The use of metal-organic framework (MOF) thin films to detect water vapor across a wide concentration range is demonstrated using MOF-functionalized quartz surface acoustic wave (SAW) sensors. A range of 3-14,800 ppmv was obtained with thin films of the MOF Cu(3)(benzenetricarboxylate)(2) (Cu-BTC) deposited by an automated layer-by-layer method. Devices coated by a manual technique demonstrated sensitivity from 0.28 to 14,800 ppmv, the limit of our test system. This exceeds the sensitivity of many commercially available sensors. Cu-BTC layers were covalently bonded directly to the silicon oxide surface, allowing devices to be heated beyond 100 °C to desorb water adsorbed in the pores without decomposition, thereby regenerating the sensors. Sensor response as a function of coating thickness was evaluated, showing that the SAW sensor response is bounded by maximum and minimum layer thicknesses. Computer simulation of H(2)O uptake shows a multistep adsorption isotherm defined by initial adsorption at open Cu-sites, followed by pore-filling and finally full saturation. Modeling and experimental results are consistent. Calculated uptake values suggest an efficient adsorption of H(2)O by Cu-BTC. These results provide the first convincing evidence that MOF functionalization of compact sensing technologies such as SAW devices and microcantilevers can compete with state-of-the art devices.

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The analytical utility of Combining low-temperature sample preparation procedures with two-photon excitation (TPE) of fluorescence spectrometry has been explored. A 10 K durene crystal was used as the sampling medium for methyl derlvatives of naphthalene. I n order io minimize problems caused by the low TPE efflclency, a photomultlpller tube was placed directly In front of the sample, using a (UV transmitting) filter to protect the tube from laser scatter. Because of the high resolution of the TPE peaks (0.5-1.7 cm-' fwhm bandwidth), each component of a nine-component methylnaphthalene mlxture could be Identifled from a single TPE scan. Likewise, the major methylnaphthalene components In a raw shale oil sample prepared In a durene crystal (without prior separations) could also be Identifled from a single TPE scan. It has been demonstrated that femtogram quantities of some methylnaphthalene derivatlves can be detected and that the TPE detection limits are 1 to 2 orders of magnltude higher than those obtained with UV excitation of fluorescence.Relatively few analytical applications of two-photon excitation (TPE) of fluorescence spectrometry appear in the literature in spite of the fact that it is recognized that the polarization properties of TPE and the differing one-and twophoton selection rules can be exploited for qualitative analysis ( I , 2). At present TPE of fluorescence spectrometry apparently has not been successfully utilized for the characterization of multicomponent, isomeric mixtures of organic molecules. The reason for this is that previous analytical applications of TPE utilized samples prepared in room-temperature solutions. The broad absorption and fluorescence bands which are characteristic of organic compounds prepared in solution greatly complicate multicomponent analysis, regardless of the method in which fluorescence is induced.In contrast, laser-induced fluorescence (LIF) spectrometry has proven to be highly useful for the characterization of multicomponent mixtures of polycyclic aromatic hydrocarbon (PAH) isomers when low-temperature sampling techniques are utilized (3-9). The success of LIF methodologies can be attributed to two primary factors (3, 5 , 7, 8). First, highresolution absorption and fluorescence bands result when a PAH is prepared in a suitable low-temperature sampling medium, such as a Shpol'skii matrix. Second, a tunable monochromatic excitation source (Le., a dye laser) can be tuned to the narrow absorption line of the analyte, which will therefore be selectively excited. The presence of the analyte can be confirmed by the highly resolved and well-defined structure of the low-temperature fluorescence spectrum. Thus, each component of a complex mixture can, in principle, be identified by tuning the dye laser to a suitable absorption line and obtaining the resulting fluorescence spectrum.The primary purpose of this paper is to assess the analytical advantages of combining low-temperature sample preparation procedures with TPE of fluorescence spectrometry. In anticipation of t...