I joined BioXAS project as a staff scientist in Januray 2012 and became the project manager for BioXAS in November 2015 until the project closure in April 2018. At present, I am the responsible scientist for the BioXAS sector and also the senior scientist for the BioXAS-Imaging beamline.
The BioXAS sector, which comprises three beamlines, was designed to support health and life sciences as well as environmental research. Two beamlines are dedicated to X-ray Absorption Spectroscopy and can provide scientists with information of the elements present in their specimens and also their chemical speciation. The speciation of an element is very important as it determines toxicity, tissue uptake and metabolism as well as risks associated with exposure.
The third beamline, BioXAS-Imaging, is dedicated to X-ray fluorescence imaging and can map metals and other elements in various specimens at three spatial resolution modes, starting from 150 micrometers and going down to a quarter of a micrometer (see Figure in the left panel).
For more information on these beamlines, please visit the BioXAS sector website.
POE houses the beamline optics (filters, mirrors, monochromators), which manipulates the beam so is ready for the experiments in the experimental hutch, where the samples are mounted.
The X-ray light from POE is transferred into the endstation. This is enclosure where the sample is mounted and the data is collected.
The beamline optics transfers the X-ray light (monochromatic) along the beamline and focuses the beam to the desired size in the experimental hutch where the specimen is mounted. The sample is either step or fly-scanned in the focused beam with a defined dwell time per pixel (pixel size is usually consistent with the beam size). The images of elements’ distribution in the scanned specimen are built by a computer from single pixels’ X-ray fluorescence spectra recorded by the X-ray detector.
The pictures show mercury (Hg) localization in the live zebrafish larva (Macro, 40 micrometer resolution) or in the thin sections of the zebrafish larvae (Micro - 3 micrometer resolution and Nano-250 nanometer resolution) that were acutely exposed to methylmercury in water (RT-retina, BR-brain, EL-eye lens). These images were collected at the Stanford Synchrotron Radiation Lightsource (Macro) and at the Advanced Photon Source (Micro and Nano). More details are available in the following publications Korbas 2008, Korbas 2012, Korbas 2013.
I have pioneered the application of synchrotron techniques, X-ray Absorption Spectroscopy (XAS) and X-ray Fluorescence Imaging (XFI), to toxicological studies using zebrafish as a model vertebrate system. The importance and novelty of this contribution in this area was recognized in 2008 with the publication of a paper describing this work, Localizing organomercury uptake and accumulation in zebrafish larvae at the tissue and cellular level, in the Proceedings of the National Academy of Sciences USA (Figure 1). This study revealed novel target tissues for methylmercury, the eye lens and the retina. The finding was striking as it suggested a possible cause, beyond brain damage, for vision problems reported in some people suffering from methylmercury poisoning. In a follow-up study (Korbas 2010) we discovered that the eye lens could act as a major sink for methylmercury ions circulating in the body. In another study, by using high resolution XFI (Figure 2), we identified the outer segments of both retinal and pineal photoreceptors as the preferential sites for methylmercury accumulation (Korbas 2013).
We also demonstrated dramatic tissue-specific differences in mercury uptake in developing zebrafish depending on the chemical form of mercury toxicant (Korbas 2012). Interestingly, the preferential uptake and accumulation of mercury in the eye could only be observed in methylmercury exposed fish but not in the inorganic mercury treated fish (Figure 3).
Dorsal (left) and lateral (right) views of 4.5 days post fertilization (dpf) living zebrafish larva after 24-hour treatment with waterborne 0.1 mM MeHg-L-Cysteine. The X-ray fluorescence imaging maps of mercury (Hg), zinc (Zn) and calcium (Ca) at 10 micrometer resolution (middle and bottom rows) are compared with their respective optical images (top row).
P, S, Ca, Zn, and Hg distributions in transverse sections of fish eyes from 5 dpf larva exposed for 48 h to 500 nM methylmercury chloride measured using X-ray fluorescence imaging. The measured (unst) section is paired with the adjacent section’s histological image (H&E) [eye lens (le), ganglion cell layer (gcl), inner plexiform layer (ipl), inner nuclear layer (inl), outer plexiform layer (opl), retinal pigmented epithelium (rpe), outer nuclear layer (onl), and photoreceptors outer (os) and inner segments (is)].
Mercury distributions in the olfactory epithelium (left), the brain and the eye (middle) and the gastrointestinal track (right) in 5 dpf zebrafish larvae exposed for 36 hours to waterborne 1000 nM of either mercuric chloride or methylmercury chloride.
The purpose of this study was to understand the fate of methylmercury in the human brain and the role of selenium in its detoxification.
We used X-ray Absorption Spectroscopy and X-ray Fluorescence Imaging to investigate the molecular nature of mercury and selenium in human brain tissue taken from five individuals with varying mercury exposure (two individuals with acute exposure to high levels of methylmercury, two individuals with a lifetime of high fish consumption, and one subject with minimal fish consumption and no known exposure). After high exposures to methylmercury, the cortical brain selenium levels were significantly elevated and the mercury was present in at least two chemically distinct species, an inert nano-particulate mercuric selenide and mobile mercuric bis-thiolate. In one case, substantial fraction of toxic methylmercury cysteineate species was also detected. After low chronic methylmercury exposures, the cortical selenium levels appeared undisturbed and the predominant forms of mercury were mercuric selenide and methylmercury cysteineate, both at much lower levels. Also, the remarkably invariant levels of organic selenium were observed in the studied samples.
Our results unequivocally confirmed that the demethylation process takes place in brain. Upon release from methylmercury, inorganic mercury is combined with selenium to produce mercuric selenide, thus clearly demonstrating a significant role of selenium in the detoxification process of methylmercury.
Please refer to the original manuscript published in ACS Chemical Neuroscience for more details and thorough discussion of the results.
As the X-ray energy is scanned across the respective X-ray absorption edge (e.g. Hg L3 edge for mercury), the absorbance pattern of the sample is measured either by utilizing the intensities of the beam before (I0) and after the sample (I) (as shown in the above figure) or by counting the respective X-ray fluorescence photons (e.g. Hg La1,2 for mercury) and normalizing these to I0 (not shown - X-ray fluorescence detector is usually positioned at 90 degrees to the beam). The approach depends on the concentration of the element of interest and the overall thickness of the sample.
The Hg L3 near edge spectrum of the sample is collected (experimental data) and compared to the Hg L3 spectra of the standards. Some prior knowledge of the sample is useful in choosing the standards for the speciation analysis. Here, we were able to reproduce the shape of the experimental spectrum with linear combination of three Hg standards: methylmercury cysteineate, nano-particulate mercuric selenide and mercuric bis-thiolate species.
We used X-ray Absorption Spectroscopy to investigate the speciation of mercury and selenium in human brain. Samples were examined from five individuals. Two of these individuals suffered from organic mercury poisoning. The others were the cases with average of above average fish consumption. You can find more details in Korbas 2010.
In both organic mercury poisoning cases, we detected the presence of nano-particulate form of mercuric selenide (nano-HgSe). For Case 1, we could not detect any organic mercury left in the brain meaning that the originally deposited methylmercury must have been transformed to inorganic mercury (mercuric biscysteineate and nano-HgSe). For Case 2, we could still detect some of the methylmercury in addition to the inorganic mercury species. This means that the transformation of organic mercury to inorganic mercury takes place in the brain but is not rapid and that selenium is involved in this process. You can find more results in Korbas 2010.
Here a few of the past studies that I was involved in. You can also find here a short description of my PhD and postdoctoral projects. For more details please explore my Publications or follow the links.
Mercury storage in the melano-macrophage aggregates
This was a collaborative research with Dr. Benjamin Barst (INRS-ETE, Universite du Quebec, at present University of Alaska). X-ray fluorescence imaging was used to detect mercury and other elements in liver sections of yelloweye rockfish and correlate deposition of mercury with melano-macrophage aggregate areas (Figure 1). These melano‐macrophage aggregates are composed of specialized cells of the innate immune system of fish and are considered a general biomarker for contaminant toxicity. The preferential accumulation of mercury in these macrophages, as compared with the surrounding hepatocytes, indicated their potential role in mercury detoxification and strorage.
Methylmercury accumulation in fruit fly larvae
In this collaborative research (with Dr. Matthew Rand and his group from University of Rochester), X-ray fluorescence imaging was used to identify the tissues with the highest mercury levels in methylmercury-exposed fruit fly larvae in order to understand the role of MRP (multidrug resistance-like protein) in moderating developmental susceptibility to methylmercury (Figure 2).
Novel iron binding motif in the iron-sulfur cluster-free hydrogenase (Hmd)
My postodoctoral training at the European Molecular Biology Laboratory in Hamburg, Germany, was focused on applying X-ray Absorption Spectroscopy in structural biology. One of the studies I was involved in was to reveal the structure and function of the iron centre in the iron site in the iron‐sulfur‐cluster free hydrogenase, an enzyme catalyzing the reversible oxidation of molecular hydrogen (Figure 3).
Gallium accumulation in bone tissue
This was the main focus of my PhD work. I used X‐ray absorption spectroscopy and micro‐X‐ray diffraction to determine the effects of gallium nitrate, a drug used in cancer patients, on bone tissue mineralization (Figure 4). The research was done using an in vitro model of bone formation. The bone marrow stromal cells were harvested from the femur bones of 8-week old male Wistar rats and cultured in the presence of dexametathasone, L-ascorbic acid and beta-glycerophosphate in order to induce their differentiation into osteoblasts and formation of bone tissue. Part of this project was done during my one year Marie Curie Training Fellowship at the European Molecular Biology Laboratory (EMBL) in Hamburg and using the EMBL and Hasylab beamlines in Hamburg.
Quantitative X-ray fluorescence images of mercury (Hg), selenium (Se), zinc (Zn) and iron (Fe) in the yelloweye rockfish liver section.
Distribution of mercury (Hg) versus other elements in larval central nervous system (CNS). (A) X-ray fluorescence image of Hg in the anterior region of the larva highlighting the CNS. (B) Immunostaining for the Elav neural specific antigen (red) shows labeling of the cellular cortical regions of the brain (Br) and ventral nerve cord (VNC). (C–D) Distribution of iron (Fe) and calcium (Ca) in the neuropil and cortex.
Structural models (deduced from X-ray Absorption Spectroscopy) of the iron site in Hmd holoenzyme andiron-containing Hmd cofactor derived by XAS. (A) active Hmd from M. marburgensis (mHmd); (B) CO-inhibited mHmd; (C) KCN-inhibited mHmd; (D) reconstituted active Hmd from M. jannaschii (jHmd wild type). (E) reconstituted active jHmd C10A or C250A mutants; (F) iron-containing Hmd cofactor.
Photo of the rat bone marrow stromal cell culture (bone nodule-left, cell culture chamber insert with mineralized bone nodules in white - middle).
The Ga K-edge k 3-weighted EXAFS spectra of the Ga-doped hydroxyapatite (Ga-HAP), amorphous calcium phosphate (Ga-ACP) and brushite (Ga-DCPD) in comparison with the Ga-exposed cell culture mineral spectrum (right panel).
I love sharing my enthusiasm for science and research by engaging in various outreach activities. I especially enjoy working with school groups and introducing young students to the power and potential of science, technology, engineering and mathematics (STEM) fields.
Students on the Beamlines
While at the Canadian Light Source (CLS), I was involved as a science mentor in the Students on the Beamlines program coordinated by CLS Education Team (Tracy Walker, Anna-Maria Boechler, Rob Blyth and David Muir). Participation in this program, provides high school students with an opportunity to experience firsthand the research process using Canada’s only synchrotron. The unique aspect of this program is that students take the lead in a project by researching the problem, planning appropriate experiments, preparing samples, collecting data and finally presenting their results in a poster form, as well as seminars at CLS and in their home communities The role of mentors is to help them to develop their research using the synchrotron techniques and support them during data collection and analysis.
This program not only benefits the students. Helping these budding researchers, and seeing their genuine interest in solving a problem are a source of inspiration for me and a reminder why I chose science the first place.
Teachers’ Workshops
I was a regular contributor to this annual event at the Canadian Light Source since 2012. My presentations were focused on exploring two synchrotron techniques, X-ray Absorption Spectroscopy and X-ray Fluorescence Imaging, and the benefits of applying these in toxicological studies. You can learn more about these techniques and my research in the Work section.
If you are a science educator interested in learning about Canada’s only synchrotron making connections to science curriculum, please visit the professional development section on the CLS Education website.
Health & Sciences Academy
In 2018, 2019 and 2021, I worked with Mrs. Andrea Regier, a science teacher at Bishop James Mahoney (BJM) Hight School in Saskatoon, who leads the Health & Sciences Academy at BJM High School. This is a unique program in which students can engage in health and life sciences through specialized classes and hands-on learning. You can read more about the Health & Sciences academy here. I talked to the students about mercury toxicity and my own research using the synchrotron. It was a great opportunity to connect with the students and share my knowledge and passion for science. I also learned lots from their questions as it is indeed true that “by teaching, we learn” (docendo discimus).
The Students on the Beamlines (SotB) team from Appleby College (2013) in front of Canadian Light Source. The team investigated the effects of the insecticide Malathion on Eremosphaera viridis algae on the mid-IR beamline at the CLS (2013).
Data collection at the mid-IR beamline (CLS) with the high school students from Appleby College (Oakville, Ontario) researching the effects of the insecticide Malathion on Eremosphaera viridis algae (2013).
The students from Bishop Carroll High School (Calgary, Alberta) during sample preparation at the IDEAS beamline. They were investigating the airborne transmission of peanut proteins and also researching selenium in nuts and supplements (2014).
The SotB team (2015) from Bernard Constant Community School (James Smith Cree Nation community, Saskatchewan).
Tour of the BioXAS beamlines (2015) with the students from Bernard Constant Community School (James Smith Cree Nation community, Saskatchewan). The visit to CLS was coordinated through Nipiy Network and allowed the students to perform measurements at the BioXAS-Side beamline.
Assisting a student from Bernard Constant Community School getting the samples ready for the measurements at the BioXAS-Side beamline (2015).
The SotB team from Evan Hardy Collegiate (Saskatoon, Saskatchewan) used both IDEAS and BioXAS-Main beamlines (2016) to investigate binding of mercury and selenium to the polysulfide polymers synthesized and kindly provided to the students by Dr. Justin Chalker from Flinders University (Adelaide, Australia).
Setting up an X-ray absorption spectroscopy (XAS) scan at the BioXAS-Main beamline (2016) with a student from Evan Hardy Collegiate (Saskatoon, Saskatchewan).
Discussing XAS experiments with SotB group from Evan Hardy Collegiate (Saskatoon, Saskatchewan) in 2016.
The SotB team (2016) from Uxbridge Secondary School (Uxbridge, Ontario). The students investigated the effects of copper (II) nitrate on Daphnia magna health.
Tour of the BioXAS sector (2016) with the students from Uxbridge Secondary School (Uxbridge, Ontario).
Tour of the experimental hutch at the BioXAS-Main beamline with the Uxbridge Secondary School SotB group (2016).
Demonstrating the components of the BioXAS-Main endstation for the Uxbridge Secondary School students (2016).
Observing live Daphnia magna using the stereo microscope at the BioXAS-Imaging beamline with the Uxbridge Secondary School students (2016).
The SotB team (2018) from Sentinel Secondary School (West Vancouver, British Columbia). The students investigated the accumulation of copper in Fucus Gardneri seaweed using X-ray fluorescence imaging at the BioXAS-Imaging beamline (CLS).
The SotB team from Sentinel Secondary School (West Vancouver, British Columbia) taking data at the BioXAS-Imaging beamline.
Mounting seaweed samples in the BioXAS-Imaging experimental area (2018) with the students from Sentinel Secondary School (West Vancouver, British Columbia).
Explaining the BioXAS-Imaging endstation setup to the SotB group from Halifax Grammar School (2020). The students were investigating the elemental composition and the presence of metal contaminants in blue mussels’ tissues.
During the COVID-19 pandemic, the SotB groups could not attend their beamtimes in person. In 2022, I mentored a group of students from the Carlton Comprehensive High school from Prince Albert (SK). The students investigated the accumulation of metals in fish ear stones called otoliths. With the assistance of the the beamline staff, they collected their data remotely at the BioXAS-Imaging beamline. Here, I'm providing the online tutorial on X-ray fluorescence microscopy data analysis with the PyMca software. Despite not being able to participate in person in data collection, the students were still able to experience the synchrotron data collection and analysis, and to present their data to the Canadian Light Source community.
St. Thomas More Collegiate (Burnaby, BC) students came to the BioXAS-Imaging beamline in November 2023 to study accumulation of metals in fish eye lenses.
The disposition of mercury in the central and peripheral nervous systems, including the sensory organs such as the eye and the ear is rarely investigated; yet, there is increasing evidence of the detrimental effects of organic and inorganic Hg species on animal behavioral patterns and sensory responses, which could stem from mecury accumulation in both the nervous system and sensory structures.
Recently, together with a group of mercury researchers, we have published an extensive review on the mercury neuronal and sensory toxicity in fish. You can read it in Biochimica et Biophysica Acta (BBA) - General Subjects.
Using the synchrotron techniques, I am also further exploring the disposition of mercury in the mammalian peripheral nervous system.
H&E stained section of mammalian retina
