Planar Silver Halide Research Articles

High-sensitivity infrared attenuated total reflectance sensors for in situ multicomponent detection of volatile organic compounds in water.

In situ detection of volatile organic compounds (VOCs) in aqueous environments is imperative for ensuring the quality and safety of water supplies, yet it remains a challenging analytical task. We present a high-sensitivity method for in situ analysis of multicomponent VOCs at low concentrations based on the use of infrared attenuated total reflection (IR-ATR) spectroscopy. This protocol uses a unique ATR waveguide, which comprises a planar silver halide (AgCl(x)Br(1-x)) fiber with cylindrical extensions at both ends to increase the number of internal reflections, and a polymer coating that traps VOCs and excludes water molecules. Depending on the type of VOC and measurement scenario, IR spectra with specific frequency windows, scan times and spectral resolutions are obtained, from which concentration information is derived. This protocol allows simultaneous detection of multiple VOCs at concentrations around 10 p.p.b., and it enables accurate quantification via a single measurement within 5 min without the need for sample collection or sample pretreatment. This IR-ATR sensor technology will be useful for other applications; we have included a procedure for the analysis of protein conformation changes in Supplementary Methods as an example.

Probing the secondary structure of bovine serum albumin during heat-induced denaturation using mid-infrared fiberoptic sensors.

Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy using a special waveguide based on a silver halide fiber was used for probing the heat-induced secondary structure and conformation changes of bovine serum albumin (BSA). From the secondary derivative and the curve fitting of the obtained ATR-FTIR spectra, the changes of the BSA secondary structure with temperature were clearly identified. Two different thermal denaturation temperature ranges (i.e., 50-52 and 80-82 °C, at which a change of the protein structure occurred) were determined, while only one denaturation temperature was previously identified via classical FTIR measurements. Additionally, taking advantage of two-dimensional correlation spectroscopy more detailed information on changes of the protein secondary structure was revealed. The developed method facilitates in situ, sensitive, and more in-depth probing of protein secondary structures, which represents a significant advancement compared to conventional characterization methods.

Mid-Infrared Planar Silver Halide Waveguides with Integrated Grating Couplers

Grating couplers for planar silver halide waveguides were designed and fabricated by using focused ion beam (FIB) milling technology, facilitating coupling of mid-infrared radiation from quantum cascade lasers into thin-film waveguide structures. An optimized rectangular grating structure for an emitted wavelength of 10.4 μm, with a grating constant of 16.4 μm was integrated into a silver halide waveguide substrate via an optimized FIB fabrication procedure. Efficient incoupling and radiation propagation through the waveguide was confirmed by analyzing droplets of acetic acid at different concentrations, deposited at the waveguide surface via evanescent field absorption spectroscopy.

IR‐ATR Chemical Sensors Based on Planar Silver Halide Waveguides Coated with an Ethylene/Propylene Copolymer for Detection of Multiple Organic Contaminants in Water

Der Nachweis monocyclischer aromatischer Kohlenwasserstoffe, z. B. p-, m-, o-Xylol, Toluol und Benzol (1–5), gelang in einer Messung, wobei ein planarer IR-ATR-faseroptischer Sensor verwendet wurde, der mit Ethylen/Propylen-Copolymer beschichtet war (ATR=abgeschwächte Totalreflexion). Verglichen mit herkömmlichen IR-Methoden hat das System einen großen dynamischen Nachweisbereich.

IR‐ATR Chemical Sensors Based on Planar Silver Halide Waveguides Coated with an Ethylene/Propylene Copolymer for Detection of Multiple Organic Contaminants in Water

IR‐ATR Chemical Sensors Based on Planar Silver Halide Waveguides Coated with an Ethylene/Propylene Copolymer for Detection of Multiple Organic Contaminants in Water

Ultra-sensitive mid-infrared evanescent field sensors combining thin-film strip waveguides with quantum cascade lasers

We demonstrate ultra-sensitive chemical sensing in the mid-infrared spectral regime with a combination of quantum cascade lasers (QCLs) with GaAs/Al(0.2)Ga(0.8)As strip waveguides fabricated via metal-organic vapor-phase epitaxy (MOVPE) and reactive ion etching (RIE) using evanescent field absorption spectroscopy. These strip waveguides have been designed with a width of 200 μm, thereby facilitating 2-D confinement and mode-matched propagation of mid-infrared radiation emitted from a distributed feedback (DFB) QCL at a wavelength of 10.3 μm. Acetic anhydride was detected with a limit of detection (LOD) of 18 pL (19.4 ng) deposited at the waveguide surface by overlapping of the vibrational absorption of the methyl group with the emission frequency of the QCL. The obtained results indicate a remarkable enhancement in sensitivity by three orders of magnitude compared to previously reported multimode planar silver halide waveguides. Further reduction of the waveguide strip width to 50 μm resulted in an additional sensitivity enhancement yielding a calculated LOD of 0.05 pL for the exemplary analyte acetic anhydride, which is among the most sensitive evanescent field absorption measurements with a miniaturized mid-infrared sensor system reported to date.

Thin film infrared spectroscopy on planar silver halide: a new technology for water and other liquids in the mesoscopic domain

The essentially unexplored phenomenon of electrostriction on polar solids is now exploited to restrict the motion of polar liquids in infrared spectroscopic experiments. We have found a wide variety of water oligomers for which theoretical properties had previously been calculated utilizing a recently developed cell for thin film infrared spectroscopy. Short acquisition times (to detect transient species) and low signal energies (less disruption of transient species) on planar silver halide (many reflections, limited penetration depth (therefore, small sample size), restraint of molecular motion by electrostriction (thus making possible capture of transient spectra)) were utilized to yield heretofore unknown spectroscopic properties of water. The results included identification of five oligomers (cyclic hexamers (chair, boat), cyclic pentamer and bicyclic books (1, 2)). The new technique of lifetime tagging was used to track these species, leading to the selection of marker peaks for specific oligomers. Each oligomer possessed groups of peaks in the symmetric OH stretching region, for which a new type of model, isomotomers, supported its identification. Intramolecular H-bonding in books 1 and 2 provided extra support for the assignments. Other polar liquids (N-methylformamide, dichloromethane) are briefly discussed. The tetrahedral character of water appears to result from an average over many linear oligomers.

Molecule-Enhanced Surface-Enhanced Infrared Absorption Spectroscopy (MOSEIRA)

Surface-enhanced infrared absorption spectroscopy (SEIRA) of methanol, ethanol, 1-propanol, and 2-propanol in thin films on planar silver halide (AgX) fibers under slow N(2) flow using 1 sec scans reveals structure in absorbance-time plots. The absorption intensities show extra enhancements (3x) in the absorbance (O--H stretch) ascribed to oligomers present at the AgX surface (molecule enhanced, thus MOSEIRA). This is above those due to amplification (40x, 20 reflections) and enhancement (30x, image dipoles or surface phonon polaritons). In the case of ethanol an excellent initial pentamer spectrum evolves over 8-10 min to a mixture of pentamer, tetramer, and trimer spectra that within another minute forms small oligomers and monomers. We use a new type of cell for infrared spectroscopy containing an AgX planar fiber. The optical configuration leads to a vicinal region at the surface defined by evanescent waves. Within this region are surface-induced organized species such as ethanol oligomers. The planar AgX fiber supports 20 reflections and transmits light over a wide visible-infrared wavelength range. Short scan times permit the study of volatile substrates or solvents, including the effects of solvent polarity.

Fabrication and Characterization of Molecular Beam Epitaxy Grown Thin-Film GaAs Waveguides for Mid-Infrared Evanescent Field Chemical Sensing

Thin-film GaAs waveguides were designed and fabricated by molecular beam epitaxy for use in mid-infrared (MIR) evanescent field liquid sensing. Waveguides were designed to facilitate the propagation of a single mode at a wavelength of 10.3 microm emitted from a distributed feedback quantum cascade laser, which overlaps with molecular selective absorption features of acetic anhydride. The characterization of the waveguides shows transmission across a broad MIR band. Evanescent field absorption measurements indicate a significant sensitivity enhancement in contrast to multimode planar silver halide waveguides.

Infrared Evanescent Field Sensing with Quantum Cascade Lasers and Planar Silver Halide Waveguides

We demonstrate the first midinfrared evanescent field absorption measurements with an InGaAs/AlInAs/InP distributed feedback (DFB) quantum cascade laser (QCL) light source operated at room temperature coupled to a free-standing, thin-film, planar, silver halide waveguide. Two different analytes, each matched to the emission frequency of a QCL, were investigated to verify the potential of this technique. The emission of a 1650 cm(-1) QCL overlaps with the amide absorption band of urea, which was deposited from methanol solution, forming urea crystals at the waveguide surface after solvent evaporation. Solid urea was detected down to 80.7 microg of precipitate at the waveguide surface. The emission frequency of a 974 cm(-1) QCL overlaps with the CH3-C absorption feature of acetic anhydride. Solutions of acetic anhydride in acetonitrile have been detected down to a volume of 0.01 microL (10.8 microg) of acetic anhydride solution after deposition at the planar waveguide (PWG) surface. Free-standing, thin-film, planar, silver halide waveguides were produced by press-tapering heated, cylindrical, silver halide fiber segments to create waveguides with a thickness of 300-190 microm, a width of 3 mm, and a length of 35 mm. In addition, Fourier transform infrared (FT-IR) evanescent field absorption measurements with planar silver halide waveguides and transmission absorption QCL measurements verify the obtained results.

Surface-Enhanced Infrared Absorption and Amplified Spectra on Planar Silver Halide Fiber

We have discovered surface-enhanced infrared absorption (SEIRA) on a planar silver halide surface, the first time this effect has been observed on a nonmetallic substrate. The enhancement is not du...

Surface-Enhanced Infrared Absorption of p-Nitrobenzoic Acid on Planar Silver Halide Fiber

Surface-enhanced infrared absorption (SEIRA), recently discovered for trypsin on a planar silver halide surface, is now demonstrated for the small organic molecule, p-nitrobenzoic acid (pNBA). Evaporation of pNBA solutions in acetonitrile yields the acid dimer (confirmed by the unique IR signature of carboxylic acid dimers). The absorption changes for pNBA with quantity exhibit two regimes: “enhanced” and “regular”. A plot of absorbance versus quantity reveals how SEIRA changes with distance from the surface. The surface orientation of pNBA has the long and short axes (unit cell) parallel to the surface (packing density/carbonyl peaks). “Slice” spectra differentiate between surface pNBA and other layers. Most of the numerous previous reports on pNBA actually refer to the p-nitrobenzoate anion probably generated through reaction of surface silver oxide with the acid.