Pillalamarri Srikrishnarka
Dielectica traverses through the literature on this topic – and summarizes as they appear.
Key words: Diabetes mellitus, Glucose sensor
Chennai, India: Diabetes mellitus (DM), also known as diabetes is a metabolic disorder caused by the presence of high sugar in blood for prolonged duration. Globally ~ 8.8% i.e., 463 million people suffer from this disorder, classified into two major types, type – I and type – II. Type-I diabetes, also called as “juvenile diabetes” is a rare condition, where the pancreas cannot sufficiently secrete insulin and Type-II is the increased resistance to insulin generally caused due to poor lifestyle. Can lead to ketoacidosis, chronic kidney failure, cognitive impairment, nerve damage and stroke. Therefore regular monitoring of blood glucose level of a diabetic patient is advisable. However, pathological examination of blood sugar level by any patient is hectic. In recent days, glucose is detected by using glucometer, where a small drop of blood is placed on a strip and upon analysis would give the concentration of glucose (mg/dL). Even though, this is a widely used commercialized technology, it has its limitations as the patient needs to constantly monitor his/her blood glucose levels and frequent pricking of blood is uncomfortable. Thus there is a need for noninvasive technique for detection of blood glucose level.
Apart from blood, glucose is also present in tears, sweat and saliva. Monitoring these fluids is noninvasive and could provide some relief to the patients. In this regard, there has been substantial research [1] and few commercial products [2] have also been released which noninvasively monitors glucose. Need of constant sensor replacement and excessive cost are some of the major causes for these commercial products to reach the masses. Even though the amount of sweat or saliva one generates is sufficiently high, due to other components present, it could hamper the detection of glucose. Optical measurements of tear drops can detect the concentration of glucose, usually by fluorescence resonance energy transfer and also by surface plasmon resonance. [1] However, these two techniques require continuous tear generation and also laser, making them difficult for daily monitoring.
To address some of the major limitations and successfully monitor glucose concentrations noninvasively, Jeon et al., of Gwangju Institute of Science and Technology, Republic of Korea fabricated a smart contact lens. [3] This lens is comprised of nanoparticles of cerium oxide nanoparticles and glucose oxidase and polyethylene glycol complex embedded on the lens. As soon as glucose upon contact with the glucose oxidase, it oxidizes and produces hydrogen peroxide. This peroxide converts the Ce3+ to Ce4+ changing the colour of the lens in that process. These lenses are highly biocompatible and were tested for cytotoxicity using the human umbilical vein endothelial and human corneal epithelial cells. The testing rig is extremely simple, all it contains is a CCD camera, with a zoom lens of 0.45 X magnification. A photograph is initially captured of the lens, then by using simple image processing methodologies, the center of lens is tracked, the intensity of the image in red, blue and green channels were calculated and finally an average of all the three intensities estimates the glucose concentration. A schematic explaining the process is shown in the figure below.
Figure: Schematic illustration of colorimetric NECL and optical monitoring system. (a) NECL color was changed to yellow (colorless Ce3+ to yellow Ce4+) (b) A color CCD camera with a zoom lens for the demagnification (0.45×) record NECL surface color change (RGB). Reprinted with permission Copyright © 2021 American Chemical Society.
The system was tested both for rat and human tear, continuously monitored the glucose levels for diabetic rats when they were awake, sleeping due to inhalation and injected anesthesia. Every rats’ blood glucose levels was monitored prior to the experiment using the smart lens. They have observed almost 82 % and 71 % linear correlation between the blood and tear glucose concentration in case of humans and rats, respectively. Thus, this methodology is simple, could alleviate the discomfort and by developing a mobile phone application, it could potentially reach the masses.
References
[1] M. Chung, G. Fortunato, N. Radacsi, J. R. Soc. Interface, 2019, 16, 20190217.
[2] https://www.freestylelibre.co.uk/libre/
[3] H. J. Jeon et al., Nano Lett. 2021, 21, 8933–8940.