Characterization and Identification of Fungal Conidia via Shifted Excitation Raman Difference Spectroscopy

Abstract

Fungi can be found everywhere, and their impacts on human beings are numerous and varied. Fungi have been widely used in the food, biofuel, beverage and pharmaceutical industries. 1 However, uncontrolled fungal growth can be costly to agriculture, forestry and livestock. If they feed on humans, diseases can be induced such as ringworm, athlete’s foot and lung infections. Some effects on human health may last over years and even lifetimes. 2 It requires timely and accurate identification of mold species to evaluate and/or prevent damage from mold growth, and minimize the consequences of mold exposure. Raman spectroscopy studies on mold spores have been proposed and implemented as a method to identify fungal species. However, the presence of fluorescence emission always hinders Raman signal detection and is virtually impossible to avoid, especially in biological specimens. Shifted excitation Raman difference spectroscopy (SERDS) is a very powerful technique to separate Raman contribution from fluorescence contribution. Herein, we adopt the SERDS modality to extract pure Raman signals from fungal conidia of different species and find that Raman signatures of spores generated from pigment molecules bounded within the cell walls. 3 A further study of conidia of different mold species indicates that the major features of the Raman spectrum correlate with the melanin biosynthesis pathway: species that produce the same melanin exhibit similar Raman spectra. 4 , 5