A Smartphone-Assisted Schirmer Strip for Rapid Dual Colorimetric Sensing of Tear Glucose and pH Level

Although tear biomarkers are routinely determined using various clinical methods, most current techniques are complex, time-consuming, and require expensive equipment. Therefore, point-of-care (POC) testing is attracting considerable attention for rapid and noninvasive analyses. Here, we present a dual-function colorimetric Schirmer strip for the simultaneous determination of tear glucose and pH using the naked eye and image processing software. In our approach, horseradish peroxidase-glucose oxidase nanoflowers (HRP-GOx@NF) are used for glucose detection, and red cabbage-derived anthocyanins are used as a pH-sensitive, nontoxic indicator. In glucose detection, the catalytic stepwise reaction of HRP-GOx@NF produced a distinct blue color within 30 s by enabling the rapid oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of glucose, and this optimized platform exhibited a visual detection limit of 0.5 mM. Additionally, the anthocyanin-modified Schirmer strip simultaneously displayed distinct color transitions in response to varying pH values of the artificial tear fluid. This work presents a novel multiparametric paper platform that uniquely upgrades standard Schirmer strips for simultaneous, single-step tear collection, glucose sensing, and pH mapping without altering fluid flow. Like this, it demonstrates a rapid, cost-effective, and easy-to-prepare diagnostic tool offering significant advantages over conventional methods.