We perceive the world around us through visible light—the wavelength of electromagnetic radiation detectable by the human eye. However, visible light is just a tiny sliver in the entire spectrum of electromagnetic radiation, which begs the question: is there more to physical objects than what meets the eye?
There is, says Leonid Krivitsky, project lead for quantum technologies at A*STAR’s Institute of Materials Research and Engineering (IMRE). For example, we can extract information about the chemical composition of biological specimens based on how they selectively absorb infrared (IR) light using a technique called hyperspectral microscopy.
“Measurement of microscopic chemical content is essential for many tasks in bio-imaging, pharmaceutic industry, food quality control and other areas,” explained Krivitsky, “For example, it can be used to differentiate between malignant and healthy tissues in clinical studies.”
The problem, however, is that detecting IR requires complex and expensive specialized equipment, hindering both its widespread adoption and its application potential.
To overcome these challenges, Krivitsky’s team and collaborators from Gianluca Grenci’s group from the Mechanobiology Institute at the National University of Singapore created a workaround—a method for performing IR spectroscopy using simple, off-the-shelf components built for detecting visible light.
In this technique, two light beams are generated: the IR beam that interacts with the sample, and the visible beam that acts as a reference. The researchers exploited a phenomenon called induced coherence, or the transfer of information between beams of light having different wavelengths. “We used this smart trick to transfer the information about the chemical properties of the sample, captured by the IR beam, to the visible beam, which is very easy to detect,” Krivitsky said.
Next, the scientists validated their technique using a photoresist, a medium that changes properties after exposure to ultraviolet light. These changes can only be detected using IR spectroscopy. The team successfully demonstrated the capabilities of their imaging technique, which saw them achieving impressive lateral resolutions of around 17 microns, about twice the width of a red blood cell.
Importantly, with its wide field of view, quick readout and minimal heat delivered to the sample, this methodology paves the way for more exciting imaging opportunities, such as the study of live cells.
As next steps, Krivitsky and colleagues aim to refine the technique’s spectral resolution and measurement speed by leveraging frequency combs, which are laser sources that emit light at discrete, equally spaced frequencies.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering (IMRE).