Smart contact lens puts glucose monitoring in focus

Wearable continuous glucose monitoring (CGM) devices promise a new age in diabetes management, that is easy and convenient for patients. Researchers have now developed a smart contact lens that can monitor glucose levels in tears in real time, relaying the information to patients via a smartphone [Han et al., Biomaterials 302 (2023) 122315, https://doi.org/10.1016/j.biomaterials.2023.122315].

The team from Pohang University of Science and Technology, The Catholic University of Korea, and PHI BIOMED Co. fabricated smart contact lenses with new bimetallic electrodes based on hyaluronate-coated gold-platinum (Au@Pt) that improve long-term stability in the eye.

“Smart contact lenses for CGM using an electrochemical glucose sensor have suffered from the relatively low stability of electrodes and sensors inadequate for further clinical applications,” explains Sei Kwang Hahn, who led the study.

Commercial electrochemical glucose sensors typically rely on Pt for working and counter electrodes because of the metal’s excellent electrocatalytic reactivity. When deposited on a polymer substrate, such as poly(ethylene terephthalate) (PET), however, the metal’s lack of ductility and the large difference in thermal expansion coefficients results in cracking that degrades performance and leads ultimately to device failure. The new bimetallic electrodes, produced by alloying Pt with other metals such as Au, get around this shortcoming.

“We used Au thin film as a stress relaxation layer with a low surface energy and a lattice constant similar to that of Pt,” Hahn explains.

The reduced difference in thermal expansion coefficients between Au@Pt and PET minimize cracking, while passivation of the Au@Pt bimetallic electrode with branch-type thiolated hyaluronate (HA) improves the stability further by preventing dissolution of Au by Cl^– ions present in tears.

“[We] increased the stability of smart contact lenses by fabricating thin-film electrodes with minimal physical defects (cracks) and electrochemical defects (Au dissolution),” he points out.

The new glucose sensor contact lens, which includes an RF system for wireless power supply and an ASIC chip for wireless communication, was tested in diabetic rabbits for three weeks. The level of glucose in tears correlates well with blood glucose levels, even as levels increase and decrease in real time, providing an accurate measure for monitoring diabetes.

“Our smart contact lens with optimized electrodes enables the accurate and long-term real-time glucose monitoring of normal and diabetic rabbits,” says Hahn. “Smart contact lenses could be better than CGM devices for accurate and long-term stable monitoring of glucose levels for the diagnosis of diabetes,” he suggests.