New technique helps to image biological samples at the microscopic level

Researchers have developed a spectroscopic microscope to allow optical measurements of molecular conformations and orientations in biological samples. The new measurement technique allows researchers to image biological samples at the microscopic level faster and with more precision.

The new instrument is based on the discrete frequency infrared spectroscopic imaging technique developed by researchers at the Beckman Institute for Advanced Science and Technology at the University of Illinois at Urbana-Champaign.

This project aims to bring the study of molecular chirality into the microscopic field. “

Rohit Bhargava, Professor, Bioengineering, Director, Cancer Center, Illinois

Molecular chirality refers to the spatial orientation of atoms in molecules or multimolecular assemblies. In biological systems, a molecule can elicit a cellular response, while its mirror image can be inactive or even toxic. While vibrational circular dichroism can be used to help determine the chemical structure and orientation of a molecule, VCD measurements are time consuming and previously could not be used to image complex biological systems or tissue samples. solid.

The article “Simultaneous vibrational circular dichroism measurements with infrared spectroscopic imaging” was published in Analytical Chemistry and featured on the cover.

The new infrared microscope makes it possible to imaging the chirality of biomolecules by speeding up both the acquisition time and improving the signal-to-noise ratio of traditional VCD techniques.

“When you send light into a microscope from a spectrometer, you’re essentially throwing out a lot of it,” Bhargava said. “For VCD measurements, you also need to send it through a photoelastic modulator, which changes the polarization of the light to the left or right. At this point, you don’t have much light left, which means you have to average your signal over a long period of time to see only one pixel in an image. “

The Chemical and Structural Imaging Laboratory, led by Bhargava, performed rapid and simultaneous infrared and VCD measurements using the frame of their high performance discrete frequency infrared imaging microscope. Instead of using a traditional thermal light source, the instrument is built around a quantum cascade laser.

“The laser source was the driving force behind the whole design,” said Yamuna Phal, a graduate student in electrical and computer engineering. “The QCL source has a higher power, which means we can acquire faster measurements. Previously, you could only perform VCD on liquid samples, but we can also image solid tissue. been attempted before because it takes a long time to acquire VCD signals. in the first place. “

Kevin Yeh, a postdoctoral research associate, who co-led the development of the microscope, said other applications could arise from the microscope built for this project. “We initially envisioned the discrete frequency infrared microscope as a platform on which other techniques could be built,” Yeh said. “We have solved one of these extensions, which is VCD, but we could consider many more.”

While the applications of this technique may span the biological sciences, the work itself is testament to the strength of interdisciplinary science. “This project was only possible by bringing together the thoughts from different fields,” Bhargava said. “It’s a chemistry problem solved by a physics-based design, implemented by an electrical engineering student. It’s in our DNA at Beckman to take this kind of approach to problem solving.