Single-Molecule Fluorescence Analysis in Solution

Over the past five years, several groups have developed the capability to detect and identify single fluorescent molecules in solution as the molecules flow through a focused laser beam. The history of the approach to single-molecule detection in fluid solution is shown in Fig. 1. Approximately one dozen molecular species have been detected at this level of sensitivity. Fluorescence-based, single-molecule detection techniques are expected to have a significant impact in fields where fluorescence detection and quantification are broadly applied, e.g., analytical chemistry, biology, and medicine. Single-molecule detection is a new way of doing analytical chemistry, and new applications will arise. In this article, we describe our approach to single-molecule detection and explore assays that can be done at the single-species level that would be difficult or impossible with bulk measurements.