Session: Analytical Division Poster:

Paper-based microfluidics exploit capillary forces to transport fluids in myriad analytical platforms without the need for externally powered pumps. We present the characterization and set of design rules for paper-based, capillary-driven, disposable pumps for sampling of fluids. These paper pumps can be used in a "set-and-forget" manner, in which the geometric design of the paper pump predetermines the sampling flow rate and total sampled volume. The simple paper pumps consist of a rectangular inlet channel and fan-shaped reservoir. The inlet channel of the paper pump acted as the resistive region in which the flow rate of the pump was determined by the channel aspect ratio. Three variations of the resistive neck inlet region were used with a 1:1, 1:4 and 1:8 width to length ratio to control the flow rate. The fan-shaped reservoir was increased in total surface area to collect different volumes. The variations in geometries scaled the flow rate and sampled volumes, as expected. In addition to the different paper pump geometries, three model fluids were evaluated. The model fluids were aqueous solutions of fluorescent dextran with molecular weights ranging from 3 kDa to 500 kDa. The geometry-controlled flow rates affected the rate at which the model fluids were imbibed; however, the molecular weight of each dextran solution also affected the rate of transport through the pump. The larger molecular weight of the dextran solution resulted in a slower rate of transport through the paper pump. Such separation effects can be attributed to the combination of capillary-forces, diffusion rates, and interaction of the model analyte with the paper matrix. Consequently, the design of such paper pumps must not only consider geometry, but the added co-dependent effects of sampling rate and analyte interactions with the paper matrix.

Omar Mohd

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