Cerium Oxide Nanoparticle-Containing Colorimetric Contact Lenses for Noninvasively Monitoring Human Tear Glucose

Noninvasive methods for monitoring diabetes are being developed to eliminate the need for invasive finger-prick testing. Here, we propose the noninvasive detection of tear glucose using contact lenses that contain cerium oxide nanoparticles (CNPs). We chemically conjugated CNPs with glucose oxidase (GOx) using poly(ethylene glycol) (PEG) (CNP-PEG-GOx). GOx oxidizes glucose into hydrogen peroxide, which rapidly (∼1 min) reduces colorless Ce3+ to yellow Ce4+ with high sensitivity (>0.1 mM). Then, the yellow CNP-PEG-GOx can be analyzed to quantify the glucose concentration using a smartphone equipped with an image-processing algorithm. The CNP-PEG-GOx-laden contact lenses had physical properties similar to those of commercially available contact lenses and were nontoxic to human corneal cells and endothelial cells. When the CNP-PEG-GOx-laden contact lenses were placed on the eyes of diabetic rabbits, it was possible to measure the tear glucose levels. Interestingly, the lenses successfully detected glucose in human tear specimens and distinguished the diabetes status of patients. These findings suggest that the CNP-PEG-GOx-laden contact lenses could be used along with a smartphone-based image-processing algorithm to noninvasively monitor human tear glucose.