I was reading a great article today in Applied Spectroscopy about a novel application of Raman spectroscopy. Apparently there is a disease called Huanglongbing (HLB) or ‘Citrus Greening Disease,’ which threatens a large portion of the global citrus crop. The way that this disease is currently detected is via a costly DNA analysis, because symptoms of the disease are otherwise easily confused with nutritional deficiencies or other maladies. Between 2009 and 2014, Mexico alone invested over $75 million USD in detection and control.
The paper reports the first use of Raman to successfully detect HLB. The authors, Perez et al., used a portable Raman device in conjunction with principal components analysis (PCA) and linear discriminant analysis (LDA) to evaluate spectra from the leaves of 116 citrus trees, a combination of orange and lime trees. Only the first two principal components were used – thus the dimensionality of the problem was substantially reduced. On the PC plot (PC1 versus PC2) there was a clear division that allowed LDA to perform quite well as a screening method. The authors report overall that the method showed a sensitivity of 86.9%, a specificity of 91.4%, and a precision of 89.2% in discriminating healthy and HLB-positive plants. as confirmed by laboratory analysis. This suggests an incredible potential time and cost savings over DNA analysis.