Laser-Induced Fluorescence Detection of Rhodamine-6G at 6 × 10−15 M

Abstract
We have demonstrated sensitive fluorescence detection of rhodamine-6G in aqueous solutions down to ∼10−15 M with a detection limit of 6 × 10−15 M. The working curve was observed to be linear over four orders of magnitude and could be extended to higher concentrations. Single molecules of rhodamine-6G had a transit time of 1.8 ms through the 11 pL probe volume. At 2 × 10−14 M, the probability of a molecule being in the 11 pL probe volume is ∼0.1. Analysis of the data indicates that the signal-to-noise ratio for the detection of a single molecule of rhodamine-6G is ∼1.