10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
A Newly Developed, Inexpensive Single-Particle Fluorescence Spectrometer: Characterization and Application to Pollen Analysis
BENJAMIN E. SWANSON, Sam Scherer, Samir Rezgui, Donald R. Huffman, J. Alex Huffman, University of Denver, CO
Abstract Number: 1567 Working Group: Bioaerosols
Abstract Primary biological aerosol particles (PBAP) are ubiquitous throughout the Earth’s atmosphere and play diverse roles in environmental systems, biological process, climate, and even human health. Bioaerosol detection in the atmosphere has historically been a time-consuming, manual process. Within the last several decades, many laser-/light-induced fluorescence (LIF) instruments have become commercially available for bioaerosol analysis. Even so, the majority of widespread identification techniques still rely on complicated analysis, as commercial instruments frequently have trouble classifying beyond broad classes of bioaerosol types (e.g. fungal spores versus pollen), and those that can perform this task are usually very expensive. Pollen-counting, for example, is frequently still accomplished via manual visual microscopy due to the costly nature or low spectral quality of UV-LIF technologies.
Here we discuss a technique we recently introduced to analyze many individual particles collected onto a glass substrate utilizing multiple excitation sources [1]. Our previous characterization work assessed the ability of the instrument to probe relevant biofluorophores within standard particles and several species of pollen used as examples [2]. Four excitation sources (280 nm, 350 nm, 405 nm, and 450 nm) were matched with emission maxima previously shown to be important for a large variety of pollen species [3]. The instrument described here can provide a quick, binary assessment of whether particles are either fluorescent or non-fluorescent, similar to the way certain commercial single-particle UV-LIF instruments are operated. Additionally, the instrument can provide resolved fluorescence spectra of individual particles at ca. 2 nm resolution. As a part of the characterization work to be shown, a method was developed to correct for defects in the inexpensive optical components and for differences in laser and LED source emission profiles. These calibration methods enable the collection of fluorescence spectra approximately normalized by particle size to help show differences in particle composition in an effort to differentiate between particle types. Despite its limit to detection of emission of wavelengths longer than 400 nm (due to limitations in the CCD detector) the instrument can confidently distinguish between species of pollen particles when employing a clustering algorithm [2]. Both K-means and Hierarchical Clustering Analysis (HAC) have been probed as possible methods of distinguishing between particles. Work has also been undertaken for automatic particle identification via a machine learning algorithm, which has shown promising results toward considerably higher particle analysis throughput.
A number of pollen species (>10) were analyzed using the clustering method, inputting full detected emission spectra (400-700 nm) and particle size measured by the instrument into a clustering algorithm. The eventual goal is to further develop a prototype handheld version of the instrument to be deployed wherever pollen or mold-spore counting and differentiation is required. This technique has demonstrated proof-of-concept ability to supplement the current host of bioaerosol LIF instrumentation at a much lower purchase-cost, while also retaining high fluorescence spectral resolution and the long-range potential to serve as a pollen-counting instrument.
References: [1] D. R. Huffman, B. E. Swanson, and J. A. Huffman, “A wavelength-dispersive instrument for characterizing fluorescence and scattering spectra of individual aerosol particles on a substrate,” Atmos. Meas. Tech. 9(8), 3987–3998 (2016). [2] B. E. Swanson and J. A. Huffman, “Development and characterization of an inexpensive single-particle fluorescence spectrometer for bioaerosol monitoring,” Opt Express 26(3), (2018). [3] C. Pöhlker, J. A. Huffman, and U. Pöschl, “Autofluorescence of atmospheric bioaerosols: Spectral fingerprints and taxonomic trends of pollen,” Atmos. Meas. Tech. 6(12), 3369–3392 (2013).