Shining New Light on Old Principles: Localization of Evanescent Field Interactions at Infrared—Attenuated Total Reflection Sensing Interfaces

Abstract

A combined experimental and spectral ray tracing approach for identifying and evaluating evanescent field interactions with discrete surface deposits along a horizontal attenuated total reflection (HATR) element is presented. By experimentally depositing poly(styrene-co-butadiene) (PSCB) residues at fixed intervals along the measurement surface of a HATR crystal, distinct regions of evanescent field interaction with the surface deposits along the multi-reflection waveguide are visualized via infrared absorption features of PSCB. The infrared-attenuated total reflection (IR-ATR) measurements were confirmed by spectral ray tracing analysis simulating transmission-absorption spectra after modeling the polymeric surface deposits as thin-film IR absorbing cylinders. The presented analytical procedures and simulations provide a generic strategy for identifying and evaluating "active" sensing regions along ATR elements. Additionally, the simulated ATR setup along with the presented spectral ray tracing procedures provide a virtual platform aiding the development, optimization, and integration of deep-sea IR-ATR sensor probes with submersible mid-infrared spectrometers for in situ marine monitoring applications, which was the initial motivation for these studies.

Combining Scanning Electrochemical Microscopy with Infrared Attenuated Total Reflection Spectroscopy for in Situ Studies of Electrochemically Induced Processes

“…Hence, the resulting poly(SNS) films may have different thicknesses and different levels of polymerization yet during the same observation periods for the IR measurements. Furthermore, the IR measurement is subject to intensity variations across the ZnSe single bounce crystal surface in dependence of the area illuminated by the evanescent field 66. These factors are considered responsible for the fact that despite keeping the conditions for polymerizing each spot constant, variations in the IR signal are still observable.…”

Preparation of Laser-Ablated Ag Nanoparticle–MMT Clay-Based Beeswax Antibiofilm Coating

“…This approach allowed for simplifying the system, limiting bioactivity mechanisms only to the biofilm exposure towards metal ions. Previous studies showed the localization of IR-active sensing regions [64,69], helping to determine IR-inactive areas along the crystal surface; thus, we avoid infrared signals being convoluted with absorption intensity that might come from the composite film. The active spots were able to be attracted by the sampled biofilms as a consequence of exposure only to the Ag + ions released by the neighboring regions (3 mm spots of nanoantimicrobials, 0.5 mm thickness).…”

Nitrogen-doped diamond-like carbon as optically transparent electrode for infrared attenuated total reflection spectroelectrochemistry

“…The deposition of the titanium|gold strips at the top and bottom portions of the waveguide resulted in an additional minor attenuation of the optical throughput, as radiation is confined mostly in the central portion of the waveguide. 83 Hence, despite substantial modification of the waveguide surface its optical transparency remains sufficient for spectroelectrochemical experiments (Fig. 5).…”