A microfluidic mixing system for single-molecule measurements.

This article describes the design and fabrication of a microfluidic mixing system optimized for ultrasensitive optical measurements. Channels are replica-molded in polydimethylsiloxane elastomer and sealed with fused-silica coverglass. The resulting devices have broad chemical compatibility and extremely low fluorescence background, enabling measurements of individual molecules under well-characterized nonequilibrium conditions. Fluid delivery and pressure connections are made using an interface that allows for rapid assembly, rapid sample exchange, and modular device replacement while providing access for high numerical aperture optics.