Simple and Precise Hydrogel Sensor Could Be Used for Glucose Monitoring

Researchers at Purdue University (West Lafayette, IN) are developing a new type of biological and chemical sensor that has few moving parts and is highly sensitive, sturdy, and long-lasting. Capable of determining pH, the sensor could be used in biological applications, including glucose blood monitoring.

The sensor is based on a water-insoluble hydrogel that is formed into a series of raised stripes called a "diffraction grating." The stripes and the spaces between them are coated with gold. The sensors work by analyzing laser light reflecting off the gold coatings. Reflections from the stripes and spaces between them interfere with each other, creating a diffraction pattern that differs depending on the height of the stripes. These diffraction patterns indicate minute changes in the movement of the hydrogel stripes in response to the environment, in effect measuring changes in pH. The sensor detects pH by expanding and contracting depending on the acidity of the environment.

The sensor's simple design could make it more practical than other sensors in development, remarks Cagri Savran, an associate professor of mechanical engineering at Purdue. "Many sensors being developed today are brilliantly designed but are too expensive to produce, require highly skilled operators, and are not robust enough to be practical," he says. "As with any novel platform, more development is needed, but the detection principle behind this technology is so simple that it wouldn't be difficult to commercialize."

Savran is collaborating with another team of researchers led by Babak Ziaie, a Purdue professor of electrical and computer engineering and biomedical engineering. While Ziaie's lab fabricated the hydrogel, Savran's group designed, developed, and tested the sensor.

The pH of a liquid is recorded on a scale from 0 to 14, with 0 being the most acidic and 14 the most basic. Findings indicate that the device's high sensitivity enables it to resolve changes smaller than 1/1000 on the pH scale, measuring swelling of only a few nanometers. "By precise measurement of pH, the diffraction patterns can reveal a lot of information about the sample environment," Savran comments. "This technology detects very small changes in the swelling of the diffraction grating, which makes them very sensitive."

"We know we can make them [the sensors] even more sensitive," Savran says. "By using different hydrogels, gratings responsive to stimuli other than pH can also be fabricated."