 7 mW.