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Case biomedical engineers develop first sliver-sized sensor to monitor glucose levels in diabetics

Case Western Reserve University : 28 January, 2007  (Technical Article)
It's a good thing that the son of Miklos Gratzl, a Case Western Reserve University biomedical engineer, got a splinter in his finger one day, at least for the sake of science.
With apologies to his son, instead of an 'Ouch!' moment, for Gratzl it was more of an 'A-ha!' moment.

As he was removing it from his son's finger, the splinter gave him an idea: Since it showed no open wound in the skin, he thought to himself that a sensor like a sliver would be great for all kinds of biomedical applications since the skin healed very quickly above it and after that no track infection can occur.

The associate professor of biomedical engineering and researcher at the Case School of Engineering has developed for the first time a 'sliver-sensor', a fully functional, minimally invasive, microscopic new monitor that can be placed just under the skin and seen with the naked eye for very accurate, continuous examination of glucose for diabetics and other bodily fluid levels with the help of simple color changes.

Gratzl and co-principal investigator Koji Tohda, a biomedical engineering researcher at Case, believe the implications for improving the quality of life of diabetics would be substantial.

'Many diabetics could greatly benefit from this technology, freeing them from having to take samples from their fingers several times a day to monitor blood sugar levels,' Gratzl said. 'The monitor could also help doctors with close monitoring of electrolytes, metabolites and other vital biochemicals in the body, primarily those of critically ill patients.'

Gratzl and Tohda's research may also benefit our future astronauts. The research is being funded by NASA and the John Glenn Biomedical Engineering Consortium at NASA Glenn Research Center, and partially by Vision Sensors LLC, a Cleveland-based startup.

Astronauts face the possibility of becoming ill while in space. Accidents may also happen. In such cases doctors on Earth have to make a diagnosis for a distance of several thousand miles. With this new approach, monitoring such vital markers as ions and metabolites in the interstitial fluid may make it easier and quicker to decide about the best intervention and therapy with a continuous monitor already in place. To date, no such continuous, minimally invasive monitor for ions and metabolites has been available.

Colors in the tiny sensor, which is one to two millimeters long and 100 to 200 micrometers wide, gradually change from orange (low glucose levels) to green and then to dark blue as levels increase. A deep, darker blue signifies the highest glucose level that can occur in diabetics.

Tohda's expertise in the area of optode technology helped to point the researchers in the direction of using color changing molecules to detect ionic levels as they vary due to variations in glucose. According to Gratzl, this approach is much more modern and powerful technology than the traditional color dyes. So Tohda suggested they create a sliver sensor that would generate color change instead of an electrical current.

'We also thought that color can be seen better from the outside if the sliver is not too deep, and if it gets distorted by the skin this can be corrected by using a white spot inside the sensor that does not change color,' Gratzl said.

The sensor, smaller than the tip of a pencil, penetrates the skin easily and painlessly so that users could insert or reinsert it themselves when needed and can be operational at least for several days at a time. It can be monitored by eyesight and by electronic telemetry using a watchlike device worn by the person for data processing.

Sensing itself does not require a battery, or the collection of blood samples, and needs very little energy if a watchlike signal processor is used. With no wires across the skin, there is no deterioration of the skin surface or other areas inside the skin and no danger of track infection. The device also is advantageous because no electrical currents are going through the body.

Gratzl says lab testing and in vivo testing in laboratory animals of the sensor has been going well.

'So far, the sensor is performing beyond expectation in preliminary laboratory tests,' Gratzl said. 'Over the years, there has been a lack of good, quality devices for diabetics to monitor glucose - something they must do every day of their lives - that are reliable, relatively low-cost and minimally invasive.'

Gratzl says the sliver sensor could be ready for human testing within six months.

Members of the John Glenn Biomedical Engineering Consortium include Case, NASA Glenn Research Center, the Cleveland Clinic Foundation, University Hospitals of Cleveland and the National Center for Microgravity Research.
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