Bottom-Illuminated Photothermal Nanoscale Chemical Imaging with a Flat Silicon ATR in Air and Liquid

We demonstrate a novel approach for bottom-illuminated atomic force microscopy and infrared spectroscopy (AFM-IR). Bottom-illuminated AFM-IR for measurements in liquids makes use of an attenuated total reflection setup where the developing evanescent wave is responsible for photothermal excitation of the sample of interest. Conventional bottom-illuminated measurements are conducted using high-refractive-index prisms. We showcase the advancement of instrumentation through the introduction of flat silicon substrates as replacements for prisms. We illustrate the feasibility of this technique for bottom-illuminated AFM-IR in both air and liquid. We also show how modern rapid prototyping technologies enable commercial AFM-IR instrumentation to accept these new substrates. This new approach paves the way for a wide range of experiments since virtually any established protocol for Si surface functionalization can be applied to this sample carrier. Furthermore, the low unit cost enables the rapid iteration of experiments

Method for Time-Resolved Monitoring of a Solid State Biological Film Using Photothermal Infrared Nanoscopy on the Example of Poly‑l‑lysine

We report time-resolved photothermal infrared nanoscopy measurements across a spectral range of more than 100 cm^–1 (1565 cm^–1 to 1729 cm^–1) at nanoscale spatial resolution. This is achieved through a custom-built system using broadly tunable external cavity quantum cascade lasers in combination with a commercially available atomic force microscope. The new system is applied to the analysis of conformational changes of a polypeptide (poly-l-lysine) film upon temperature-induced changes of the humidity in the film. Changes of the secondary structure from β-sheet to α-helix could be monitored at a time resolution of 15 s per spectrum. The time-resolved spectra are well comparable to reference measurements acquired with conventional Fourier transform infrared microscopy

Dual-Beam Photothermal Spectroscopy Employing a Mach–Zehnder Interferometer and an External Cavity Quantum Cascade Laser for Detection of Water Traces in Organic Solvents

We report on a mid-infrared (mid-IR) photothermal spectrometer for liquid-phase samples for the detection of water in organic solvents, such as ethanol or chloroform, and in complex mixtures, such as jet fuel. The spectrometer is based on a Mach–Zehnder interferometer (MZI) employing a He-Ne laser, a mini-flow cell with two embedded channels placed in the interferometer’s arms, and a tunable external cavity quantum cascade laser (EC-QCL) for selective analyte excitation in a collinear arrangement. In this study, the bending vibration of water in the spectral range 1565–1725 cm–1 is targeted. The interferometer is locked to its quadrature point (QP) for most stable and automated operation. It provides a linear response with respect to the water content in the studied solvents and photothermal analyte spectra, which are in good agreement with FTIR absorbance spectra. The method is calibrated and validated against coulometric Karl Fischer (KF) titration, showing comparable performance and sensitivity. Limits of detection (LODs) for water detection in the single-digit ppm range were obtained for chloroform and jet fuel due to their low background absorption, whereas lower sensitivity has been observed for water detection in ethanol due to pronounced background absorption from the solvent. In contrast to KF titration, which requires toxic reagents and produces waste, the developed method works reagent-free. It can be applied in an online format in the chemical industry as well as for fuel quality control, being industrial applications where traces of water need to be accurately determined, preferably in real-time. It thus holds great promise as a green alternative to the offline KF titration method, which is the current standard method for this application

Nitrogen-rich Compounds of the Actinoids: Dioxouranium(VI) 5,5′-Azobis[tetrazolide] Pentahydrate and Its Unusually Small Uranyl Angle

Uranyl­(VI) 5,5′-azobis­[tetrazolide] pentahydrate was synthesized and characterized using X-ray crystallography, elemental analysis, UV/vis, MIR, FIR, and Raman spectroscopy. It is the second-most nitrogen rich compound of uranium (26.72 wt % N) and only the second structurally characterized uranium complex with a tetrazole ligand described in the literature. The compound’s structure is characterized by an exceptionally small uranyl angle of 172.4(1)°, which provides information on the coordination properties of tetrazole ligands as they affect the donor’s environment by strong steric and perhaps electrostatic repulsion. The compound showed luminescence under excitation with a near UV laser. The mean lifetime of its excited state was shorter than in the case of UO₂(NO₃)₂·6H₂O, indicating quenching by the ligand. Despite its high nitrogen content (and thus potentially explosive character), the title compound proved to be stable even under neutron radiation causing induced fission processes

Quasi-Simultaneous In-Line Flue Gas Monitoring of NO and NO₂ Emissions at a Caloric Power Plant Employing Mid-IR Laser Spectroscopy

Two pulsed thermoelectrically cooled mid-infrared distributed feedback quantum cascade lasers (QCLs) were used for the quasi-simultaneous in-line determination of NO and NO₂ at the caloric power plant Dürnrohr (Austria). The QCL beams were combined using a bifurcated hollow fiber, sent through the flue tube (inside diameter: 5.5 m), reflected by a retro-reflector and recorded using a fast thermoelectrically cooled mercury–cadmium–telluride detector. The thermal chirp during 300 ns pulses was about 1.2 cm^–1 and allowed scanning of rotational vibrational doublets of the analytes. On the basis of the thermal chirp and the temporal resolution of data acquisition, a spectral resolution of approximately 0.02 cm^–1 was achieved. The recorded rotational vibrational absorption lines were centered at 1900 cm^–1 for NO and 1630 cm^–1 for NO₂. Despite water content in the range of 152–235 g/m³ and an average particle load of 15.8 mg/m³ in the flue gas, in-line measurements were possible achieving limits of detection of 73 ppb for NO and 91 ppb for NO₂ while optimizing for a single analyte. Quasi-simultaneous measurements resulted in limits of detection of 219 ppb for NO and 164 ppb for NO₂, respectively. Influences of temperature and pressure on the data evaluation are discussed, and results are compared to an established reference method based on the extractive measurements presented

Additional file 1: of Phosphonate coating of SiO2 nanoparticles abrogates inflammatory effects and local changes of the lipid composition in the rat lung: a complementary bioimaging study

Figure S1. Effect of different SiO2 NP on lung histology. Figure S2. MALDI-MS/MS spectrum resulting from the fragmentation of precursor m/z 721.4. Figure S3. MALDI-MS/MS spectrum resulting from the fragmentation of precursor m/z 861.5. Figure S4. Ion images from a vehicle-treated control lung. Figure S5. Ion images from a SiO2-p-treated control lung. (DOCX 1889 kb

Remote Sensing with Commutable Monolithic Laser and Detector

The ubiquitous trend toward miniaturized sensing systems demands novel concepts for compact and versatile spectroscopic tools. Conventional optical sensing setups include a light source, an analyte interaction region, and a separate external detector. We present a compact sensor providing room-temperature operation of monolithic surface-active lasers and detectors integrated on the same chip. The differentiation between emitter and detector is eliminated, which enables mutual commutation. Proof-of-principle gas measurements with a limit of detection below 400 ppm are demonstrated. This concept enables a crucial miniaturization of sensing devices