Non-Invasive Glucose Monitoring via Polarized Photoacoustic Sensing

Researchers from the Indian Institute of Science (IISc) Department of Instrumentation and Applied Physics (IAP) have developed a new method called photoacoustic sensing, which offers an alternative approach to measuring blood glucose levels.

Typically, blood glucose levels are measured using invasive techniques that involve inserting tiny needles into the skin. However, people with diabetes must check their blood sugar levels several times a day. This frequent needle use can be both inconvenient and increases the risk of infections.

The new method involves shining a laser beam onto biological tissue, which causes the tissue to absorb light and warm up slightly (less than 1 °C). Sensitive detectors capture the vibrations produced by the tissue's expansion and contraction as ultrasonic sound waves.

The sound waves released by the tissue's components and molecules form distinct "fingerprints," as they absorb different amounts of light at various wavelengths. This process does not harm the tissue sample under study.

In this investigation, the researchers used the method to quantify glucose concentration. They utilized polarized light, which oscillates in a single direction. Glucose, being a chiral molecule, rotates the light's oscillation orientation when it interacts with the polarized light. The team found that adjusting the orientation of the polarized light interacting with glucose in the solution changed the intensity of the released sound waves.

We do not actually know why the acoustic signal changes when we change the polarisation state. But we can establish a relationship between the glucose concentration and the intensity of the acoustic signal at a particular wavelength.

 Jaya Prakash, Assistant Professor and Study Corresponding Author, Department of Instrumentation and Applied Physics, Indian Institute of Science

The intensity of the acoustic signal corresponds to the rotation of the polarized light caused by glucose, which increases with its concentration. By analyzing the strength of the acoustic signal, the researchers were able to estimate the glucose content.

With near clinical accuracy, the researchers determined the glucose levels in animal tissue slices, water, and serum solutions. Additionally, they were able to precisely measure glucose concentration at different depths within the tissue.

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.

Swathi Padmanabhan, Ph.D. Student and Study First Author, Department of Instrumentation and Applied Physics, Indian Institute of Science

The researchers were able to obtain precise measurements at different tissue thicknesses because sound waves do not disperse significantly within the tissue.

Additionally, the scientists used the sensor setup to monitor a healthy participant's blood glucose levels before and after meals over a period of three days as part of a pilot study.

Finding the right setup to do this experiment was very challenging. 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.

Swathi Padmanabhan, Ph.D. Student and Study First Author, Department of Instrumentation and Applied Physics, Indian Institute of Science

By adjusting the wavelength of the light, the authors believe this method could potentially be applied to any chiral chemical.

During the investigation, the concentration of naproxen, a common medication for treating minor pain and inflammation, was also measured in an ethanol solution.

This technology has a wide range of potential applications in diagnostics and healthcare, as many commonly used medications are chiral.

Journal Reference:

Padmanabhan, S., et al. (2025) Deep tissue sensing of chiral molecules using polarization-enhanced photoacoustics. Science Advances. doi.org/10.1126/sciadv.ado8012.