Digital concentration readout of single enzyme molecules using femtoliter arrays and Poisson statistics

Nano Lett. 2006 Mar;6(3):520-3. doi: 10.1021/nl060227d.


Methods for accurately quantifying the concentration of a particular analyte in solution are all based on ensemble responses in which many analyte molecules give rise to the measured signal. In this paper, single molecules of beta-galactosidase were monitored using a 1 mm diameter fiber optic bundle with 2.4 x 10(5) individually sealed, femtoliter microwell reactors. By observation of the buildup of fluorescent products from single enzyme molecule catalysis over the array of reaction vessels and by application of a Poisson statistical analysis, a digital concentration readout was obtained. This approach should prove useful for single molecule enzymology and ultrasensitive bioassays. More generally, the ability to determine concentration by counting individual molecules offers a new approach to analysis of dilute solutions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biological Assay
  • Fiber Optic Technology
  • Indicator Dilution Techniques
  • Microchemistry / methods*
  • Optical Fibers
  • Poisson Distribution
  • Protein Array Analysis
  • beta-Galactosidase / analysis*
  • beta-Galactosidase / metabolism


  • beta-Galactosidase