Application of Micro- and Nano-Spectroscopic Techniques for Systematic Studies of Surface Features of the Barley Leaf Cuticle

In this study, micro- and nanospectroscopic techniques were used to examine the aerial epidermis of a barley crop leaf cuticle to determine if there is a correlation between aerial morphological features and their chemistry. We believe this understanding may inform the design of nanoparticles (NPs) with improved and controlled NP-plant interactions and potential applications as foliar nanofertilizers. We compared three different Raman excitation wavelengths-NIR, Vis, and UV- and evaluated the possibilities of nanospectroscopic techniques like tip-enhanced Raman spectroscopy (TERS) and nano-FTIR spectroscopy. All measurements were performed on a fresh leaf surface. The impact of excitation wavelength and other measurement parameters (laser power, exposure time) to obtain an optimal signal-to-noise ratio without photodamaging the leaf was systematically evaluated. The main compounds detected in the cuticle matrix were carotenoids, flavonoids, polysaccharides, phenolic compounds, and cuticular waxes. UV (325 nm) was found to be the most suitable excitation wavelength for obtaining the most intense signals from the cuticle while avoiding plant pigment signals.