Development of confocal X-ray fluorescence techniques for biological and archaeological applications
Date
2016-05-12
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Thesis
Degree Level
Doctoral
Abstract
X-ray fluorescence imaging (XFI) is a versatile tool for determining spatial distributions of elements or elemental species within a variety of samples. A newer XFI variant, confocal X-ray fluorescence imaging (CXFI), shows significant promise since confocal detection facilitates important advantages such as three-dimensionally resolved elemental investigation, preservation of sample integrity and higher sensitivity. Additionally, a readily available extension of CXFI, confocal X-ray absorption spectroscopy (CXAS), allows determination of elemental speciation within a specific localized volume element. To enable direct visualization of three-dimensional elemental distribution and speciation in intact biological samples without staining or thinning, this thesis aimed at developing CXFI and CXAS for biological and archaeological applications.
CXFI and CXAS technique development included installing and refining the polycapillary based setup at beamline 20ID-B, Advanced Photon Source (APS), USA, and verifying the feasibility of different configurations through select measurements. In addition, a novel X-ray detection focusing optic, the spoked channel array (SCA) recently developed at the Cornell High Energy Synchrotron Source (CHESS), USA, was implemented to provide superior spatial resolution.
CXFI and CXAS were used to study the following scientific problems:
a) Embryonic exposure to elevated selenium in zebrafish: The localization and chemical form of maternally transferred selenium were studied in an early developmental stage of life to understand the effect of exposure.
b) Highly localized Fe speciation within intact corrosion layer in antique stained glass: SCA derived CXAS was employed to determine iron speciation in an antique stained glass sample from 13th century Paderborn Cathedral, Germany to aid the study of cleaning methods used in restoration.
c) Differentiating diagenesis from biogenicity: Archaeological bone samples from the Royal Naval Hospital Cemetery (c. A.D. 1793-1822), Antigua were studied in an attempt to distinguish between diagenetic and biogenic lead uptake. Systematic comparisons of conventional XFI with polycapillary and SCA-based CXFI showed that lateral spatial resolution was remarkably improved with SCA optics.
This research facilitated incorporating CXFI and CXAS at beamline 20ID-B, APS and establishing SCA optics as a valuable addition to the confocal X-ray detection toolkit. These capabilities will be implemented at the BioXAS imaging beamline at the Canadian Light Source.
Description
Keywords
Synchrotron, X-ray fluorescence imaging, confocal X-ray fluorescence imaging, confocal X-ray absorption spectroscopy, polycapillary, spoked channel array, selenium, zebrafish, antique stained glass, corrosion layer, archaeological human bone, lead, diagenesis
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Geological Sciences
Program
Interdisciplinary Studies