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Raman fingerprint for insecticide detection
24 May 2010
Chinese scientists can detect trace concentrations of a hazardous insecticide using gold nanoparticles to boost its spectroscopic fingerprint.
Insecticides are pervasive and potent chemicals which can be problematic in the environment even at low concentrations. Methyl parathion is an insecticide widely used for the control of sucking and chewing insects. While there are a number of methods for its detection in samples such as soil, groundwater and food, a compromise must be reached between sensitivity, selectivity, cost and ease of use.
Jin Wang and colleagues at the Chinese Academy of Sciences, Anhui, have demonstrated a fast, sensitive and practical approach for detecting methyl parathion. They synthesised gold nanoparticles and modified the surface with mono-6-thio-beta-cyclodextrin using the strong interaction between gold and sulphur. The cyclodextrin is well suited to bind the insecticide molecules and hold them in close proximity to the gold surface.
Cylcoldextrin helps bind the insecticide to the gold nanoparticles
Wang's detection method applies a well known form of vibrational spectroscopy called surface enhanced Raman scattering (SERS). A SERS experiment detects the light scattered off a molecule near to a nanoscale noble metal surface. The gold nanoparticles act like lightning rods, amplifying the incoming and outgoing photons, which boosts the intensity of the insecticide's vibrational signals.
'Different molecules have inherent vibrational bands with different positions, intensities and envelopes, which can act as fingerprint peaks,' explains Wang. This means the insecticide can be easily identified in trace amounts. Methyl parathion binds to Wang's modified nanoparticles significantly better than to unmodified ones, producing a SERS signal thousands of times stronger.
The sensitivity of Wang's detection method is reliant upon the strong and selective interaction between the cyclodextrin and methyl parathion. 'The molecules act like a lock and key: methyl parathion is just the right size to fit into the pocket formed by the cyclodextrin,' according to Douglas Stuart, a US chemist at the University of West Georgia who specialises in SERS.
Wang's group is now investigating alternatives to cyclodextrin for SERS detection of other insecticides, explosives and persistent organic pollutants.
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Link to journal article
Synthesis of novel decorated one-dimensional gold nanoparticle and its application in ultrasensitive detection of insecticide
Jin Wang, LingTao Kong, Zheng Guo, JingYao Xu and JinHuai Liu, J. Mater. Chem., 2010, 20, 5271
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