Identification of single microbial particles using electro-dynamic balance assisted laser-induced breakdown and fluorescence spectroscopy

Abstract

Online characterization of fungal and bacterial spores is important in various applications due to their health and climatic relevance. The aim of this study was to demonstrate the capability of the combination of electro-dynamic balance assisted laser-induced breakdown spectroscopy (LIBS) and laser-induced fluorescence (LIF) techniques for the online detection of single fungal spores (Aspergillus versicolor and Penicillium brevicompactum) and bacteria (Bacillus aureus). The method enabled sensitive and repeatable LIBS analysis of common elemental components (Ca, Na, and K) from single microbial particles for the first time. Significant differences in the concentrations of these elements were observed between the species, e.g., bacterial spores had over three orders of magnitude higher Ca concentration (2 £ 10 ¡12 g/particle) compared to fungal spores (3-5 £ 10 ¡16 g/particle). The LIF analysis has previously been used to distinguish bioaerosols from other aerosols due to their fluorescence ability. This study showed that combination of LIF and LIBS analysis is a promising tool for identification of different bioaerosol particle types. EDITORPaul J. Ziemann

Real-time sensing of bioaerosols: Review and current perspectives

“…The electronic emission from the electronic excited states provides elemental composition of the particle, which can be characteristic of individual material types. LIBS capability provides an orthogonal measurement technique that is proven to improve the false alarm rate of bioaerosol sensors based on fluorescence; however, it does not offer enough discrimination as a standalone technique due to the abundance of detected elements in the environment and the high variability in signal strength due to non-uniformity of the plasma formed (Hybl et al 2006;Martin, Cheng, and Martin 1999;Saari et al 2016). A similar technique of sparkinduced breakdown spectroscopy (SIBS b ; not to be confused with the fluorescence technique with matching acronym) determines elemental composition, but using energy input from an electrically sparked plasma, which offers a cost-effective alternative to LIBS (Tysk, D'angelo, & Herzog 2015).…”

Toward elemental analysis of ambient single particles using electrodynamic balance and laser-induced breakdown spectroscopy

“…However, the initial droplet size is usually in the size range of tens of micrometers, (e.g., Berglund and Liu 1973;J€ arvinen and Toivonen 2016;Udey, Jones, and Farquar 2013), meaning that with a 1 mm residual particle the possible impurities in the carrier liquid condensate with a factor of 10 3 -10 6 considering mass. Thus, when measuring from a dropletgenerated source, the spectrum from "pure" droplet residuals has to be measured as a background reference, as in Saari et al (2016). If the particle contains only small amounts of the elements also present in the contamination source, it might be challenging to detect them from the background signal.…”

“…Water droplets have been focused with a standing acoustic wave (Contreras et al 2018) and with an electrodynamic balance (EDB) trap (J€ arvinen et al 2014). Furthermore, primary particles can be immersed in the water droplets and the dry residuals analyzed with the EDB-LIBS equipment, leading to a single-particle analysis technique (Saari et al 2016). However, droplet generation leaves the residual particles with unwanted contamination from the carrier substance.…”

A review of the use of laser-induced breakdown spectroscopy for bacterial classification, quantification, and identification

“…Of more concern clinically are infectious fungal spores and yeasts [30]. The ability to identify single spores of the fungi Aspergillus versicolor and Penicillium brevicompactum using a novel electro-dynamic balance-assisted online LIBS apparatus with a dual laser-induced fluorescence (LIF) capability has been shown [35]. Significant differences in the concentrations of the very important elements of calcium, sodium and potassium were inferred from differences in the measured LIBS spectra with the LIF analysis adding the ability to rapidly differentiate these bioaerosols from other aerosol types.…”