posted on 2019-06-24, 00:00authored byRobert
B. Channon, Michael P. Nguyen, Charles S. Henry, David S. Dandy
Microfluidic
paper-based analytical devices (μPADs) are simple
but powerful analytical tools that are gaining significant recent
attention due to their many advantages over more traditional monitoring
tools. These include being inexpensive, portable, pump-free, and having
the ability to store reagents. One major limitation of these devices
is slow flow rates, which are controlled by capillary action in the
hydrophilic pores of cellulosic paper. Recent investigations have
advanced the flow rates in μPADs through the generation of a
gap or channel between two closely spaced paper sheets. This multilayered
format has opened up μPADs to new applications and detection
schemes, where large gap sizes (>300 μm) provide at least
169×
faster flow rates than single-layer μPADs, but do not conform
to established mathematical models for fluid transport in porous materials,
such as the classic Lucas-Washburn equation. In the present study,
experimental investigations and analytical modeling are applied to
elucidate the driving forces behind the rapid flow rates in these
devices. We investigate a range of hypotheses for the systems fluid
dynamics and establish a theoretical model to predict the flow rate
in multilayered μPADs that takes into account viscous dissipation
within the paper. Device orientation, sample addition method, and
the gap height are found to be critical concerns when modeling the
imbibition in multilayered devices.