Human exposure to heavy metals is a concerning global
problem because
of its detrimental effect on our health and ecosystem. Assessing the
levels of these metals is cost- and labor-intensive and nonuser friendly
because current analysis approaches typically rely on heavy instrumentations
like inductively coupled plasma-mass spectrometry, which is only possible
in centralized labs. Hence, simple economical detection methods are
in high demand in developing countries and areas with insufficient
infrastructure, professional experts, and appropriate environmental
treatment. Several microfluidic paper-based analytical devices have
been reported as promising alternatives to conventional testing methods
for on-site heavy metal detection. Paper-based microfluidics are advantageous
because of their simple fabrication, biodegradability, low cost, and
ability to operate without pumps. However, typical assay times for
current platforms are slow, and they typically rely on pipetting a
fixed volume into the assay cards. This adds complexity in actual
field scenarios. Here, we report a novel, inexpensive, and straightforward
capillary-driven microfluidic device combined with paper for rapid
and user-friendly detection of Ni(II), Cu(II), and Fe(III) in water.
A colorimetric approach was adopted to quantify these metals. The
device was able to produce a homogeneous color signal within 8 s of
sample insertion. The limit of detection and limit of quantification
were calculated to be 2 and 6.67 ppm for nickel, 0.3 and 1 ppm for
Cu, and 1.1 and 3.67 ppm for Fe, respectively. The majority (>90%)
of the collected samples showed recovery in the 80–110% range
with acceptable accuracy and precision (<15% RSD) for a colorimetric
device. This technique can be beneficial for rapidly assessing heavy
metal exposure in drinking and surface water at drastically reduced
assay time and is the first example of capillary flow-driven microfluidic
devices as a transport medium for heavy metal detection.