Lysozyme, often termed “the body’s own antibiotic,” is vital in the eye’s defence against infection. Present in tears, saliva, and other secretions, it is a key biomarker for various ocular diseases, and lysozyme concentration can provide useful insights into eye health.1,3,4
Also known as muramidase or N-acetylmuramic acid hydrolase, lysozyme is a small, stable protein held together by four disulfide bonds. Its primary role is to break down the peptidoglycan layer in bacterial cell walls by cleaving the β-1,4-glycosidic bonds between N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG). By breaking this layer, the protein triggers bacterial lysis, particularly effective against Gram-positive bacteria.
Gram-negative bacteria, however, are more resistant to attack due to their protective outer membrane, which shields the peptidoglycan layer underneath.
Recent research has also demonstrated lysozyme’s non-catalytic antimicrobial roles, suggesting it contributes to immune defence beyond its enzymatic function. In the eye, it is produced not only in tear fluid but also by retinal pigment epithelial cells, with its expression regulated in response to infection.
With this in mind, scientists at the Institute of Solid State Physics have developed a soft, wearable sensor in the form of a fluorescent hydrogel eye patch. Its design aims to avoid the associated problems in current detection methods, which are often invasive or require bulky lab equipment. The research has been published in Analytical Chemistry.
A New Approach To Tear Analysis
The eye patch is built around a multi-emission metal-organic framework (MOF) hydrogel, created by coordinating europium (Eu3+) and dysprosium (Dy3+) ions with 5-boronobenzene-1,3-dicarboxylic acid. This Eu-Dy MOF gel emits visible fluorescence under UV light, making it ideal for optical sensing.
When placed beneath the eye, the patch passively collects tear fluid. On exposure to ultraviolet light, the MOF gel emits a distinctive blue glow. This fluorescence is then captured using a smartphone camera, and the images are analysed with colour recognition software to estimate the lysozyme concentration in the tears.
How The Sensor Works
The MOF hydrogel relies on the “antenna effect.” Organic ligands in the hydrogel absorb UV light and transfer the energy efficiently to the embedded lanthanide ions, Eu3+ and Dy3+, which then emit strong, colour-specific fluorescence.
When lysozyme interacts with the gel, it forms complexes that quench the fluorescent energy state by static quenching and electron transfer. This change in fluorescence allows for the detection of lysozyme concentrations as low as 1.5 nm.
When excited at 275 nm, the hydrogel emits bright blue fluorescence. As the lysozyme concentration changes, so does the intensity of the glow, providing a clear, measurable signal that correlates with tear composition.
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Real-Time, Reliable Monitoring
Integrated into a soft patch, this material allows for real-time, on-body monitoring. In testing, the eye patch achieved recovery rates for tear fluid samples ranging from 94 % to 110 %, suggesting high accuracy and repeatability.
The approach combines convenience with precision: no lab equipment is needed to collect samples, and results can be captured and analysed using only a smartphone. This makes it particularly promising for point-of-care diagnostics, at-home health monitoring, and even early warning systems for ocular diseases.
Future Applications
While the patch was designed to monitor lysozyme, the broader technique could be used for tracking other biomarkers in tears and bodily fluids. It’s a step towards noninvasive, wearable diagnostics that combine advanced chemistry with everyday usability.
Journal Reference
- Smart eye patch uses fluorescence to monitor eye health [Online] Available at https://www.eurekalert.org/news-releases/1096420 (Accessed on 09 September 2025)
- Pan, L., Yang, F., Kang, X., Zhang, Q., Jiang, C. (2025). Rare Earth Ion-Induced Functionalized Fluorescent MOF Hydrogel Patches for Monitoring Lysozyme in Tears. Analytical Chemistry. DOI: 10.1021/acs.analchem.5c00346, https://pubs.acs.org/doi/10.1021/acs.analchem.5c00346
- Ferraboschi, P., Ciceri, S., Grisenti, P. (2021). Applications of Lysozyme, an Innate Immune Defense Factor, as an Alternative Antibiotic. Antibiotics, 10(12), 1534. DOI: 10.3390/antibiotics10121534, https://www.mdpi.com/2079-6382/10/12/1534
- Nawaz, N. et al. (2022). Lysozyme and Its Application as Antibacterial Agent in Food Industry. Molecules, 27(19), 6305. DOI: 10.3390/molecules27196305, https://www.mdpi.com/1420-3049/27/19/6305
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