A low-cost, highly-sensitive biological and chemical sensor to detect changes in the pH level of an environment has been developed by Cagri Savran, a study leader and an associate professor of mechanical engineering at Purdue University, along with Babak Ziaie, a Purdue University professor of electrical and computer engineering and biomedical engineering and a team of researchers.
"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," said Savran.
But this new sensor is inexpensive and easy to use while still remaining highly sensitive. The sensor, which is made of thin stripes of gelatinous hydrogel that expands and contracts based on the acidity of its environment, can expose information about different substances in liquid environments by measuring its pH.
Researchers in Ziaie's lab fabricated the hydrogel, while Savran's group led work in the design, development and testing of the diffraction-based sensor.
The diffraction-based sensor uses water-insoluble hydrogel to make a "diffraction grating," which is a series of raised stripes. These stripes are coated with gold, and expand and contract based on the pH level of the environments. The sensors can then analyze laser light, which reflects off of the cold coating. These reflections from the top of the stripes and the spaces in between them meddle with one another, which results in a diffraction pattern that changes based on the height of the stripes.
The diffraction patterns show small changes in movement of the hydrogel stripes when they react to the environment, which ultimately measures pH changes.
"By precise measurement of pH, the diffraction patterns can reveal a lot of information about the sample environment," said Savran. "This technology detects very small changes in the swelling of the diffraction grating, which makes them very sensitive."
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 showed the device's high sensitivity enables it to resolve changes smaller than one-1,000th on the pH scale, measuring swelling of only a few nanometers. A nanometer is about 50,000 times smaller than the finest sand grain.
"We know we can make them even more sensitive," said Savran. "By using different hydrogels, gratings responsive to stimuli other than pH can also be fabricated. 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."
The sensor's simple design could make it more practical than other sensors in development, he added.
New findings show the technology is highly sensitive and might be used in chemical and biological applications including environmental monitoring in waterways and glucose monitoring in blood.
"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," said Savran, Findings are detailed in a paper presented during the IEEE Sensors 2010 Conference in November and also published in the conference proceedings. The paper was written by postdoctoral researcher Chun-Li Chang, doctoral student Zhenwen Ding, Ziaie and Savran.