Micrometers

In a move that takes sci-fi tech a step closer to reality, scientists have developed a super-thin battery that could be used to power smart contact lenses and even charge up using tears.

Smart contact lenses are not just an object of spy movie fiction; they’ve been in the works for a while. Researchers have attempted to create lenses for a variety of uses, including monitoring glucose levels, potentially detecting cancer, and in Black Mirror-esque fashion, taking photos with our eyes.

However, an obstacle to their development has been how to power them, in both a safe and convenient way. With existing batteries relying on wires containing metal – unsafe for the naked eye – researchers at Nanyang Technological University Singapore looked to the eye itself for more biocompatible inspiration.

"This research began with a simple question,” said Lee Seok Woo, lead author of the study, in a statement. “Could contact lens batteries be recharged with our tears? There were similar examples for self-charging batteries, such as those for wearable technology that are powered by human perspiration.”

The team developed a bio-safe battery that was 0.5 millimeters (0.02 inches) thin – about the same thickness as the human cornea. Using tears as their template, the battery was coated with an enzyme called glucose oxidase, which reacts with the sodium and chloride ions found in tears in a process known as reduction. The battery also contains water, acting like "circuitry" for electricity to be generated.

“It relies on just glucose and water to generate electricity,” explained Woo, “both of which are safe to humans and would be less harmful to the environment when disposed, compared to conventional batteries."

To test how it might function, the researchers placed the battery in a simulated eye, using saline solution to imitate tears. It successfully powered up, having produced a current of 45 microamperes and a maximum power of 201 microwatts. They also found that it could discharge power up to 200 times, only around 100 times less than a typical lithium-ion battery.

With a starting point that was already enough to power a smart contact lens, the team has suggested that future work will aim to improve the amount of electrical current the battery can produce.

For more smart contact lens developments, keep your eyes peeled.

The study is published in the journal Nano Energy.