Ultrasound-modulated optical glucose sensing using a 1645 nm laser

Abstract

Regular and frequent blood glucose monitoring is vital in managing diabetes treatment plans and preventing severe complications. Because current invasive techniques impede patient compliance and are not infection-free, many noninvasive methods have been proposed. Among them, optical methods have drawn much attention for their rich optical contrast, but their resolution is degraded in deep tissue. Here, we present an ultrasound-modulated optical sensing (UoS) technique to noninvasively monitor glucose that uses an infrared laser (1645 nm) and a single-element focused ultrasound transducer. Focused ultrasound waves can acoustically localize diffused photons in scattering media, and thus optical contrast can be represented with much enhanced spatial resolution. to maximize the signal-to-noise ratio, we compared the modulation depths of UoS signals in both continuous and burst ultrasound transmission modes. finally, UoS measurements of various glucose concentrations are presented and compared with those acquired in phantoms with a conventional diffuse optical sensing method. The UOS measurements in a 20 mm thick tissue-mimicking phantom show 26.6% accuracy in terms of mean absolute relative difference (MARD), which indicates the great potential of the proposed technique as a noninvasive glucose sensor. Diabetes mellitus is a chronic metabolic disorder that causes high blood sugar (glucose) levels due to either insufficient production of insulin or inadequate cellular response to the produced insulin 1. Diabetes can lead to serious complications, such as cardiovascular disease, stroke, blindness, chronic renal failure, neuropathy, or even death 2-4. As of 2019, it is estimated that 463 million people are suffering from diabetes worldwide, and this population is projected to reach 700 million by 2045 5. In 2012, the total cost of diagnosed diabetes in the USA was estimated to be $245 billion, and in 2013 over five million people between 20-79 years of age were estimated to die from diabetes-associated causes worldwide 6,7. Although there is no known cure for the disease, diabetic patients can minimize complications through timely and constant care and treatment in conjunction with regular blood glucose monitoring. Current glucose sensors require either drawing a drop of blood by finger-pricking or inserting the sensor under the skin. The repetitive use of these invasive devices causes pain and can lead to infection, tissue damage, or reduced patient compliance. Accordingly, noninvasive glucose sensors have been increasingly sought in recent decades 8-12. Most noninvasive sensors are based on electromagnetic (EM) waves, especially within optical wavelengths, because these waves interact richly with various components of biological tissues. Raman spectroscopy, using near-infrared (NIR) and mid-infrared (MIR) illumination, detects the Raman shift from inelastic scattering by glucose molecules. It provides high specificity and is relatively robust to water and temperature changes, but requires a long collection time 13,14....

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