Micromechanical photothermal infrared spectroscopy is a promising technique, where absorption-related heating is detected by frequency detuning of microstring resonators. We present photothermal infrared spectroscopy with mechanical string resonators providing rapid identification of femtogram-scale airborne samples. Airborne sample material is directly collected on the microstring with an efficient nondiffusion limited sampling method based on inertial impaction. Resonance frequency shifts, proportional to the absorbed heat in the microstring, are recorded as monochromatic IR light is scanned over the mid-infrared range. As a proof-of-concept, we sample and analyze polyvinylpyrrolidone (PVP) and the IR spectrum measured by photothermal spectroscopy matches the reference IR spectrum measured by an FTIR spectrometer. We further identify the organic surface coating of airborne TiO2 nanoparticles with a total mass of 4 pg. With an estimated detection limit of 44 fg, the presented sensor demonstrates a new paradigm in ultrasensitive vibrational spectroscopy for identification of airborne species.

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A portable x-ray fluorescence spectrometer equipped with a silicon drift detector (SDD) and a digital signal processor (DSP) was developed for in-field analysis of archeological samples at an excavation site. This spectrometer allows us to carry out highly sensitive analyses of various elements with atomic numbers down to Na in air by using two monochromatic x-ray sources obtained by doubly bent toroidal monochromators of graphite (0002) (Pd Ka for medium-heavy elements) and PET (200) (Pd La for light elements) and white x-rays with a Zr filter excited at 40 kV for heavy elements. The detection limit was 0.31% for Al and 4 ppm for Sr in a standard cement sample. The spectrometer was set in a room of the excavation laboratory at al-Tur Sinai in the Sinai Peninsula in Egypt in the summer of 2001. The Middle Eastern Culture Center has been conducting an excavation of the sites in al-Tur al-Kilani and Raya, which were important port cities of Red Sea trade from early Islamic periods: al-Tur (A.D.14-20) and Raya (A. D.8-12). The instrument was operated without any problems and 222 glass objects, 26 pottery sherds, seven pigments and 88 metallic objects were analyzed non-destructively during a 1 month stay. Since this was the first chemical analysis done at the sites, many important archaeological findings were obtained in the present study. Glass objects were successfully classified based on their chemical compositions. Characterization of stained (luster) glasses was conducted.

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