This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Researchers have developed a compact, handheld mid-infrared imaging spectrometer that can produce high-resolution chemical maps of a sample without using stains or labels. With further development, the handheld device might provide a portable and easy-to-use way to map the molecular makeup of tissues and other samples.
"Ultimately, this technology could make it possible to assess tissue during cancer surgery," said research team leader Rohith Reddy of the University of Houston. "After removing a suspected tumor, a surgeon could scan the freshly excised tissue to help determine whether it is malignant or whether cancer cells remain at the surgical margin. This complementary information would be available while the patient is still in the operating room instead of having to wait for results from laboratory testing." In Optica, the researchers describe how they transformed a photothermal mid-infrared spectroscopic imaging (MIRSI) system, normally a benchtop instrument occupying more than 9 square feet (0.8 square meters), into a handheld probe measuring 8 by 8 inches (20 by 20 centimeters).
The probe holds the full optical head and connects by a flexible fiber tether to a compact base unit housing the lasers and control electronics. In side-by-side tests, it delivered image quality and chemical detail comparable to a state-of-the-art benchtop MIRSI system. "Although the current platform is still a research prototype, it establishes a technical foundation for field-deployable, label-free chemical imaging," said Reddy.
"A handheld MIRSI device could be useful for clinical diagnosis, polymer manufacturing, pharmaceutical quality control, forensic analysis or any application where chemical composition must be measured outside a specialized laboratory." Photothermal mid-infrared spectroscopic imaging systems map the molecular composition of tissue or other samples, showing where different biochemical components are located. Because molecules absorb mid-infrared light at wavelengths determined by their molecular bonds, they produce characteristic spectra that can be used to distinguish proteins, lipids, nucleic acids and other components. Unlike conventional infrared imaging, which typically uses infrared light itself to form an image, photothermal imaging detects tiny heat-induced changes caused by infrared absorption.
Although this approach produces high-resolution chemical images, it typically requires a large laboratory-based instrument. "Our initial goal was to determine whether a compact design could preserve the laboratory system's essential capabilities," said Reddy. "The resulting platform was even closer in size and form to a clinically deployable device than we initially expected, providing a strong foundation for future clinical translation." Miniaturizing a photothermal MIRSI instrument is especially challenging because it requires visible and mid-infrared light to be focused onto the same point.
These two wavelength ranges generally require different optical materials because materials that work well for visible light often absorb mid-infrared light, while those that work for mid-infrared light can introduce dispersion and other wavelength-dependent distortions that degrade the signal. To create a compact and flexible MIRSI system, the researchers used chalcogenide optical fibers to deliver mid-infrared light directly from the laser, eliminating bulky free-space optics. They also replaced traditional lenses with mirrors.
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