Digital Chemical Analysis of Dilute Microdroplets
K.C. Ng, W.B. Whitten, J.M. Ramsey and S. Arnold
Anal. Chem. 64, 2914-2919(1992)

The concept of digital molecular detection, the ability to count individual molecules, is described and the mathematical framework for defining detection limits under various experimental
constraints presented. We show that with modest signal-to-noise ratio for detection of single molecules, significant advantages accrue when using a digital detection strategy versus a conventional approach. Concentration detection limits decrease inversely with total sample volume for digital detection versus reduction as the inverse square root for conventional measurements. This advantage could yield detection limit that are reduced by orders of magnitude if sample volume is limited. In addition, we present experimental results demonstrating the concept of digital molecular detection using B-phycoerythrin molecules and levitated microdroplet fluorlmetry. Single B-phycoerythrin molecules are detected with a signal-to-noise ratio greater than 4.