In this work, a multilayer-modified paper-based colorimetric sensing platform with improved color uniformity and intensity was developed for the sensitive and selective determination of uric acid and glucose with smartphone as signal readout. In detail, chitosan, different kinds of chromogenic reagents, and horseradish peroxidase (HRP) combined with a specific oxidase, e.g., uricase or glucose oxidase (GOD), were immoblized onto the paper substrate to form a multilayer-modified test paper. Hydrogen peroxide produced by the oxidases (uricase or GOD) reacts with the substrates (uric acid or glucose), and could oxidize the co-immoblized chromogenic reagents to form colored products with HRP as catalyst. A simple strategy by placing the test paper on top of a light-emitting diode lamp was adopted to efficiently prevent influence from the external light. The color images were recorded by the smartphone camera, and then the gray values of the color images were calculated for quantitative analysis. The developed method provided a wide linear response from 0.01 to 1.0 mM for uric acid detection and from 0.02 to 4.0 mM for glucose detection, with a limit of detection (LOD) as low as 0.003 and 0.014 mM, respectively, which was much lower than for previously reported paper-based colorimetric assays. The proposed assays were successfully applied to uric acid and glucose detection in real serum samples. Furthermore, the enhanced analytical performance of the proposed method allowed the non-invasive detection of glucose levels in tear samples, which holds great potential for point-of-care analysis.

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在这项工作中，开发了具有改进的颜色均匀性和强度的多层改性纸基比色传感平台，用于通过智能手机作为信号读出灵敏和选择性地测定尿酸和葡萄糖。详细地，将壳聚糖，不同种类的生色试剂以及辣根过氧化物酶（HRP）与特定的氧化酶（例如尿酸酶或葡萄糖氧化酶（GOD））结合固定在纸质基材上，以形成多层改性的试纸。氧化酶（尿酸酶或GOD）产生的过氧化氢与底物（尿酸或葡萄糖）反应，并可以氧化共固定的生色试剂，并以HRP为催化剂形成有色产物。通过将试纸放在发光二极管灯顶部的简单策略，可以有效地防止外部光的影响。用智能手机照相机记录彩色图像，然后计算彩色图像的灰度值以进行定量分析。所开发的方法对于尿酸检测提供了0.01至1.0 mM的宽线性响应，对于葡萄糖检测提供了0.02至4.0 mM的宽线性响应，检测限（LOD）分别低至0.003和0.014 mM，远低于用于以前报道的纸基比色测定。所提出的测定方法已成功地应用于实际血清样品中的尿酸和葡萄糖检测。此外，所提出方法的增强分析性能允许无创检测泪液样品中的葡萄糖水平，

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