Currently, paper devices
including paper strip tests, paper-based assays, and paper-based
microfluidics are attractive for portable point-of-measurement
(POM) monitoring and on-site detection due to advantages which
include low cost, portability, ease of use, high speed, and low
reagent and sample consumption [2–4]. Furthermore, paper
provides a high surface area/high optical contrast substrate for
colorimetric detection. Paper devices are also suited for use by
nontechnical personnel. Finally, paper devices are made from
naturally abundant, biodegradable and inexpensive materials (i.e.,
cellulose) [5,6]. Most commercial paper devices use colorimetric
detection and have been applied for qualitative and/or semiquantitative
analyte detection [1,7–11]. For colorimetric sensing,
analyte flow is directed along the paper matrix by capillary action,
and analyte then reacts with a label or organic dye in the test
zone. The assay results are quantified by comparing the color
hues and/or intensities generated by unknown analytes to known
analyte concentrations. Nontechnical personnel can interpret the
result by the naked eye in many cases. Paper devices therefore do
not require external instrumentation for interpretation or
mechanical forces to drive flow.