June 18 2017 by Drew Haser

HOW MUCH PESTICIDE ARE YOU EATING?

In order to feed the growing global population and improve crop yields pesticides are routinely blanketed over agricultural fields. This is despite studies linking pesticides to numerous health issues from mild headaches and nausea to serious chronic incidents of cancer, reproductive harm, and endocrine disruption. Because of their continued use, toxic pesticides have found their way into our air, soil, water, food, and even breast milk of nursing mothers.

The Environmental Protection Agency (EPA) sets tolerances, or maximum residue limits, for pesticides, however, detection remains a burden. This is largely due to the current chromatographic analytical techniques which require expensive equipment operated by highly-skilled technicians in specialized laboratories. This may all be changing soon as new highly sensitive and simple to use nanoparticle-based pesticide sensors are developed.

 'BAND-AID LIKE' SENSOR POWERED BY NANOPARTICLES

A new study from researchers at State Key Laboratory of Optoelectronic Materials and Technologies in China has revealed the possibility for flexible sensors capable of in-situ detection of pesticides at the nanogram level.

According to study co-author Hao Cui, “We have successfully synthesized flexible, transparent, and self-standing Silicon Nanowire Paper (SiNWP) consisting of ultrathin three-dimensional silicon nanowire networks.

“The excellent flexibility and unique architecture of the SiNWP have great potential for various flexible functional devices applications. In our current study, we continue to explore the potential application of the SiNWP as flexible and self-standing SERS substrates that can be universally adapted onto warping surfaces for in situ and nondestructive identification and detection.”

By forming hybrids with gold nanoparticles (AuNPs) on the silicon nanowires, the researchers were able to obtain even stronger optical response via synergistic interactions between the dielectric silicon and gold components while maintaining flexibility.

Unlike traditional Surface Enhanced Raman Scattering (SERS) substrates that are rigid, the AuNP-SiNWP 'band-aid like' flexibility allows for greater contact area and improved adsorption of the pesticide molecules on a curved surface. Once a toxin is bound to the sensor it alters the surface plasmon resonance which can be measured using SERS. This spectral shift is used to identify the presence of toxins and, in fact, each pesticide produces a unique “fingerprint” in the spectral shift it produces.

IMPROVED SENSITIVITY, BETTER DETECTION

To demonstrate the improved sensitivity the researchers wrapped their sensor on the surface of lemons with various amounts of a commonly used pesticide, thiram.

The results as explained by Hao Cui were highly encouraging, “We showed that by directly wrapping the AuNP–SiNWP onto the lemon surface, the lowest concentration of the pesticide residues detected can be down to 72 ng/cm2, which was far less than the permitted dose in food safety.”

Detection at this level is equivalent to identifying a single grain of salt in an average sized box of cereal. Compared to current detection standards set in micrograms, this level of sensitivity is orders of magnitude better, and can be achieved with a simple Raman spectrometer instead of expensive analytical equipment and lab space.

As the nanoparticle sensor technology continues to evolve it provides hope for a new way of judging the food we eat and ideally healthier diets and lives.

More Information: Cui, Hao, et al. "Flexible, Transparent, and Free-Standing Silicon Nanowire SERS Platform for in Situ Food Inspection." ACS Sensors 2.3 (2017): 386-393. DOI: 10.1021/acssensors.6b00712

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