Government and academic research labs are advancing fluorescence-based spectroscopy for medical and military applications.
Fluorescence spectroscopy remains a powerful analytical technique for the detection and characterization of organic and inorganic compounds. Most of the power behind this methodology lies in its high sensitivity, but "also in its ability to adapt to a multitude of conditions and report on a wide range of effects, which has given it widespread usage," says Theodore Hazlett, director of the NIH-funded Laboratory for Fluorescence Dynamics (LFD) at the Univ. of Illinois, Urbana-Champaign.
Indeed, this versatility has allowed fluorescence spectroscopy to be employed in recent years in studies as diverse as identifying possible bacteria contamination on eggs to resolving the dynamics of human protein-protein interactions. It has also been increasingly used as a clinical technique in medicine.
Shedding light on disease
One of the more recent demonstrations of fluorescence spectroscopy's prowess in this arena has been at the Biomedical Engineering Dept., at the Univ. of Texas, Austin (UTA), where the application of interest has been in cervical cancer screening. "In the U.S. alone, more than $6 billion is spent every year in the evaluation and treatment of low-grade precursor lesions, and resources are wasted on the evaluation and treatment of lesions not likely to progress to cancer," says Rebecca Richards-Kortum, professor of biomedical engineering at UTA.
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The U.S. Army's ERDC Fluorescence Spectroscopy Lab is identifying fluorescent proteins associated with corals for extraction, sequencing and re-synthesis as synthetic fluorophores that they can incorporate into sensors and detectors. The image shows the fluorescence resonance energy transfer phenomenon between a high quantum yield fluorophore (a green fluorescent protein-like donor) and associated symbiotic algae (photo-pigment acceptors). |
In an effort to circumvent these costs, Richards-Kortum along with fellow researcher Michele Follen, are investigating the potential of a standard fiber-optic probe employing fluorescence spectroscopy to effectively scan cervical tissue for the presence of diseased cells.
According to UTA, "Cancerous cells interact differently with light than healthy cells and with the help of computer algorithms a real-time assessment of the light's interaction can result" and a determination of the patient's condition can be made.
"The new device doesn't require as much training and visual recognition skills as is required to perform a colposcopy (a secondary test administered when initial screening results are suspect)," says Follen. "It narrows the reporting time and is estimated to reduce the false positive rate by 40%."
Medical diagnostics is also an area of interest at the LFD using a variation of fluorescence spectroscopy. Fluorescence correlation spectroscopy (FCS) allows researchers to observe the dynamics of single molecules in real-time but at extremely low concentration levels. "We're investigating the application of FCS to turbid media for the rapid detection of low particle concentrations, with the practical aim to use it in scanning trace virus and bacteria presence in foods, water supplies, and biological fluids," says Hazlett. "In test cases of fluorescently tagged bacteria, we have been able to easily measure a concentration of 1,000 particles/mL in less than a minute."
These results have caught the eye of researchers at the Univ. of Kentucky's Chandler School of Aging, Lexington, who are interested in using this detection technique to estimate the concentration levels of amyloid aggregrates in bodily fluids—known to contribute to the formation of the plaque deposits associated with Alzheimer's disease.
Even with the applications noted, extending the use of fluorescence spectroscopy still has its challenges. "There is one encompassing issue that will always remain: fluorophore synthesis," says Hazlett. "Fluorescence spectroscopy relies on the brightness and characteristics of its fluorophores, (fluorescent molecules used to bind to the target species). Much of the creativity of the field is a result of the available probes."
Fluorophore solutions Designing and testing new fluoro-phores for military and commercial applications is one of the expressed purposes for the Fluorescence Spectroscopy and Microbiology Lab at Virginia Commonwealth Univ. (VCU), Alexandria. This lab is a spin-off from the Fluorescence Spectroscopy Lab at the U.S. Army Corps of Engineers, Engineering R&D Center (ERDC) and VCU's life sciences department.
Currently, the VCU lab is "adapting bio-inspired fluorescence by creating synthetic forms of proteins found in fluorescent organisms," says John Anderson, director of the facility. Among the organisms currently being studied are corals. "Our interest is not only in a synthetic fluorophore modeled on a natural one, but the mechanism in which the organism uses its fluorescence."
In addition to these efforts, the lab is also developing the use of fluorescence as a power source using robust, high yield fluorophores. "These fluorophores form a critical part of 'smart sensing' whereby a fluorescence emission is harnessed to power micro- and nanoscale detectors, involving chip-level sensing," says Anderson.
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In addition to applications in medicine, Univ. of Illinois researchers are using fluorescence spectroscopy for other life science studies. Shown is a fluorescence lifetime image of a parsnip plant leaf. The red area indicates regions where the plant is damaged and the photosynthesis is inoperative. (Image: Glen Redford) |
Researchers at the Univ. of Maryland Biotechnology (UMBI) Institute, Baltimore, are also experimenting with new fluorophores, but for a vastly different application. As recent as this past December, Chris Geddes, professor at UMBI and associate director of the Center for Fluorescence Spectroscopy, Baltimore, Md., along with his team, created a new series of highly sensitive fluorophores designed to be integrated into glucose sensing contact lenses.
"Despite intensive efforts, no method is currently available for the continuous, non-invasive monitoring of blood glucose," says Geddes. As a solution, the UMBI researchers doped off-the-shelf contact lenses with specially formulated boronic acid-based fluorophores that would show a spectral and/or color change in the presence of glucose within human tears, indicated on the surface of the lens.
"Our findings show that our approach is indeed suitable for the continuous monitoring of tear glucose levels in the range of 50 to 1000 µM, which typically track blood glucose levels, which are normally 5 to 10 times higher," says Ramachandrum Badugu, project researcher.
While human trials have yet to begin, the team remains optimistic about its potential use. "We envisage that multiple modes of sensing can be undertaken in the contact lens, such as radiometric, lifetime, and (visual) polarization-based glucose fluorescence sensing for both doped lenses and lenses containing unique sensing regions (spots)," says Badugu.
—Jeannette Mallozzi
Resources
Center for Fluorescence Spectroscopy, 410-706-3149,
http://cfs.umbi.umd.edu Laboratory for Fluorescence Dynamics, 217-244-5620,
http://lfd.uiuc.edu Univ. of Texas, Austin Biomedical Engineering, 512-471-3604,
http://www.bme.utexas.edu/ index.cfm Univ.of Maryland Biotechnology Institute, 410-385-6300,
www.umbi.umd.edu U.S. Army Fluorescence Spectroscopy Lab, 804-828-9709,
www.vcu.edu/remotesensing www.cimss.vt.edu