Competence Centre for Electrochemical Surface Technology, 2700, Wiener Neustadt, Austria.
AIT Austrian Institute of Technology GmbH, 3430, Tulln an der Donau, Austria.
Anal Bioanal Chem. 2020 May;412(14):3299-3315. doi: 10.1007/s00216-020-02452-8. Epub 2020 Feb 27.
Spectroscopy with planar optical waveguides is still an active field of research for the quantitative analysis of various supramolecular surface architectures and processes, and for applications in integrated optical chip communication, direct chemical sensing, etc. In this contribution, we summarize some recent development in optical waveguide spectroscopy using nanoporous thin films as the planar substrates that can guide the light just as well as bulk thin films. This is because the nanoporosity is at a spacial length-scale that is far below the wavelength of the guided light; hence, it does not lead to an enhanced scattering or additional losses of the optical guided modes. The pores have mainly two effects: they generate an enormous inner surface (up to a factor of 100 higher than the mere geometric dimensions of the planar substrate) and they allow for the exchange of material and charges between the two sides of the solid thin film. We demonstrate this for several different scenarios including anodized aluminum oxide layers for the ultrasensitive determination of the refractive index of fluids, or the label-free detection of small analytes binding from the pore inner volume to receptors immobilized on the pore surface. Using a thin film of Ti metal for the anodization results in a nanotube array offering an even further enhanced inner surface and the possibility to apply electrical potentials via the resulting TiO semiconducting waveguide structure. Nanoporous substrates fabricated from SiN thin films by colloid lithography, or made from SiO by e-beam lithography, will be presented as examples where the porosity is used to allow for the passage of ions in the case of tethered lipid bilayer membranes fused on top of the light-guiding layer, or the transport of protons through membranes used in fuel cell applications. The final example that we present concerns the replication of the nanopore structure by polymers in a process that leads to a nanorod array that is equally well suited to guide the light as the mold; however, it opens a totally new field for integrated optics formats for direct chemical and biomedical sensing with an extension to even molecularly imprinted structures. Graphical abstract.
平面光波导光谱学仍然是各种超分子表面结构和过程的定量分析以及集成光学芯片通信、直接化学传感等应用的活跃研究领域。在本贡献中，我们总结了使用纳米多孔薄膜作为平面基底的光波导光谱学的一些最新进展，这些薄膜可以像体薄膜一样很好地引导光。这是因为纳米多孔性处于远远低于导波光波长的空间长度尺度，因此不会导致光导模的散射增强或额外损耗。这些孔主要有两个作用：它们产生巨大的内表面（比平面基底的纯几何尺寸高多达 100 倍），并且允许在固体薄膜的两侧之间进行物质和电荷的交换。我们将通过几种不同的情况来证明这一点，包括用于超灵敏地测定流体折射率的阳极氧化铝层，或者从孔内体积结合到固定在孔表面上的受体的小分析物的无标记检测。使用 Ti 金属薄膜进行阳极氧化会导致纳米管阵列，从而提供进一步增强的内表面，并有可能通过由此产生的 TiO 半导体波导结构施加电势能。通过胶体光刻或电子束光刻制造的 SiN 薄膜或通过 e 束光刻制造的 SiO 纳米多孔基底将作为例子，其中多孔性用于允许在光导层顶部融合的束缚脂质双层膜中离子通过，或者在燃料电池应用中使用的质子通过膜。我们呈现的最后一个例子涉及通过聚合物复制纳米孔结构的过程，该过程导致纳米棒阵列，其同样适合引导光，而无需模具；然而，它为直接化学和生物医学传感的集成光学格式开辟了一个全新的领域，甚至可以扩展到分子印迹结构。
