Identification of powdered Chinese herbal medicines by fluorescence microscopy, Part 1: Fluorescent characteristics of mechanical tissues, conducting tissues, and ergastic substances

Abstract

The light microscope has been successfully used in identification of Chinese herbal medicines (CHMs) for more than a century. However, positive identification is not always possible. Given the popularity of fluorescence microscopy in bioanalysis, researchers dedicated to finding new ways to identify CHMs more effectively are now turning to fluorescence microscopy for authentication purposes. Some studies on distinguishing confused species from the same genus and on exploring distributions of chemicals in tissues of CHMs by fluorescence microscopy have been reported; however, no systematic investigations on fluorescent characteristics of powdered CHMs have been reported. Here, 46 samples of 16 CHMs were investigated. Specifically, the mechanical tissues including stone cells and fibers, the conducting tissues including three types of vessels, and ergastic substances including crystals of calcium oxalate and secretions, in various powdered CHMs were investigated by both light microscope and fluorescence microscope. The results showed many microscopic features emit fluorescence that makes them easily observed, even against complex backgrounds. Under the fluorescence microscope, different microscopic features from the same powdered CHM or some same features from different powdered CHMs emitted the different fluorescence, making this information very helpful for the authentication of CHMs in powder form. Moreover, secretions with unique chemical profiles from different powdered CHMs showed different fluorescent characteristics. Hence, fluorescence microscopy could be a useful additional method for the authentication of powdered CHMs if the fluorescent characteristics of specific CHMs are known.

Microscopic characterization of five Artemisia crude herbs using light microscopy, scanning electron microscopy, and microscopic quantitative analysis

“…All dried leaves of the five species were crushed into powder using a grinder and passed through a 100‐mesh sieve (bore diameter of 0.150 mm). The crushed samples were permeabilized with chloral hydrate and sealed with diluted glycerin for observation (Chang et al, 2021; Wang, Liang, et al, 2011). Ten different slides of powdered samples were examined using an ordinary and polarized light microscopy.…”

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“…Many herbal tissues, by virtue of their chemical structures or secondary metabolites, have the ability to emit light of a specific wavelength following the absorption of light with a shorter wavelength and higher energy 25 . For example, in recent years, the fluorescence microscope has been applied to distinguish the medicinal herb Oldenlandia diffusa from other species of the same genus which are confused with it, in herbal markets 26 .…”

Discrimination of Dendrobium officinale and Its Common Adulterants by Combination of Normal Light and Fluorescence Microscopy

“…Fluorescence microscopy is a fast and simply method, which allows less-experienced personnel to identify botanical raw materials. The combination of normal light and fluorescence microscopic technique, which enhanced the accuracy and convenience of identification, has been successfully applied in authentication and quality evaluation of Chinese herbal medicines [17,18,19,20]. The present study focuses on the microscopy technique, combining normal light and fluorescence microscopy, for discrimination of D. officinale and its commonly adulterants, including D. devonianum , D. aphyllum and D. gratiosissimum .…”