Microfabricated arrays of femtoliter chambers allow single molecule enzymology

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Abstract
Precise understanding of biological functions requires tools comparable in size to the basic components of life1,2,3,4. Single molecule studies have revealed molecular behaviors usually hidden in the ensemble- and time-averaging of bulk experiments5,6. Although most such approaches rely on sophisticated optical strategies to limit the detection volume7,8, another attractive approach is to perform the assay inside very small containers9,10,11,12,13,14,15,16. We have developed a silicone device presenting a large array of micrometer-sized cavities. We used it to tightly enclose volumes of solution, as low as femtoliters, over long periods of time. The microchip insures that the chambers are uniform and precisely positioned. We demonstrated the feasibility of our approach by measuring the activity of single molecules of β-galactosidase and horseradish peroxidase. The approach should be of interest for many ultrasensitive bioassays at the single-molecule level.