Plasmonic contact lens materials for glucose sensing in human tears

Surface-enhanced Raman scattering (SERS) contact lens materials (SERS-LM) have been developed for selective glucose detection in human tears. SERS-LM is composed of a silk fibroin (SF) layer, a layer of silver nanowires (AgNWs) coated with 4-mercaptophenyl boronic acid (MPBA), and a protection film (PF) layer in a layer-by-layer structure. SF offers a biocompatible interface and filters tear proteins larger than nanopores in the SF domain. The MPBA-coated AgNWs (AgNWs-MPBA) formed on SF creates a high density of hotspots for Raman signal enhancement, and MPBA functions as a chemical receptor that induces cis-diol complexation with a glucose molecule. The developed SERS-LM exhibits excellent glucose sensing performance in the concentration range of 500 nM - 1 mM, and the limit of detection is 211 nM. Then, the sensing capability of the SERS-LM is demonstrated using human tears before and after a meal. The tear glucose levels measured by SERS-LM represent trends of corresponding blood glucose level, confirming the feasibility of the developed SERS-LM for noninvasive glucose sensing in human tears. The developed SERS-LM is expected to be applied for various wearable-type personal health monitoring systems.