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.

To read more: M. Perez et al., Raman Spectroscopy an Option for the Early Detection of Citrus Huanglongbing. Applied Spectroscopy 2016, Vol. 70(5) 829–839.