Chitosan based substrates for wound infection detection based on increased lysozyme activity

• Visual detection of wound infection at an early stage.
• A degree of N-acetylation of around 50% results best hydrolysis rates by lysozyme.
• Dyes of varying chemistry require different chitosan modification strategies.
• Successful prove of concept with human wound fluid samples.

There is a strong need of point-of-care diagnostics for early detection of wound infection. In this study, substrates based on functionalized chitosan were developed for visual detection of elevated lysozyme activity, an infection biomarker in wound fluids. For efficient hydrolysis by lysozyme, N-acetyl chitosan with a final degree of acetylation of around 50% was synthesized. N-acetylated chitosan and a chitosan-starch composite were labeled with structurally different dyes resulting in lysozyme-responsive biomaterials. Incubation with lysozyme in buffer and artificial wound fluid lead to a release of colored hydrolysis products already after 2 h incubation. Tests in human wound fluid from infected wounds indicated a clear visual color change after 2.5 h compared to control samples. A higher degree of swelling of the chitosan/starch containing substrate led to faster hydrolysis by lysozyme. This study demonstrates the potential of the lysozyme-responsive materials for diagnosis of wound infection and provides different diagnostic substrates for potential incorporation in point-of-care devices.