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Blood Glucose Monitor Built Into Smartphone Case

GPhone prototype

GPhone prototype (Jacobs School of Engineering, University of California in San Diego)

8 December 2017. Engineers at University of California in San Diego designed a case that fits over a smartphone with an integrated sensor, which in lab tests accurately measures blood glucose levels. A team led by engineering professors Patrick Mercier and Joseph Wang describe the device and its proof-of-concept tests in a recent issue of the journal Biosensors and Bioelectronics (paid subscription required).

The UC-San Diego team seeks to take advantage of the computing power widely available to people through their mobile devices, to make it easier for persons with diabetes to measure their blood sugar levels using a smartphone. Diabetes is a chronic disorder where the pancreas does not create enough insulin to process the sugar glucose that flows into the blood stream and cells for energy in the body. In type 2 diabetes, which accounts for some 90 percent of all diabetes cases, the pancreas produces some but not enough insulin, or the body cannot process insulin.

Individuals with diabetes need to closely monitor their blood glucose levels, with many glucose testing meters on the market. But a glucose meter is another separate device that people with diabetes need to remember to take with them during the day. Thus Mercier, Wang, and colleagues want to use the computing power in a smartphone to keep track blood glucose levels. “Integrating blood glucose sensing into a smartphone would eliminate the need for patients to carry a separate device,” says Mercier in a university statement. “An added benefit is the ability to autonomously store, process and send blood glucose readings from the phone to a care provider or cloud service.”

The researchers call their device the GPhone, with a 3-D printed case that fits over the phone. In one corner of the case is a sensor with a receptacle to capture a blood sample for analysis. Attached to the case is a stylus containing carbon pellets, dispensed one at a time that attach magnetically to the sensor. The pellets are made of carbon and the enzyme glucose oxidase that reacts in the presence of glucose to form glucolactone. When exposed to oxygen in the air, glucolactone converts oxygen to hydrogen peroxide, which sensors in glucose meters and the GPhone can measure. Thus, the higher the glucose concentration in blood, the more hydrogen peroxide produced.

The enzyme-loaded pellets are used only one time, then discarded. These single-use pellets overcome a problem with reusable sensors in some glucose-monitoring devices, where the enzyme degrades or leaks out, requiring that the sensor or the entire device be replaced. The authors report the GPhone’s pellets are stable for 8 months. Each test takes about 20 seconds. A companion app displays results of each test on the smartphone screen.

In the journal paper, the team evaluated the working features of the system, to prove its concept. The researchers used blood samples with known glucose concentrations that they matched against readings from the sensor, and they report the GPhone gives accurate readings each time.

The prototype developed for testing still needs refinements, say the authors. The GPhone requires about a dozen drops of blood to read glucose levels, and the team wants to reduce that quantity to a single drop like that used in most of today’s glucose monitors. The researchers also are working on a system fully integrated into a smartphone, and not requiring the added case. But the authors say the technology can be extended to other types of substance monitoring. “This system is versatile,” notes Wang, “and can be easily modified to detect other substances for use in health care, environmental and defense applications.”

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