Painless Technique Measures Glucose Concentrations in Solution and Tissue Via Sound Waves

Blood glucose levels are traditionally measured using invasive methods that require pricking the skin with small needles. However, for individuals with diabetes, frequent testing throughout the day becomes necessary, making repeated needle use both inconvenient and potentially increasing the risk of infection. Now, a new study has presented a novel, non-invasive approach using photoacoustic sensing as an alternative solution.

Developed by researchers at the Indian Institute of Science (IISc, Bengaluru, India), the approach using photoacoustic sensing involves shining a laser beam onto biological tissue. When the tissue absorbs the light, it heats up slightly (less than 1°C), causing it to expand and contract. These slight vibrations generate ultrasonic sound waves that are detected by sensitive equipment. The key advantage of this method is that it does not cause any damage to the tissue being examined. In this study, published in Science Advances, the researchers applied this technique to measure the concentration of glucose, a single molecule.

The researchers used polarized light, which oscillates in one specific direction, to interact with glucose. Polarized light, like that used in sunglasses to block glare, can be affected by the chiral nature of glucose. A chiral molecule has an asymmetrical structure that causes polarized light to rotate its orientation when it interacts with the molecule. The team found that the intensity of the emitted sound waves changed when the orientation of the polarized light interacting with glucose was altered. The glucose molecules caused the light to rotate, and the degree of rotation increased with the glucose concentration. By measuring the strength of the acoustic signal, the researchers were able to determine the glucose concentration.

The team successfully measured glucose concentrations in water, serum solutions, and slices of animal tissue with near clinical accuracy. They were also able to measure glucose levels at varying depths within the tissue, thanks to the minimal scattering of sound waves in the tissue, which allows for accurate readings. In a pilot study, the researchers used the setup to track the blood glucose concentrations of a healthy individual before and after meals over three days. The researchers believe this technique could be adapted for use with any chiral molecule by adjusting the wavelength of light. In their study, they also measured the concentration of naproxen, a common medication used for mild pain and inflammation, in an ethanol solution. Given that many widely used drugs are chiral, this technique holds significant potential for broader applications in healthcare and diagnostics.

“If we know the speed of sound in this tissue, we can use the time series data to map our acoustic signals to the depth at which they are coming from,” said Swathi Padmanabhan, PhD student and first author of the paper. “Currently, the laser source we use has to generate very small nanosecond pulses, so it is expensive and bulky. We need to make it more compact to put it to clinical use. My lab mates have already started work on this.”

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