Pheromone Detection by Raman Spectroscopy

Raman spectroscopy has allowed for the acquisition of Raman signatures for pheromone components, or chemicals, which are found in the pheromones of crop key pests: ( Z, Z)-11,13- Hexadecadienal, (Z, Z, Z, Z, Z) and (3,6,9,12,15)-Tricosapentene for Naval Orange Worm, NOW, moth affecting tree nuts, and (E, Z)-7,9-Docedadien-1-yl Acetate (European Grapevine, EVG, moth). Raman signatures were successfully extracted, and peaks were assigned to different vibration and rotational modes for each primary chemical. Notably, the signatures of these primary chemicals are very unique, which not only confirms the ability of Raman to detect these chemicals, but to also differentiate between them. The sensitivity of the system's ability to detect these chemicals at very low concentrations was evaluated. Starting with 100% pure concentrated chemicals, series of dilutions were performed, testing various concentrations down to 0.1%, in both ethanol and acetone. Similar trends and peaks were observed, but with different intensities, the solvent being the only difference. Characterization of singular signatures standalone and in mixtures is conducted using Principal Component Analysis (PCA) as a way to ease separation. Principal component analysis is a multivariate data analysis technique, which allows for the better understanding of numerous factors which affect the spectral variation across different samples. A new set of axes, or principal components, are aligned with the maximum directions of variance inside of a data set. Scores, loadings, and residuals become the new matrices which are created through his method of analysis. By using the principal component analysis technique complex Raman spectra were successfully interpreted by revealing compounds and differences between each sample.