This custom-designed Android app displays test results on a smartphone screen. [David Baillot/UCSD Jacobs School of Engineering]
This custom-designed Android app displays test results on a smartphone screen. [David Baillot/UCSD Jacobs School of Engineering]

University of California, San Diego, researchers say they have developed a smartphone case and app that could make it easier for patients to record and track their blood glucose readings, whether they're at home or traveling.

Currently, checking blood sugar levels can be a hassle for people with diabetes, especially when they have to pack their glucose monitoring kits around with them every time they leave the house.

“Integrating blood glucose sensing into a smartphone would eliminate the need for patients to carry a separate device,” said Patrick Mercier, Ph.D., a professor of electrical and computer engineering at UC San Diego. “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 device, called GPhone, is a new proof-of-concept portable glucose sensing system developed by Dr. Mercier, nanoengineering professor Joseph Wang, Ph.D., and their colleagues at the UC San Diego Jacobs School of Engineering. Drs. Wang and Mercier are the director and co-director, respectively, of the Center for Wearable Sensors at UC San Diego. 

The team published its work (“Re-Usable Electrochemical Glucose Sensors Integrated into a Smartphone Platform”) in Biosensors and Bioelectronics. The article describes a new smartphone-based reusable glucose reusable meter.

GPhone has two main parts. One is a slim, 3D printed case that fits over a smartphone and has a permanent, reusable sensor on one corner. The second part consists of small, one-time use, enzyme-packed pellets that magnetically attach to the sensor. The pellets are housed inside a 3D printed stylus attached to the side of the smartphone case.

To run a test, the user would first take the stylus and dispense a pellet onto the sensor—this step activates the sensor. The user would then drop a blood sample on top. The sensor measures the blood glucose concentration, then wirelessly transmits the data via Bluetooth to a custom-designed Android app that displays the numbers on the smartphone screen. The test takes about 20 seconds. Afterwards, the used pellet is discarded, deactivating the sensor until the next test. The stylus holds enough pellets for 30 tests before it needs to be refilled. A printed circuit board enables the whole system to run off a smartphone battery. 

The pellets contain glucose oxidase, which reacts with glucose. This reaction generates an electrical signal that can be measured by the sensor's electrodes. The greater the signal, the higher the glucose concentration. The team tested the system on different solutions of known glucose concentrations. The results were accurate throughout multiple tests. 

A key innovation in this design is the reusable sensor, say the researchers. In previous glucose sensors developed by the team, the enzymes were permanently built in on top of the electrodes. The problem was that the enzymes wore out after several uses. The sensor would no longer work and had to be completely replaced. Keeping the enzymes in separate pellets resolved this issue. 

“Such a unique working principle allows the system to overcome challenges faced by previously reported reusable sensors, such as enzyme degradation, leaching, and hysteresis effects. Studies reveal that the enzyme loaded in the pellets are stable for up to 8 months at ambient conditions, and generate reproducible sensor signals,” write the investigators. “The work illustrates the significance of the pellet-based sensing system towards realizing a reusable, point-of-care sensor that snugly fits around a smartphone and which does not face issues usually common to reusable sensors. The versatility of this system allows it to be easily modified to detect other analytes for application in a wide range of healthcare, environmental and defense domains.”

The team envisions one day integrating glucose sensing directly into a smartphone rather than a case. Some next steps include testing on actual blood samples and minimizing sample volumes—the current prototype uses at least a dozen drops of sample per test, so researchers aim to cut that down to an amount that's normally extracted from a finger prick. They also plan to include a function in the app that send phone alerts reminding users to check their blood sugar.