title: Dispersion of a Nanoliter Bolus in Microfluidic Co-Flow.
abstract: Microfluidic systems enable reactions and assays on the scale of nanoliters. However, at this scale nonuniformities in sample delivery become significant. To determine the fundamental minimum sample volume required for a particular device, a detailed understanding of mass transport is required. Co-flowing laminar streams are widely used in many devices, but typically only in the steady-state. Because establishing the co-flow steady-state consumes excess sample volume and time, there is a benefit to operating devices in the transient state, which predominates as the volume of the co-flow reactor decreases. Analysis of the co-flow transient has been neglected thus far. In this work we describe the fabrication of a pneumatically controlled microfluidic injector constructed to inject a discrete 50nL bolus into one side of a two-stream co-flow reactor. Using dye for image analysis, injections were performed at a range of flow rates from 0.5-10μL/min, and for comparison we collected the co-flow steady-state data for this range. The results of the image analysis were also compared against theory and simulations for device validation. For evaluation, we established a metric that indicates how well the mass distribution in the bolus injection approximates steady-state co-flow. Using such analysis, transient-state injections can approximate steady-state conditions within predefined errors, allowing straight forward measurements to be performed with reduced reagent consumption.
authors.affiliation: Bioengineering Center, Charles Stark Draper Laboratory, Tampa, Florida 33612, USA.
authors.forename: A J
authors.initials: AJ
authors.lastname: Conway
authors.affiliation: Bioengineering Center, Charles Stark Draper Laboratory, Tampa, Florida 33612, USA.
authors.forename: W M
authors.initials: WM
authors.lastname: Saadi
authors.affiliation: Bioengineering Center, Charles Stark Draper Laboratory, Tampa, Florida 33612, USA.
authors.forename: F L
authors.initials: FL
authors.lastname: Sinatra
authors.affiliation: Department of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115, USA.
authors.forename: G
authors.initials: G
authors.lastname: Kowalski
authors.affiliation: Charles Stark Draper Laboratory, Cambridge, Massachusetts 02139, USA.
authors.forename: D
authors.initials: D
authors.lastname: Larson
authors.affiliation: Charles Stark Draper Laboratory, Cambridge, Massachusetts 02139, USA.
authors.forename: J
authors.initials: J
authors.lastname: Fiering
keywords: Co-Flow Reactor; Dispersion; Microfluidic Devices; Microfluidics