ISSCC 2011: Sorry, There's a Solar-Powered Sensor in My Eye

Researchers explain future biomedical gadgetry for vision, cancer monitoring, and glaucoma

2 min read
ISSCC 2011: Sorry, There's a Solar-Powered Sensor in My Eye

This cubic millimeter-sized sensor's creators at the University of Michigan hope that future iterations of this proof-of-concept gizmo could help thwart optical nerve damage caused by glaucoma. It was one of several gadgets presented yesterday during a biomedical session at the 2011 International Solid-State Circuits Conference.

Gregory Chen explained that his team designed the device for implantation in the eye's anterior chamber, which is out of the field of vision and already routinely accessed for cataract surgery. The device itself includes a MEMS sensor which determines pressure by monitoring the movements of capacitor plates. Most of the device is encased in a glass housing which relies on the iris's elasticity to hold it in place. They designed the device to measure and record pressure every 15 minutes, but it is meant to transmit it only once a day--to a wand that's held up to the patient's face. Storing enough energy for even one daily transmission was a challenge in such a tiny device, Chen says, so it relies not only on a custom-made, thin-film Lithium battery but also a tiny solar cell for harvesting more energy. Yes, a solar cell in your eye.

Chen explained that the device needs some 10 hours of indoor lighting or 1.5 hours of sunlight per day to get enough energy. When a senior researcher on the project Dennis Sylvester gave a preview on Sunday night someone in the audience asked if a user might charge it more quickly by staring directly into the sun. Sylvester said that wasn't the best idea… 

Another presentation in the biomedical session questioned the best way to transfer data into the body--and as a specific example, again, into the eye. But this time, instead of transmitting pressure data out, Maurits Ortmanns of Ulm University in Germany described beaming data in for nerve stimulation as a vision aid for the blind. He explained the dilemma of getting a lot of information in without large amounts of power dissipation (not so good for eyeball tissue). As a solution, he proposed an infrared data link with an implanted photodetector and to get a data stream of up to 2Mb/s.

Yet, talk was not limited to eyeballs: Roxana Heitz of Stanford University described a method developed with Santa Clara-based National Semiconductor, for long-term cancer progression monitoring. The basics behind her technique: inject subject with fluorescent dyes which bind to cancer-related molecules, emit laser light, and watch progression of cancer. That's already possible, she says, but requires bulky instruments. For this research she integrated the essential electronics into a 1 centimeter cubed, 0.7 g device. She tested it in rodents and could monitor the dye while they freely roamed--well, almost freely. That proof-of-concept version required a cord to read the device's digital output, but she imagines that future versions would be completely implantable.

Image: Gyouho Kim

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