A straightforward multi-scale infrared (IR) spectroscopic characterization of anisotropic polymer nanofibers for material research and biomedical applications is presented. Polarization dependent IR spectroscopies with spatial resolutions from a few mm down to a few 10 nm (by atomic force microscopy-based infrared spectroscopy, AFM-IR) and time resolutions from the min to µs range (by infrared dual-comb polarimetry, IR-DCP) are used. Compared to AFM-IR, which measures the absorption via the photothermal expansion, and IR ellipsometry, which measures amplitudes of sand p-polarized radiation and their phase differences, IR-DCP measures separately s-and p-polarized amplitudes and phases
Recent developments in infrared (IR) microfluidics for sensitive monitoring of molecular adsorption at solid–liquid interfaces are briefly reviewed. A microfluidic platform is presented that uses a metallic island film for surface enhanced IR absorption (SEIRA) coupled to IR spectroscopies for bio-sensing and vibrational investigations of molecular monolayers and their adsorption kinetics. Exemplarily, IR spectral monitoring of the monolayer formation of 4-mercaptobenzonitrile (4-MBN) in liquid environment is discussed as a Langmuir isotherm. Adsorption isotherms of specific molecular vibrations are analyzed from the time-dependent evolution of band amplitudes and peak areas during adsorption. Given the detection limit of 0.03 nmol/cm2 , the isotherms of 4-MBN, gluthathione (GSH) monolayer formation, and the sensing of 4-nitrobenzylmercaptan (4-NBM) by the MP/graphene surface are compared. Potential applications are bio- and bio-medical sensing as well as the study of processes, e. g., enzymatic reactions, chemical or catalytic reactions, receptor–ligand interactions, and structural changes of molecules due to environmental stimuli.
Advances in polarimetric techniques are of high interest in multiple scientific fields. Polarimetry characterizes optical and material properties such as anisotropy and structure, which relate to physical, chemical and functional properties of materials used in optoelectronic, polymer, plasmonic, bio-related and pharmaceutical applications. Laser-based infrared (IR) spectroscopic methods beyond classical Fourier-transform infrared (FTIR) spectroscopy enable previously impossible polarimetric investigations from macroscopic to nanoscopic length scales. This contribution focuses on new polarimetry techniques for detailed analyses of structural and material properties of thin films and surfaces. Specifically, we show applications of two laboratory-based instruments that employ tunable quantum cascade lasers (QCLs) from Daylight Solutions as brilliant light sources. Regarding far-field IR spectroscopic measurements, a novel laser ellipsometer (built in cooperation with Sentech Instruments) simultaneously measures spectral amplitude and phase information via single-shot detection of four different polarization states. The device reaches temporal resolutions in the μs to ms range at high spectral (< 0.5 cm−1 ) and lateral resolutions (≤ 125μm). At the nanoscale, photothermal atomic force microscopy (AFM)-IR (Anasys, Bruker), based on a QCL and a polarizing unit, enables polarimetry with lateral resolutions of a few 10 nm.
Ellipsometry and infrared polarized reflection spectroscopy at oblique incidence of golden split-ring resonators were simulated and discussed. The ellipsometric spectra were related to the reflection spectra for the two polarization of the incident wave, s- and p-, with electric field being normal and parallel to the plane of incidence, respectively. Near-field and bulk current distribution at the resonances proved that they correspond to the multiple plasmonic modes of the split-ring resonators. The calculated magnetic moment showed that at oblique incidence both magnetic and electric field induce the magnetic resonances.
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