Temporal Optimization of Microfluidic Colorimetric Sensors by Use of Multiplexed Stop-Flow Architecture

We present two microfluidic architectures (continuous flow and multiplexed stop flow) for miniaturized colorimetric nutrient sensors. These systems are compared with respect to the temporal response (for optimization of sampling rate) and reduction of reagent consumption. The continuous-flow system is capable of a sampling rate of 60 samples·h–1, limited by Taylor dispersion. The novel multiplexed stop-flow (MSF) microsystem architecture is not limited by dispersion. A demonstration MSF system consisting of two stop-flow channels is presented. This requires 12.6 s to load each sample into a measurement channel and when scaled would be capable of a throughput of 285 h–1 (with full color development). The MSF architecture is manufactured in PMMA/Viton/PMMA [where PMMA = poly(methyl methacrylate)], utilizes on-chip valving, and is scalable, thereby permitting sampling at much faster rates (subsecond). Either system is capable of remote deployment and continuous measurement of nutrient concentrations. The MSF system is particularly suited for applications requiring high temporal or spatial resolution; such as from moving vehicles.