Angle-Independent Optical Moisture Sensors Based on Hydrogel-Coated Plasmonic Lattice Arrays
Angle-Independent Optical Moisture Sensors Based on Hydrogel-Coated Plasmonic Lattice Arrays
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DOI：
10.1021/acsanm.8b00268
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发表时间：
2018-03-01
影响因子：
5.9
通讯作者：
Kagan, Cherie R.
中科院分区：
文献类型：
--
作者：
Chen, Wenxiang;Wu, Gaoxiang;Kagan, Cherie R.
等离子体纳米结构为化学、生物和环境应用中的比色传感器提供了极好的平台。与现有的等离子体传感器库相比，我们报告了一种角度无关的光学传感器，该传感器被设计用于监测土壤湿度和在粗糙表面上操作。光学湿度传感器通过将水凝胶涂覆在纳米等离子体Au纳米棒晶格阵列的顶部上来构造，其中水凝胶在暴露于水分时的折射率变化被转换成阵列的共振的光谱偏移。一个修改后的朗缪尔吸附等温线模型被用来捕捉在传感器和周围环境之间的界面处的水吸附和解吸的动力学。纳米棒长度和纳米棒阵列间距被系统地调谐以解耦纳米棒的局部表面等离子体共振和纳米棒阵列的瑞利异常，从而产生具有角度无关共振（类似于0.2 nm/deg）的传感器。作为概念证明，我们将传感器放置在不平坦的土壤表面上，并展示了仅取决于土壤湿度的一致的传感器谐振偏移。具有角度无关共振的稳健、环保型光学水分传感器为智能土壤水分监测提供了一个有前途的传感平台，对于应对农业缺水的挑战至关重要。
Plasmonic nanostructures provide excellent platforms for colorimetric sensors in chemical, biological, and environmental applications. In contrast to the existing library of plasmonic sensors, We report an angle-independent optical sensor that is designed for monitoring soil moisture and operating on rough surfaces. The optical moisture sensor is constructed by coating hydrogel on top of an ultrathin, plasmonic Au nanorod lattice array, where the refractive index changes of the hydrogel upon exposure to moisture are transduced into spectral shifts of the resonances of the array. A modified Langmuir adsorption isotherm model is used to capture the dynamics of water adsorption and desorption at the interface between the sensor and the ambient environment. The nanorod length and the nanorod array pitch are systematically tuned to decouple the localized surface plasmon resonance of the nanorods and the Rayleigh anomalies of the nanorod array, creating sensors with angle-independent resonances (similar to 0.2 nm/deg). As a proof of concept, we place the sensor on uneven soil surfaces and demonstrate the consistent sensor resonance shift that only depends on the soil wetness. Robust, eco-friendly optical moisture sensors with angle-independent resonances provide a promising sensing platform for smart soil moisture monitoring important to tackle the challenge of water scarcity in agriculture.