Volatile Detection from Plant Headspace with Modified Surface-Enhanced Raman Spectroscopy
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abstract
Volatile organic compounds (VOCs) are a potential means of determining plant stresses like insect infestation. Various methods have been developed to analyze volatile compounds. Two representative methods have been commercialized: gas chromatography mass spectrometry (GC/MS) and electronic-nose (E-nose). However, all commonly used methods are unsuitable for accurate detection of VOCs within a short response time. In this study, Raman spectroscopy was tested as an alternative method to accurately determine VOCs and classify their concentrations quickly. One monoterpene, linalool, a known volatile organic compound emitted from many plants, was chosen as a VOC of interest. The samples containing linalool in different concentrations, including the volatile sample collected from a liquid drop of linalool with Tenax-TA adsorbent, were prepared to compare standard Raman spectroscopy with surface-enhanced Raman spectroscopy (SERS). One comparison tested whether Ag-nanoparticles could be transferred from the water phase to the organic solvent phase for SERS application. The other comparison tested the spectra according to the concentration with standard Raman against the sample with transferred Ag-nanoparticles to see the effect of the particle for SERS application. First, the results showed that the water-dispersible Ag-nanoparticle can be transferred into an organic solvent phase with the help of a cationic surfactant. Second, SERS proved to be 5 to 10 times more sensitive than standard Raman at the regions of interest. Therefore, the proposed method which combines volatile sampling with adsorbents and SERS can be considered a preferable tool to standard Raman for fast volatile screening.
