Introduction:
Metal-organic frameworks (MOFs) are crystalline supramolecular assemblies that are built up from precisely defined subunits by coordination or covalent interactions [1]. MOFs are usually highly porous, and they offer a wide range of applications where incorporation of guest molecules are needed. Applications include fuel storage, catalysis, drug delivery and gas sensing. Recently a layer-by-layer (LbL) method for building such materials has been introduced, which offers more control on the MOF structure. [1,2]Surface Plasmon resonance (SPR) is a highly sensitive optical method that measures changes in refractive index (RI) near a metal surface, even as small changes as 10-6 RI units. [3] In the Kretschmann configuration, the SPR signal is excited and measured from the “dry side” of a metal coated sensor slide, which makes it possible to measure highly light-absorbing or turbid solutions. Due to the high sensitivity, SPR has traditionally been a tool for biochemists for measuring biomolecular interactions in solution. However, because the SPR phenomenon is not selective, it can also be used for nanoscale material science as well. Apart from only measuring relative changes in the intensity at fixed angles or angular position, the SPR Navi 200 also allows collection of the complete SPR curve with absolute angle information thus enabling optical constants and thickness determination of nanoscale films both in gas and liquid phases.
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