Comparison of Different Methods for the Detection of Silica Inclusions in Plant Tissues

Abstract

There is no standardized method to detect silica depositions in plant tissues. Therefore, we compared current methods to reveal their advantages and disadvantages for selecting the most suitable method. We studied three plant species (Equisetum hyemale, Carex pendula, and Miscanthus sinensis) with pronounced and well-defined silica inclusions of different forms. We used two SEM methods, two stainings for light microscopy, and Raman imaging. Our results showed that energy-dispersive x-ray (EDX) analysis is highly specific but has a lower resolution than low-voltage–high-contrast (vCD) detection, which gives good resolution and a broad scanning area. In addition to the nonspecificity of vCD detection, it can be difficult to identify silica coatings with this method because of a lack of contrast with non-silica-coated tissues. Therefore, confirmation of silica detection with EDX is needed. In all plants tested, staining proved to be not silica specific but did allow for an indication of the position of silica inclusions, facilitating later, more specific analysis. Silica detection via Raman imaging might be affected by interference, depending on the sample, but it is the sole method tested that allows for distinguishing different types of silica inclusions chemically. A combination of EDX and vCD analysis provides the best results for locating the exact position of silica inclusions.