Optical Test for Cancer

An extremely sensitive, yet simple optical method for detecting formaldehyde: The approach is based on multipass spectroscopy, which introduces a laser through a small hole in a mirror. The laser light then bounces back and forth between mirrors, creating interaction lengths with the sample that are tens or hundreds of times the length of the cell. (Source: M. Winkowski, U. Warsaw)

Researchers have developed an extremely sensitive, yet simple optical method for detecting formal­dehyde in a person’s breath. Because formal­dehyde is being studied as a potential biomarker for lung and breast cancer, the new method could one day lead to an inex­pensive and fast way to screen for cancer. “Measuring biomarkers in exhaled breath is noninvasive, painless and fast and could be used to screen for cancer even at very early disease stages, which is crucial for success­ful treatment,” said research team leader Mateusz Winkowski from the University of Warsaw in Poland. “The optical method we developed could make this type of measurement more practical and inex­pensive.”

Winkowski and Tadeusz Stacewicz show that their new optical sensing method based on multipass spectro­scopy can detect the presence of 1 molecule of formal­dehyde in a million air particles, or 1 part per million, even in the presence of gasses that can interfere with optical measurements. “Our dream is to one day build a table-top device that would be inexpensive and could be used for cancer screening in any medical consulting room,” said Winkowski. “During a basic medical exa­mination, the patient could blow into the device, and within a minute the doctor would know if the patient might need addi­tional conventional exami­nations.”

Spectro­scopy can be used to identify the chemical composition of a substance by measuring the color of light absorbed or emitted from a sample. A spectro­scopy approach known as multipass is useful for detecting low concen­trations of gas molecules because it increases the extent to which the light interacts with the sample. This setup uses an experi­mental cell with a mirror on each end. A laser introduced through a small hole in one mirror then bounces back and forth in the cell, creating interaction lengths tens or hundreds of times the length of the cell.

When trying to detect extremely low concen­trations, noise can be a problem with multipass spectro­scopy. This is because the multiple laser beams create a type of optical interference called fringe inter­ference that decreases sensi­tivity and makes it impossible to precisely determine the biomarker concen­tration. To reduce this optical inter­ference, the researchers developed a method called optical fringe quenching.

For the new optical fringe quenching technique, the researchers slightly change, or modulate, the emission of the laser over a range of wave­lengths and then average the light emitted from the sample over these wavelengths. This helps eli­minate the optical interference enough to allow detection of formal­dehyde. The researchers also selected a spectral range and sample pressure that helped reduce interference from other consti­tuents found in breath samples.

The researchers tested their new approach using cali­brated arti­ficial mixtures of formalde­hyde in air. Their results showed that the approach was more than sufficient to detect formalde­hyde in breath at levels that might indicate the presence of disease. “Our optical fringe quenching technique can be used to improve any optical system that uses a multipass cell,” said Winkowski. “It could also be useful for measuring formalde­hyde gas emitted from household materials or industrial sources to better understand its effects on human health.” Next, the researchers plan to test their analysis approach’s ability to measure ethane gas in breath. Study findings have sug­gested that ethane might also be used as a biomarker for cancer and other diseases. (Source: OSA)

Reference: M. Winkowski & T. Stacewicz: Optical detection of formaldehyde in air in the 3.6 µm range, Biomed. Opt. Exp. 11, 7019 (2020); DOI: 10.1364/BOE.405384

Link: Laser Spectroscopy, Faculty of Physics, University of Warsaw, Warsaw, Poland

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