Yang Fan, Hlushko Raman, Wu Di, Sukhishvili Svetlana A, Du Henry, Tian Fei
Department of Chemical Engineering and Materials Science, Stevens Institute of Technology, Hoboken, New Jersey 07030, United States.
Department of Materials Science and Engineering, Texas A&M University, College Station, Texas 77843, United States.
ACS Omega. 2019 Jan 28;4(1):2134-2141. doi: 10.1021/acsomega.8b02823. eCollection 2019 Jan 31.
Rapid, accurate, and real-time measurements of ocean salinity are of great importance for a host of scientific, commercial, and defense applications. We demonstrate a highly sensitive, fast-responding fiber-optic salinity sensor that integrates long-period fiber gratings (LPFGs) with ionic strength-responsive hydrogel. The submicron-thick hydrogel was synthesized via layer-by-layer electrostatic assembly of partially quaternized poly(4-vinylpyridine) (qP4VP) and poly(acrylic acid), followed by chemical cross-linking. Spectroscopic ellipsometry measurement of a hydrogel made of 37% quaternized qP4VP showed robust and reversible swelling/deswelling in solutions with salt concentrations ranging from 0.4 to 0.8 M (22.8-44.7 g/kg) around pH 8.1. The swelling/deswelling process induced large changes in the refractive index of the hydrogel, leading to resultant shift in the resonance wavelength (RW) of LPFGs. The salinity-dependent optical response of the hydrogel-coated LPFGs is in good agreement with ellipsometry measurement. LPFGs coated with the hydrogel exhibited a sensitivity of 7 nm RW shift/M (125.5 pm/‰) with a measurement time less than 5 s. The shift in the resonance wavelength correlated linearly with salt concentration, making quantification of measured salinity straightforward.
快速、准确且实时地测量海洋盐度对于众多科学、商业和国防应用都极为重要。我们展示了一种高度灵敏、响应迅速的光纤盐度传感器，该传感器将长周期光纤光栅（LPFG）与离子强度响应水凝胶集成在一起。通过部分季铵化的聚（4-乙烯基吡啶）（qP4VP）和聚丙烯酸的逐层静电组装，随后进行化学交联，合成了亚微米厚的水凝胶。对由37%季铵化的qP4VP制成的水凝胶进行光谱椭偏测量表明，在pH值约为8.1、盐浓度范围为0.4至0.8 M（22.8 - 44.7 g/kg）的溶液中，水凝胶具有强烈且可逆的溶胀/去溶胀现象。溶胀/去溶胀过程导致水凝胶的折射率发生大幅变化，进而使LPFG的共振波长（RW）产生相应偏移。涂覆水凝胶的LPFG的盐度依赖性光学响应与椭偏测量结果高度吻合。涂覆水凝胶的LPFG表现出7 nm RW偏移/M（125.5 pm/‰）的灵敏度，测量时间小于5秒。共振波长的偏移与盐浓度呈线性相关，使得测量盐度的定量变得直接明了。
