Research
The central mission of the Huffman Group in the Department of Chemistry and Biochemistry at DU is to develop and improve strategies of detection and quantification of biological aerosols and related analytes so that we can apply advanced techniques to field investigations.
This mission is borne out through two guiding questions. First - How do bioaerosols affect Earth system properties? Second - How does protein nitration affect human health? We approach these questions from my perspective as an analytical chemist and an atmospheric scientist. Each research project in my lab follows the path from method improvement toward field investigation and traces directly from one of the two centers summarized below.
Guiding Question 1: How to bioaerosols affect Earth system properties? [17, 43]
As emphasized in the schematic diagram above, the central hub of the work in the Huffman group is toward the first guiding question is the use of single-particle ultraviolet light-induced fluorescence (UV-LIF) instrumentation. In the last two decades there has been a significant effort by government and academic labs to develop UV-LIF instrumentation to detect single bioaerosols, especially possible threat agents, in real-time. In the last 5-10 years there has been an increasing surge of interest within academic research labs to apply these new techniques to questions about the atmosphere and Earth system. It is well known that some types of bacteria and other bioaerosol classes are efficient nucleators of ice at relatively warm temperatures (-15 to -2 oC), well above the -38 oC required before pure droplets of water will freeze. These microorganisms often exist terrestrially as plant pathogens and can influence agriculture and plant health. When they are released to the atmosphere, however, their ability to induce ice formation is hypothesized to influence how mixed-phase clouds (water + ice) form and evolve and therefore how precipitation forms in certain regions (a phenomenon known as the Bioprecipitation Hypothesis, [26]). At a basic level, the geographic and temporal patterns about bioaerosol emission and concentration information are not well understood. This contributes even further uncertainty about how mixed-phase cloud and precipitation patterns may be influenced. Below are several project classes actively being investigated in the Huffman group.
a. WIBS characterization
The Wideband Integrated Bioaerosol Sensor (WIBS) is one of only a few commercially available UV-LIF instruments designed for bioaerosol detection. Its general operating principle is to draw in a continuous flow of air and interrogate individual particles spectroscopically in real-time. Briefly, particles are focused into a narrow beam and pass through a red diode laser. Particles large than ~0.5 µm trigger pulses from two Xenon flash lamps, which excite fluorescence from each particle at 280 nm and 370 nm, respectively. Fluorescent light emitted from each flash is recorded as a total light intensity (not wavelength dispersed) in two channels. The wavelengths of excitation and emission were chosen by instrument developers in an attempt to detect key biofluorophores such as NAD(P)H and riboflavin in one channel and proteins containing tyrosine and tryptophan in another channel in order to selectively highlight airborne biological material [e.g. 18, 24]. A key benefit of the instrument is that it can operate relatively autonomously for weeks at a time in the field, providing information about supermicron-sized aerosol particles continuously at high time and particle size resolution. The Huffman group works closely with many of the leaders in the field of aerosol UV-LIF, and there is general consensus that more work needs to be done to understand how these instruments work, what they can really provide in terms of field information, and how best to analyze the volumes of data created [e.g. 21, 31]. We perform lab experiments to better understand and improve the operation and data analysis related to this class of instrumentation. This work has been led by M.S. student Nicole Savage.
b. Field investigation of bioaerosols and ice nuclei
One effort of our lab has been to deploy the WIBS in collaboration with various partners (especially the Dr. Allan Bertram group at the Univ. of British Columbia) and alongside co-located instrumentation at field sites around the world. We have found success comparing the results from our single-particle fluorescence instruments with techniques that analyze properties of atmospheric ice nuclei (IN) (publication 36]). Our first investigation of this type was at a field site near Woodland Park, Colorado (former M.A. student Carolyn Schumacher; publications [20, 22, 23, 25]) and have since performed follow-up studies: outside Paris, France to look at the influence of the urban air on bioaerosol and IN properties (former undergraduate students Wal Lassar and Kyle Pierce); in rural, coastal British Columbia to investigate the role of ocean bioactivity to marine IN and cloud properties (former M.S. student Yuri Li; publications [33, 38, 39, 40]); on the remote Reunion Island in the South Indian Ocean to further investigate long-range transport of marine aerosol (postdoc David O’Connor, undergraduate student Rachel Wegener); and in both Cyprus and Barbados to investigate the role of long-range Saharan dust transport on bioaerosol and IN properties (M.S. student Nicole Savage and undergraduate student Christine Krentz).
As a separate aspect of several field projects (central Colorado, Cyprus, Barbados) we have collected high-volume filters of total suspended particulate material and performed off-line analyses to investigate molecular tracers of fungal spores and bacteria (publication [44]). M.S. student Marie Gosselin has led these efforts by using High Performance Anion Exchange Chromatography with Pulsed Amperometric Detection (HPAEC-PAD).
The Huffman Group has participated in research around the world, both directly and through collaboration, by collecting and/or analyzing aerosols. Locations of field experiments have included sittes in: Germany [15], Ireland [29], Finland [25, 30], Cyprus, Barbados, Reunion Island, Vancouver Island [33, 37, 38, 39, 40], India [41], remote Amazonia [14, 19], rural Colorado [20, 22, 23, 25, 28, 31, 44], and even in the built/indoor environment [27, 35].
Here is a link to further details regarding Field Projects from Huffman Group activities.
c. Instrument development
The discussion of how best to characterize, calibrate, and utilize single-particle UV-LIF instrumentation led to thoughts about how to improve aspects of the detection process. The WIBS and similar commercial technology provides highly resolved information about particle size and temporal emission patterns. The instrumentation provides almost no spectral resolution (a “spectrum” of two channels) and costs on the order of $100k per unit. As a collaborative effort with Prof. Emeritus Don Huffman from the University of Arizona (Prof. Alex Huffman’s father), the Huffman Group has developed a microscope spectrofluorometer that provides well-resolved (a few nm) fluorescence emission spectra of individual particles collected onto a substrate, each at several excitation wavelengths (publication [42]). This strategy does not provide real-time analysis, but is focused on providing individual particle spectra at a cost reduction of approximately two orders of magnitude, or more. We have a working benchtop version of our instrument in the lab and Ph.D. student Benjamin Swanson is now leading the effort to develop and characterize the technique. This work is patent pending.
Guiding Question 2: How does protein nitration affect human health?
The second motivating question in our lab introduces a fundamentally different set of scientific problems and approaches. Instead of focusing on the environmental effects of bioaerosols, this portion of my group is centered on questions about human health. The original impetus for this set of projects began during my postdoctoral study when I became interested in the idea that proteins on the surfaces of bioaerosols could undergo oxidation and nitration reactions with NO2 and O3 pollutants to produce more allergenic protein products. As stated, our approach has been to develop and improve detection methodologies in order to ask questions about the atmosphere and human health. We now have several maturing projects to develop chemical assays to quantify the extent that proteins haven nitrated on the surfaces of atmospheric bioaerosols and within certain animal tissues.
The original motivation for this section of my lab was literature evidence that showed an enhanced allergenic response when rats were exposed to nitrated pollen proteins instead of the native proteins. Following those studies, nitrated proteins have been found at relatively high levels in limited atmospheric studies. Using a combination of laboratory experiments to improve detection protocols and field study, undergraduate students Emma Biesiada, Kyle Pierce, and Anna Dondero have been working on proteins of atmospheric importance and Ph.D. student Amani Alhalwani has been investigating proteins within the human system. This work has been funded by a combination of fellowships and grants from the Environmental Protection Agency (EPA), the U.S. Army Research Office (ARO), and the Knoebel Center for the Study of Healthy Aging (KIHA) at the University of Denver.
Background information on aerosols and bioaerosols
Most work in the Huffman Group is focused on the study of approximately micrometer-sized (10-6 m) biological aerosols (bioaerosols, e.g. fungal spores, bacteria, pollen). Such particles suspended in the atmosphere are critical to the life-cycles of many organisms and can have global impact by influencing hydrological cycle and climate as nuclei on which certain types of cloud droplets form. Below are links to a few good sources of information about aerosols and bioaerosols.
Good overview descriptions of atmospheric aerosols.
Overview articles about bioaerosols and their role in the Earth system: Fröhlich-Nowoisky et al. 2016, Després et al., 2012.
Page last updated: 02/21/2017.