The analytical and physical properties are reported for nanohole arrays prepared with glancing angle deposition (GLAD) or plasma treatment of a nanosphere lithography (NSL) mask prior to the deposition of a thin Au film. The nanohole arrays obtained with a 450 nm nanospheres mask are characterized using atomic force microscopy (AFM) to determine the depth and the width of the nanoholes, and the periodicity of the nanohole arrays. The analytical properties are reported in terms of the surface plasmon (SP) excitation wavelength (500 nm to 1000 nm), sensitivity to refractive index (27 nm RIU(-1) to 487 nm RIU(-1)), sensitivity to monolayer formation (shift of the SP band by approx. 1 nm), and refractive index resolution (10(-4) RIU). These simple techniques produce well-ordered nanohole arrays with tunable analytical and physical properties for the development of biosensors.

Simultaneous and molecularly selective parts-per-billion detection of benzene, toluene, and xylenes (BTX) using a thermal desorption (TD)-FTIR hollow waveguide (HWG) trace gas sensor is demonstrated here for the first time combining laboratory calibration with real-world sample analysis in field. A calibration range of 100-1000 ppb analyte/N(2) was developed and applied for predicting the concentration of blinded environmental air samples within the same concentration range, and demonstrate close agreement with the validation method used here, GC-FID. The analyte concentration prediction capability of the TD-FTIR-HWG trace gas sensor also compares well with the industrial standard and other experimental techniques including GC-PID, ultrafast GC-FID, and GC-DMS, which were simultaneously operated in the field. With the advent of a quantum cascade laser with emission frequencies specifically tailored to efficiently overlap benzene absorption as the most relevant analyte, the overall sensor footprint could be considerably reduced to ultimately yield hand-held trace gas sensors facilitating direct and real-time detection of BTX in air down to low ppb levels.

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A hollow core optical fiber gas sensor has been developed in combination with a Fourier transform infrared (FT-IR) spectrometer operating in the spectral range of 4000-500 cm(-1), enabling continuous detection of small volume gas-phase analytes such as CH(4), CO(2), C(2)H(5)Cl, or their mixtures at trace levels. Ag/Ag-halide hollow core optical fibers simultaneously serve as an optical waveguide for broad-band mid-infrared radiation and as a miniaturized absorption gas cell. Specifically, carbon dioxide, methane, and ethyl chloride as well as binary mixtures in a carrier gas were analyzed during exponential dilution experiments. In the studies reported here, the integration of an optical gas sensor with FT-IR spectroscopy provides excellent detection limits for small gas volumes ( approximately 1.5 mL) of individual analytes at a few tens of parts per billion (ppb, vol/vol) for carbon dioxide and a few hundreds of ppb (vol/vol) for methane. Furthermore, the broad-band nature of the radiation source and of the hollow core optical waveguide provides the capability of multi-constituent analysis in mixtures.