Dispersion of a nanoliter bolus in microfluidic co-flow

• Published in: Journal of micromechanics and microengineering 2014-03, Vol.24 (3), p.034006-11
• Main Authors: Conway, A J, Saadi, W M, Sinatra, F L, Kowalski, G, Larson, D, Fiering, J
• Format: Article
• Language: English
• Subjects: Approximation; Biological and medical sciences; co-flow reactor; Consumption; Devices; dispersion; Drug delivery systems; Image analysis; Medical sciences; microfluidic devices; Microfluidics; Nanostructure; Radiotherapy. Instrumental treatment. Physiotherapy. Reeducation. Rehabilitation, orthophony, crenotherapy. Diet therapy and various other treatments (general aspects); Reactors; Technology. Biomaterials. Equipments. Material. Instrumentation
• ISSN: 0960-1317; 1361-6439
• DOI: 10.1088/0960-1317/24/3/034006

Microfluidic systems enable reactions and assays on the scale of nanoliters. However, at this scale non-uniformities 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 50 nL 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 0.5-10 µL min−1, 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 pre-defined errors, allowing straightforward measurements to be performed with reduced reagent consumption.