The contact lenses used by 45 million people worldwide to improve their vision could someday help monitor health by sensing when levels of disease-indicating chemicals in tears change. Scientists believe lenses could one day diagnose dry-eye syndrome, glaucoma, or even cancer, with the ultimate hope that in the near future contacts could let the wearer know when something is wrong, before they have to go to the doctor.
A research team in the UK led by mechanical engineer and nanotechnology expert Haider Butt has developed a contact lens that can monitor glucose levels in tears in diabetics using an app that's available on most smartphones. The lenses work by slightly swelling when glucose is present, which changes the way light bounces off of them, similar to how a CD changes colors when you shift it in the light. Except instead of moving the contact lens to change the color, the change occurs when glucose concentrations increase. When a white light source is shined on the lens, the illumination can be detected using Lux, a light-measuring app available for Androids and iPhones.
Mohamed Elsherif, a Ph.D. candidate at the University of Birmingham and lead author of the research, published in ACS Nano in September, says that he originally set out to "develop a contact lens that would [visibly] change color according to glucose concentrations." But he found the development of that type of lens more complicated than expected. So he started with a lens that could react to glucose, but instead of watching it change color when levels were abnormal, a smartphone could measure and report the change during periodic blood sugar checks. To do this, he needed to embed a tiny matrix in a contact lens that could both change shape when glucose was present and disperse light differently before and after that shape changed.
He started by using a laser to carve out a precisely patterned matrix into a gel material, which would later be transferred to a commercial contact lens. Because of the regularity of the patterned walls, the matrix bends light in a very unique way that is specific to the spacing between the walls. Then, based on previously developed chemistry, molecules were embedded in the matrix that latch onto glucose when concentrations rise, but release it when they lower. Because these glucose-grabbers are embedded within the tiny matrix, when they latch onto glucose the matrix swells to make room for the sugar.
It's this swelling of the matrix that changes the way the lenses disperse light. Although the change is invisible to the naked eye, it can be measured with a smartphone light sensor. The change in light pattern is related to the amount of swelling, which corresponds to the amount of glucose.
This isn't the only contact lens that's been developed this year to monitor changes in tear glucose concentration. In January, a group in South Korea accomplished the technology by embedding glucose-splitting enzymes inside of contact lenses. The splitting reaction generates electrons, which could be monitored wirelessly. In May, research from the University of Maryland School of Medicine used fluorescent probes embedded in contact lenses to sense glucose. Back in 2014, Google announced plans to develop a glucose-sensing lens as well, although a product hasn't been released yet.
An important feature to consider in developing a continuous contact lens glucose monitor is shelf-life and reusability. Enzymes and fluorescent probes have the potential of degrading or fading over time, although the fluorescent contact lenses developed by the University of Maryland School of Medicine remained stable for three months, the same amount of time as Elsherif and his colleagues' recently released swelling lenses. As for reusability, Elsherif remarked that the lens his team developed showed similar efficacy after 300 cycles of glucose binding. Blood sugar fluctuates multiple times a day, depending on how often and how much a person eats and exercises.
Arguably the most exciting benefit of the contact lenses in the current work is that the measurement can be performed with a smartphone, putting it one step closer to consumer accessibility. However, Elsherif points out that a special light source is still required. He is continuing to work on a lens that would change from transparent to colored when glucose is present. He envisions the color change would be enough for the wearer to use a color coded key to read their sugar levels.
Glucose isn't the only thing that contact lenses could potentially measure. Elsherif says that the lenses could be tailored to sense other biomolecules as long as a gel matrix exists or can be developed that recognizes the molecule of interest. One example could be a specific protein present in tears that is a marker for a disease, such as glaucoma, cystic fibrosis, or herpes, to name a few. Someday people with perfect vision may don contact lenses that could help catch disease, all without stepping foot inside a doctor's office.
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