(177w) Pd@Pt Nanoparticle-Amplified Immunoassay for Rapid Detection of Harmful Herbicides

Pd@Pt Nanoparticle-Amplified
Immunoassay for Rapid Detection of Harmful Herbicides

Eunice Y. Kwon^a,
Xiaofan Ruan^b, Limin Wang^b, Yuehe Lin^b, Dan Du^b
and Bernard J. Van Wie^a*

^aVoiland
School of Chemical Engineering & Bioengineering, Washington State
University

^bSchool
of Mechanical and Material Engineering, Washington State University

*Corresponding author, Tel.: +1-509-335-4103; E-mail
address: bvanwie@wsu.edu

In this presentation,
results will be shown on an innovative method of detecting small amounts of
harmful herbicides in the environment. Tests for the most commonly used
herbicides in the United States are the focus of this presentation; we will explore
the benefits of immunoassays that involve the use of Pd@Pt nanoparticles as the
signal-amplifying agent.

Herbicides are widely
used to control unwanted plants in the United States; however, the
Environmental Protection Agency (EPA) has issued warnings about their usage. The
maximum contamination of atrazine in drinking water is 3 ppb because of its
reported potential toxic health effects on exposed humans; congestion of the heart, lungs and kidneys, low
blood pressure, muscle spasms, weight loss, and cancer can result from exposure. Acetochlor is an herbicide often used
in place of atrazine because of its superior biodegradability; however, it has also
been reported to have potential clastogenic effects on human lymphocytes. Therefore,
developing efficient low-cost ways for detecting small amounts of these chemicals
in water is crucial.

To create a
more sensitive and stable test for herbicides, we use two established methods and
introduce a new type of peroxidase-like nanoparticle to improve sensitivity and
stability. The enzyme-linked immunosorbent assay (ELISA) is one of the most
prevalent and useful methods for detecting antigens such as herbicides and pesticides
through immunoreactions with antibodies due to its high sensitivity,
specificity, and efficiency. However, the assay typically requires a separate
application of a secondary antibody linked to an enzyme such as horseradish
peroxidase, which catalyzes conversion of a non-colored organic substrate to a
colored product for detection. In addition, conducting ELISAs is time consuming
and requires a wet chemistry laboratory with a pipetting station, abundant
solutions and a plate reader. To replace ELISAs, we use a lateral flow immunoassay
(LFIA). An LFIA system —also called a “test strip” or an immunochromatographic
assay—offers a one-step rapid detection method and the strip itself is stable
and have a long shelf life. Colloidal nanogold is the most widely used metal in
LFIAs due to its stability, but this nanoparticle has low sensitivity for detecting
lower concentrations of organic residues.

In this study,
we synthesized Pd@Pt nanoparticles that can be bound directly to a primary
antibody, thereby eliminating one step in an ELISA-like process,
and tested these particles in an LFIA. Pd@Pt nanoparticles have peroxidase-like
catalytic activity to oxidize 3,3',5,5'-tetramethylbenzidine while reducing
hydrogen peroxide. This characteristic allows herbicide detection with a spectrophotometer
through this ELISA-like procedure. Additionally, the Pd@Pt nanoparticles create
a clearly visible black line that allows bare-eyed detection when using the LFIA.
Furthermore, this nanoparticle has pH and temperature stability, which increases
both its reliability in altered conditions and its shelf-life.

Using an ELISA-like
format with Pd@Pt nanoparticles, we obtained a limit of detection (LOD) of 0.5
ppb for atrazine. We then applied the method to samples of well water and pond
water that were spiked with atrazine to detect contamination levels of 5, 10,
and 20 ppb. Our tests yielded recoveries of 88 ~ 118 %, offering strong
supporting evidence that atrazine and other herbicides can be detected by the use of peroxidase-like Pd@Pt nanoparticles in an
ELISA-like format. We also used the Pd@Pt nanoparticles on a multiplex test
strip to detect atrazine and acetochlor simultaneously. Our findings suggest
that innovations in efficiency, sensitivity, and stability are possible in tests
for harmful chemicals in the environment. Future tests may be more
cost-effective while offering more rapid results.

Keywords: Biosensors/
Devices, Nanomaterials, Food (Sustainability & Environment)