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

Abstract 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.