A team of researchers at the University of Maryland (College Park, MD) and Harvard Medical School (Cambridge, MA) has developed a novel spectroscopy configuration that can obtain a biological sample's entire Brillouin spectrum in one shot, saving time and allowing for noninvasive biological characterization in, say, potentially cancerous tumors.
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At a microscopic level, every material contains spontaneous sound waves (acoustic phonons) that have properties dependent on the material's mechanical properties. When light interacts with these acoustic phonons, it scatters and acquires a frequency shift related to the material's elastic modulus, a characteristic measure of its ability to resist deformation and stress.
A technique known as Brillouin spectroscopy works by measuring this frequency shift, and has been an effective tool for noninvasively examining materials for several decades. The technique, however, involves scanning interferometers, which are low-throughput and result in long data acquisition times. So, to bring this method to biological samples, the research team developed a new virtually imaged phased array (VIPA)-based Brillouin spectrometer.
The research team has been developing the VIPA-based Brillouin spectrometer for a long time, according to Giuliano Scarcelli, an assistant professor in the Fischell Department of Bioengineering at the University of Maryland. In this most-recent work, though, they added a multi-pass low-finesse Fabry-Perot interferometer, which works as a tunable and narrowband filter, Scarcelli says.
|Intralipid solutions of 0%, 0.01%, 0.1%, 1%, 10% and 20% concentrations--the new three-stage spectrometer can suppress the background light of up to a 5% Intralipid solution with a total loss of over 90% (top), and the signal-to-background ratio of Brillouin spectra for the concentrations (bottom). (Image credit: G. Scarcelli/UMD)|
While past development of VIPA-based spectrometers allowed the researchers to collect the entire Brillouin spectrum in a single shot, saving processing time and power, the design could only interrogate transparent materials such as ocular tissue or cells because turbid media generate too much unwanted light noise for the spectrometer to handle. By adding a triple-pass Fabry-Perot filter, the researchers were able to increase the spectrometer's ability to suppress such unwanted light component by more than tenfold, allowing them to measure background-free spectra up to 100 µm deep within a sample of chicken tissue.
Future work for Scarcelli and his colleagues includes improving Brillouin technology to measure spectra faster, with greater sensitivity and at higher spatial resolution, as well as expanding characterization to include tumors, atherosclerotic plaques, and brain tissue.
Full details of the work appear in the journal Applied Physics Letters; for more information, please visit http://dx.doi.org/10.1063/1.4948353.