New technique monitors blood sugar with light

Diabetes is a very common disease that, unfortunately, still has no cure. People with diabetes must regularly monitor their blood glucose levels (BGLs) and administer insulin to keep them under control. In almost all cases, BGL measurements involve drawing blood from the tip of the finger through a puncture. Since this procedure is painful, less invasive alternatives utilizing modern electronics are being actively explored worldwide.

So far, various methods of measuring BGL have been proposed. The use of infrared light is a case in point, and devices based on mid-infrared light have shown reasonable performance. However, the required sources, detectors and optical components are expensive and difficult to integrate into portable devices. Near infrared (NIR) light, in contrast, can be easily produced and detected using inexpensive components. Many smartphones and smartwatches already use NIR sensors to measure heart rate and blood oxygen levels. Unfortunately, glucose does not have unique absorption peaks in the NIR region and is therefore difficult to distinguish from other blood chemicals such as lipids and proteins.

To address this limitation, a research group led by Tomoya Nakazawa of Hamamatsu Photonics (Japan) recently developed a new methodology to estimate BGLs from NIR measurements. Their work, which could revolutionize non-invasive blood glucose monitoring, was published in Journal of Biomedical Optics.

The key contribution of this study is a new indicator of blood glucose levels that the research team obtained from basic types of NIR. Their approach begins with the extraction of oxyhemoglobin (HbO₂) and deoxyhemoglobin (Hb) signals from NIR measurements. Through the analysis of massive amounts of data for NIR measurements, the researchers realized that the phase delay (asynchrony) between the low-frequency and oscillatory components of HbO₂ and Hb signals are closely related to the degree of oxygen consumption during each cardiac cycle, thus serving as a gauge for metabolism.

This phase lag-based metabolic index, which has not been reported by other researchers, is a scientifically significant discovery.”

Tomoya Nakazawa, Hamamatsu Photonics

The team then sought to prove the relationship between this newly discovered metabolic marker and BGLs through a series of experiments. First, they used the NIR sensor in a commercial smartwatch by placing it over the finger of a healthy subject at rest. The subject then consumed different sugar and sugar-free drinks to induce changes in blood glucose. Similar experiments were conducted using a custom smartphone stand with high-brightness LEDs. The results were promising, as metabolic index changes closely matched fluctuations in blood glucose levels measured by a commercial continuous glucose monitor. This confirms that the phase lag between HbO₂ and Hb is indeed closely correlated with BGLs.

Clinical trials in diabetic subjects are pending to confirm the applicability of the metabolic index in a real-world setting. However, the researchers have high hopes for their innovative technique, as Mr. Nakazawa reports: “The proposed method can in principle be applied to existing smart devices with pulse oximetry function and is cheap, battery-saving and simple compared to other non-invasive blood glucose monitoring techniques. Thus, our approach could be a powerful tool for portable and accessible BGL monitoring devices in the future.”

Hopefully, these efforts will contribute to practical, non-invasive ways for people with diabetes to keep their BGLs under control, thereby minimizing the impact of their disease!