基于柔性衬底的光学氢气传感新机理及其应用研究

Due to the benefit of remote read-out and not being affected by electromagnetic interference, the optical hydrogen sensor has been considered as a promising candidate for hydrogen detection. However, the optical sensors generally have relatively low sensitivity and short life, which severely restricts their practical applications. We found that a palladium film deposited on polydimethylsiloxane (PDMS) can obtain a dramatic reflectance reduction, which results in an exceedingly high reflectance contrast of 25.78 upon exposure to 4 vol% hydrogen gas mixed with nitrogen gas. This result is twice higher than the best level of the optical hydrogen sensors based on Pd film and Pd-related nanostructures on rigid substrates. Such a high optical contrast is conflicted by the existing sensing mechanism based on the optical parameter change of the Pd film after hydrogenation. In this proposal, we will focus on the underlying physics of this phenomenon, for example, how the surface corrugations of hydrogen-sensitive materials influence the optical properties of the sensor, and how the ‘soft contact’ interface between the hydrogen-sensitive materials and flexible substrate as well as the geometries of the nanostructures relive the stress in the interface. Based on this novel sensing mechanism, we will fabricate and demonstrate an ultrasensitive and reliable visual optical hydrogen sensor. Meantime, we will also study the modulation mechanism of hydrogen-regulated active plasmonics and develop a cost-effective and high-throughput nanofabrication method to prepare the hydrogen-sensitive nanostructures in the flexible substrates, as well as experimentally demonstrate their performance in active plasmonics. Base on the novel modulation mechanism, we will further explore the full potential of the deformable hydrogen-sensitive nanostructures in the plasmonic dynamic display applications.

光学氢气传感器具有远程读出、抗电磁干扰等其它类型氢气传感器所不具备的优势，因此被认为是极具应用前景的氢气传感候选。但是，光学氢气传感器的低灵敏度和短寿命一直是限制其商业化的一个致命缺陷。我们发现柔性衬底上钯膜在吸氢前后的反射率发生巨大下降，其光学反差值是目前报道的钯基光学氢气传感器最好水平的3倍。如此高的光学反差不能用目前普适的介电常数变化理论来解释。在本申请项目中，我们将重点探索该奇异现象背后的物理机制，例如氢敏薄膜表面形变对其光学特性演变的作用机制，氢敏材料/柔性衬底的“软接触”界面以及特殊纳米结构对氢化过程中界面应力的释放机制等。基于这些机制，我们将制备并演示高灵敏度、高稳定性的可视化光学氢气传感。此外，我们还将探索表面等离激元的氢气调控机理，发展出柔性衬底上氢敏微纳结构的制备工艺，演示快速、高调制深度的表面等离激元动态调控，并将之应用到动态显示上，实现其应用价值。

由于具有高灵敏度、较快的响应时间和成熟的集成技术，电学氢气传感器主导着目前的氢气传感市场。但是电学传感器存在一个致命缺点：氢气和芯片的接触点可能产生电火花，存在爆炸的安全隐患。而光学传感器则可以通过远程读出来规避这种风险。然而，传统的光学氢气传感器灵敏度较低，这是因为传统的光学传感器都是基于刚性衬底的，其传感机制主要依赖于氢敏材料吸氢之后的介电常数变化，而吸氢引起的体积膨胀效应受到了极大的限制。在本项目中，为了克服这个问题，本团队首次发现了平整钯膜在柔性衬底上吸氢膨胀而引起的“镜面反射—漫反射”转化现象，并提出了基于这一新机理的高性能光学氢气传感器。这个新传感机制极大地放大了由吸氢应力带来的几何效应，在力学和光学上协同增强了传感灵敏度。该传感器在整个可见区都可以实现高达25的光学反差（同类器件最好水平的3倍以上），因此无需依赖任何科研设备（如高波长分辨率的探测器等等）。基于 “镜面反射—漫反射转化”的新光学传感机制，我们已经将之器件化。在氢气报警器原型器件测试中，我们的氢气浓度检测限为0.1%（1000 ppm），在4%氢气浓度下，响应时间达到1s以下。这表明了我们的氢气报警器有望应用到加氢站以及工业过程控制领域。此外，我们还把“镜面反射—漫反射”传感机制推广到光学气压传感上。其传感灵敏度，比传统的光学气压传感提高了3—4个数量级。我们进一步将上述光学气压传感器作为读出装置来定量检测早期肝癌的标志物甲胎蛋白（AFP），其线性范围可达0.05-132 ng/ml，检测限达到0.018 ng/ml，均已达到临床检测的要求。同时，良好的特异性进一步表明我们的光学气压生物传感器有望作为一个即时检测（POCT）设备应用于实际中。