Photonic Hydrogel Sensing System for Wearable and Noninvasive Cortisol Monitoring

Abstract

Wearable biosensors have emerged as an increasingly important tool in personalized health monitoring and are even envisioned to renovate the traditional centralized diagnosis method to home diagnosis. Here, we introduce two types of wearable devices with sandwich structures that utilize photonic crystal hydrogel biosensors with structural color for the detection of cortisol in human sweat. The integrated biosensors exploit molecular imprinting and antibody–antigen competitive binding techniques, which are tailored to different storage and detection requirements for use. By using a smart phone to analyze the color change of the hydrogel, the dynamic fluctuations of endogenous cortisol in sweat during the diurnal cycles were monitored. The detection limit reached the nmol/L level, meeting the detection requirements in body fluids. Furthermore, the Trier Social Stress Test and exercise for specific periods of time were used to verify the relevance of cortisol as a stress biomarker and the sensitivity of the developed biosensors. The development of wearable devices for noninvasive and naked eye detection in this study offers a personalized approach to stress self-management.

可穿戴光学汗液传感器的研究进展

“…软光刻技术等进行微流控装置的加工与制造 [27][28][29][30][31] 。Liu 等 [28] 构建的可穿戴微流控芯片的通道 层与封装层均由 PDMS 制成(图 2c)，具有良好的生物相容性与灵活性。 但 PDMS 在性能上还存在一定的缺陷，例如外表疏水、自身粘附性不强等，通常需要 进一步改性处理后才能更好地应用。 利用等离子体处理和化学修饰法对微流控装置的 PDMS 通道层进行亲水处理后， 微通道在负毛细管压力的作用下可以很容易地将汗液快速吸入通道 以完成后续检测 [31] 。等离子体处理操作简单，可以使 PDMS 表面亲水化。为了得到更持久 的亲水效果，可在等离子体处理后利用化学修饰法在其表面引入亲水基团，以进一步提高其 亲水性 [31] 。另外，为了提高 PDMS 的皮肤粘附性，Yuan 等 [32] 通过在 PDMS 中添加聚乙氧基 乙烯亚胺(polyethylenimine ethoxylated，PEIE)进行改性，制成粘性、柔性及可伸缩性更强 的集收集、输送和储存汗液为一体的可穿戴微流控装置。该装置可以完美地贴合皮肤，提高 汗液的收集效率。 2.2.2 水凝胶 水凝胶自身具有良好的吸湿性以及生物相容性等特性， 通过对水凝胶进行功能化修饰可 以用于特异性识别。Siripongpreda 等 [33] 将 pH 指示剂和葡萄糖酶等生物分子添加到制备的羧 甲基纤维素/细菌纤维素水凝胶中制备出可用于汗液 pH 和葡萄糖检测的比色传感器。 用该水 凝胶传感器进行检测时，所需样品量少且响应速度快。其中，pH 比色传感器的线性检测范 围为 pH 4.0 -9.0， 葡萄糖比色传感器的线性检测范围为 0 -0.5 mM， 检测限低至 2.5×10 -2 mM。 该水凝胶传感平台的提出为可穿戴传感器的设计开辟了新途径。Wang 等 [34] 通过简单的溶剂 置换法把比色试剂引入合成的聚乙烯醇/蔗糖水凝胶中，然后利用水凝胶的自愈合特性，将 含有比色试剂的水凝胶组装在水凝胶基底上形成可穿戴汗液分析贴片， 可用于汗液中生物标 志物的原位比色检测。Hu 等 [35] 通过将上转换荧光探针嵌入到多孔聚丙烯酰胺水凝胶中制成 水凝胶贴片， 其可利用内部滤光效应避免自然光、 背景荧光等因素的干扰以提高检测灵敏度。 将该贴片与便携式传感平台相结合，可用于人体汗液尿素水平的可视化检测(图 2d)。Li 等 [36] 通过在水凝胶中掺入比色试剂，开发出能够用于汗液中氯离子与葡萄糖检测的水凝胶 贴片，制备简单，成本低廉。Qin 等 [37] 利用分子印迹聚合物技术和抗原-抗体结合技术开发 出两种可用于汗液皮质醇无创检测的光子水凝胶传感器， 通过分析光子水凝胶的结构颜色变 化来检测物质浓度。 F o r R e v i e w O n l y 中国科学: 化学 http://chemcn.scichina.com…”

Host–Guest Interaction and Hydrogen Bonding Cross-Linking Actuated Smart Two-Dimensional Photonic Hydrogel Sensor of l-Histidine

“…Two-dimensional photonic crystals (2DPC) can be easily and fast fabricated and have a special Debye diffraction effect, and the Debye ring diameter is related to the particle spacing of the 2DPC . Hydrogels are one of the most promising responsive materials in the field of sensing due to their good flexibility and easy modification. , The 2DPCH formed by embedding a 2DPC array in a hydrogel undergoes volume contraction or expansion upon the special interaction of the recognition unit on the hydrogel chains with the target molecules. In consequence, the particle spacing of the embedded 2DPC changes, which is manifested as a change in the Debye ring diameter of the 2DPC.…”