Identification of aqueous pollen extracts using surface enhanced Raman scattering (SERS) and pattern recognition methods

Abstract

Aqueous pollen extracts of varying taxonomic relations were analyzed with surface enhanced Raman scattering (SERS) by using gold nanoparticles in aqueous suspensions as SERS substrate. This enables a selective vibrational characterization of the pollen water soluble fraction (mostly cellular components) devoid of the spectral contributions from the insoluble sporopollenin outer layer. The spectra of the pollen extracts are species-specific, and the chemical fingerprints can be exploited to achieve a classification that can distinguish between different species of the same genus. In the simple experimental procedure, several thousands of spectra per species are generated. Using an artificial neural network (ANN), it is demonstrated that analysis of the intrinsic biochemical information of the pollen cells in the SERS data enables the identification of pollen from different plant species at high accuracy. The ANN extracts the taxonomically-relevant information from the data in spite of high intra-species spectral variation caused by signal fluctuations and preparation specifics. The results show that SERS can be used for the reliable characterization and identification of pollen samples. They have implications for improved investigation of pollen physiology and for allergy warning.

Chemical Analysis of Pollen by FT-Raman and FTIR Spectroscopies

“…Vibrational studies of pollen, by diverse infrared and Raman techniques, have shown that vibrational spectroscopy achieves economical and rapid identification and classification of pollen according to taxonomy and phylogenetic relationship (Pappas et al, 2003;Ivleva et al, 2005;Gottardini et al, 2007;Schulte et al, 2008;Dell'anna et al, 2009;Zimmermann, 2010Zimmermann, , 2018Guedes et al, 2014;Zimmermann and Kohler, 2014;Zimmermann et al, 2015b;Julier et al, 2016;Seifert et al, 2016;Woutersen et al, 2018;Jardine et al, 2019;Mondol et al, 2019). For example, the recent FTIR microspectroscopy study on individual pollen grains has achieved more accurate classification than optical microscopy, which is the benchmark method in pollen identification (Zimmermann et al, 2016).…”

Combining Chemical Information From Grass Pollen in Multimodal Characterization

“…Vibrational spectroscopic methods, such as FTIR (Pappas et al, 2003;Gottardini et al, 2007;Dell'Anna et al, 2009;Julier et al, 2016;Depciuch et al, 2018;Jardine et al, 2019), Raman scattering (Ivleva et al, 2005;Schulte et al, 2008), and surface enhanced Raman scattering (SERS) (Sengupta et al, 2005;Seifert et al, 2016), as well as mass spectrometric methods (Krause et al, 2012;Lauer et al, 2018) can be applied to classify pollen according to taxonomic relationships based on molecular composition. Pollen spectra can also indicate changes in chemical composition according to genetic background and environmental influences (Zimmermann and Kohler, 2014;Zimmermann et al, 2017;Diehn et al, 2018).…”

“…Surface-enhanced Raman scattering (SERS), in turn, gives very strong signals from pollen constituents that must interact with metal nanoparticles, i.e., the SERS substrate, and although it enables the investigation of less abundant molecular species, it has a high selectivity for specific classes of molecules. This can be the water-soluble pollen fraction, extracted in a facile way (Seifert et al, 2016) or the sporopollenin polymer after embedding the SERS nanoparticle substrate inside the nanoscopic cavities of the pollen shell (Joseph et al, 2011).…”

Physiological influence of silica on germinating pollen as shown by Raman spectroscopy

“…The germination conditions for pollen grains are easy to adjust , and, focusing on different histological features and different pollen species, a comparison of the effects of variations in growth conditions for one pollen species can be achieved. In previous work, our and other groups have shown that Raman spectroscopy can serve as a method to characterize pollen grains under varying conditions , to image their biochemical composition , and to investigate the process of germination .…”