New biosensing contact lenses are designed to detect glucose levels for diabetics and hold thousands of other possibilities.
Could something as simple as a contact lens save someone’s life? A new transparent array of sensors that fits between two layers of a contact lens promises to do exactly that by continuously monitoring blood chemistry to detect even the slightest changes in a person’s health.
The research, published in the American Chemical Society's journal Applied Materials & Interfaces, was conducted by Gregory Herman, a chemical engineering professor at Oregon State University. His initial prototype monitors glucose levels in the human eye, something that diabetics must constantly measure.
“I have a friend who has type 1 diabetes and he has to poke himself ten times a day to measure his blood glucose concentration, so he knows whether to inject insulin or go get something to eat,” Herman said.
Contact lens sensors that measure sugar in blood moving through the eye would simplify diabetes management for millions of people worldwide, he added. The chemistry underlying the sensors is adaptable enough to potentially monitor heart rate, body temperature, stress, hormones and proteins, and signs of disease.
Transistors to Sensors
Herman’s system involves embedding a thin, clear polymer layer of semiconductor sensors and electronics between two layers of a flexible hydrogel plastic. The resulting sandwiches are comfortable, safe, and permeable enough for blood to penetrate and interact with the sensors. They can even be fitted to correct vision.
The researchers began investigating contact lens sensors more than a decade ago, but they were stymied by their inability to make truly transparent electronics that could monitor blood chemistry continuously.
Then, in 2012, Herman and his team began studying the chemistry of indium gallium zinc oxide semiconductors. IGTO field-effect transistors (IGZO-FETs) can be made very thin and completely transparent. In fact, a thin layer of IGZO transistors made Apple’s ultralight iPad Air possible by replacing a thick, heavy layer of alpha-silicon electronics. Using similar technology, Herman believes he could build 2,500 sensors on a single contact lens, enough to detect the early biomarkers of such diseases as breast cancer, colon cancer, renal disease, heart disease, and kidney failure.
Herman’s team discovered that they could turn those transistors into sensors by modifying their surfaces with glucose oxidase, an enzyme that reacts with glucose. This changes the electrical response of the transistor, which is how it detects subtle changes in glucose level. If glucose levels rise or fall too far, the circuitry on the contact lens transmits an alert via Bluetooth (or another protocol) to a cell phone to sound the alarm or call a medical professional. It could also activate an insulin pump to administer medication without any patient intervention.
“The contact lens will only send a signal when it sees something unnerving, like if your glucose levels are too high,” Herman said. “It would also track levels throughout the day and then also track it throughout the week or year so the person will know when they need to be careful or if there is an activity they should change for a better lifestyle.”
Customized Printing
The sensors are so thin – at 12.5 microns, about as wide as plastic wrap – that the power requirements to run the sensors are incredibly low. In fact, the electronics could scavenge a charge from the smartphone’s radio frequency queries, store it in a capacitor, and use the energy to operate the transistors and transmit the results. Other power options include an enzymatic fuel cell to convert the chemical energy of glucose to electricity, or a small photovoltaic cell, though it would not charge the lens at night, Herman said.
Traditional lithography methods would not work for the curved design. Herman solved this by using microcontact printing to pattern the electrodes onto the semiconductor substrate. He then used an e-jet printer, an inkjet printer customized to handle biochemicals, to apply a 1-micron-thick pattern of glucose oxidase enzyme over the transistors. The e-jet printer produces much finer prints than a conventional inkjet, which is limited to about 50 microns. Ultimately, he hopes to print a variety of sensors by changing the “ink” in the system to print different types of enzymes.
The combination of conventional semiconductor processing and e-jet printing keeps the lenses very affordable. “We are hoping we can manufacture the lenses at a low enough cost that they are easily replaceable and you could change them out every day or every week,” Herman said.
The lenses could prove affordable enough for developing countries to reduce their reliance on expensive, hard-to-transport equipment. Herman isn’t positive how long it will take the lenses to get on the market, but he believes five years is a pretty safe guess.
“It could be even quicker,” he said. “Anyone can wear them. There won’t be a sacrifice for vision, health, or even comfort. I am very excited to see the possibilities.”
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