Cassandra L. Fraser
Polymeric Metal Complexes. Metallobiomaterials for Medicine and Biotechnology. Bio-inspired and Sustainable Design. Responsive Nanoscale Assemblies.
Research in the Fraser Lab is concerned with materials chemistry—synthesis, properties, and applications, along with environmental, health and societal impacts. While developing routes to polymeric metal complexes—well-defined hybrid inorganic-organic materials inspired by metalloproteins, combining coordination chemistry and controlled polymerization—we made two important discoveries involving luminescent boron complexes. Difluoroboron b-diketonate dyes show intense fluorescence, 2-photon absorption, and environment sensitive emission. As we and others have reported, they also display unusual optical properties in the solid state.
Oxygen Sensing Boron Biomaterials
Difluoroboron dibenzoylmethane-poly(lactic acid) analogues exhibit both intense fluorescence and long-lived room temperature phosphorescence. When fabricated as nanoparticles, these simple, dual-emissive biomaterials serve as optical oxygen probes for biology and medicine, with impressive combined spatial and temporal resolution. Along with fundamental studies, the materials have been optimized with respect to fluorescence and phosphorescence emission colors, relative intensities, luminescence lifetimes, oxygen sensitivities, and fabrication. With collaborators, we developed a portable, cost-effective, laptop camera imaging system that, in conjunction with boron nanosensors, allows for dynamic, real-time, single or dual mode (ratiometric and/or lifetime) tissue oxygen imaging. We have demonstrated the utility of these materials for in vitro and in vivo optical oxygen imaging in cell, tumor, wound, vascular, brain, immunological, tissue engineering, and other contexts.
Mechanochromic Luminescence and Other Stimuli Responsive and Environment Sensitive Properties
Difluoroboron b-diketonate dyes also show surprising properties as molecular solids. For example, we showed that the difluoroboron complex of avobenzone, a simple sunscreen ingredient, has narrow bandwidth green, cyan, or blue emission depending on the solid form. Furthermore, the emission color changes when crystals are crushed or films are scratched or rubbed. Surprisingly, for thin films, the mechanochromic luminescence is reversible. For the avobenzone complex, regions where force is applied turn yellow but return to the original green-blue background color within minutes at room temperature or seconds with heating. The writing-fading process may be repeated many times. Emission colors, force responsiveness, and self-healing times may be tuned through molecular design, and self-erasing properties may be monitored with video camera imaging. These simple Scratch the Surface InksTM show promise as mechanical sensors and renewable inks for rewritable surfaces. They have even inspired creative works in music, art, and design. Other interesting properties of boron dyes, and in some cases even b-diketones absent difluoroboron, include solvatochromism, viscochromism, halochromism, aggregation induced emission, dye thickness and loading effects, and energy transfer in dye mixtures. Interestingly, some dyes are also thermally responsive and form supercooled liquids. Synthesizing new dyes, exploring their many fascinating properties, and tailoring materials for imaging and sensing in biology, medicine, and other contexts serves as the focus of our research.
Integrative Interdisciplinary Projects
Professor Fraser also has a great passion for envisioning and leading innovative interdisciplinary programs that integrate teaching, research, community engagement and creative pursuits. These projects are often inspired by materials, and environmental health and sustainability themes. They build bridges across STEM and non-STEM disciplines and engage students, faculty, and the community with thought leaders from across UVA and the globe. Examples include the UVA Page Barbour supported Transduction and Plastic/ity projects, the Carnegie Corporation funded Designing Matter Common Course, the NIH Global Health funded Metals in Medicine and the Environment, the Biomaterials Workshop, the Echols seminar Color: Across the Spectrum, and the Science, Careers and Society Forum. Professor Fraser often collaborates with artists and designers on exhibitions and performances (e.g. Chromogenic Materials, Agents of Architecture, UVA Music Technosonics Festival, UVA Art Bestiary Exchange Portfolio, Environmental Art Activism, and Time books). She also engages in design projects to establish new kinds of venues for conducting and displaying interdisciplinary work (e.g. WallSpace, Real World Chemistry Lab). New research is concerned with Anthrochemistry—chemistry of the Anthropocene, investigating the human impacts of chemistry through element, molecule, and material case studies via an interdisciplinary global systems chemistry approach. Of particular interest are ways that materials, their pathways, and processes, are mapped onto and into our bodies and intersect with our everyday lives, affecting health and wellbeing. Laws, policies, social and environmental justice, and ethics and responsibility are also considered. Creative interdisciplinary ways of communicating findings to both university and broader audiences are also of interest.
Luminescent Difluoroboron β-Diketonate PLA-PEG Nanoparticles. Kerr, C.; DeRosa, C. A.; Daly, M. L.; Zhang, H.; Palmer, G. M.; Fraser, C. L. Biomacromolecules 2017, 18, 551-561.
Oxygen Sensing Difluoroboron β-Diketonate Polylactide Materials with Tunable Dynamic Ranges for Wound Imaging. DeRosa, C. A.; Seaman, S. A.; Mathew, A. S.; Gorick, C. M.; Fan, Z.; Demas, J. N.; Peirce, S. M.; Fraser, C. L. ACS Sensors 2016, 1, 1366-1373.
Mechanochromic Luminescence and Aggregation Induced Emission of Dinaphthoylmethane β-Diketones and their Boronated Counterparts. Butler, T.; Morris, W. A.; Samonina-Kosicka, J.; Fraser, C. L. ACS Appl. Mater. Interfaces 2016, 8, 1242-1251.
Polymorphism and Reversible Mechanochromic Luminescence for Solid-State Difluoroboron Avobenzone. Zhang, G.; Lu, J.; Sabat, M.; Fraser, C. L. J. Am. Chem. Soc. 2010, 132, 2160-2010.
A Dual-Emissive Materials Design Concept Enables Tumour Hypoxia Imaging. Zhang, G.; Palmer, G. M.; Dewhirst, M. W.; Fraser, C. L. Nat. Mater. 2009, 8, 747-751.
Multi-Emissive Difluoroboron Dibenzoylmethane Polylactide Exhibiting Intense Fluorescence and Oxygen-Sensitive Room-Temperature Phosphorescence. Zhang, G.; Chen, J.; Payne, S. J.; Kooi, S. E.; Demas, J. N.; Fraser, C. L. J. Am. Chem. Soc. 2007, 129, 8942-8943.
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