Surface Functionalization with Polymer Membrane or SEIRA Interface to Improve the Sensitivity of Chalcogenide-Based Infrared Sensors Dedicated to the Detection of Organic Molecules

Abstract

Priority substances likely to pollute water can be characterized by mid-infrared spectroscopy based on their specific absorption spectral signature. In this work, the detection of volatile aromatic molecules in the aqueous phase by evanescent-wave spectroscopy has been optimized to improve the detection efficiency of future in situ optical sensors based on chalcogenide waveguides. To this end, a hydrophobic polymer was deposited on the surface of a zinc selenide prism using drop and spin-coating methods. To ensure that the water absorption bands will be properly attenuated for the selenide waveguides, two polymers were selected and compared: polyisobutylene and ethylene/propylene copolymer coating. The system was tested with benzene, toluene, and ortho-, meta-, and para-xylenes at concentrations ranging from 10 ppb to 40 ppm, and the measured detection limit was determined to be equal to 250 ppb under these analytical conditions using ATR-FTIR. The polyisobutylene membrane is promising for pollutant detection in real waters due to the reproducibility of its deposition on selenide materials, the ease of regeneration, the short response time, and the low ppb detection limit, which could be achieved with the infrared photonic microsensor based on chalcogenide materials. To improve the sensitivity of future infrared microsensors, the use of metallic nanostructures on the surface of chalcogenide waveguides appears to be a relevant way, thanks to the plasmon resonance phenomena. Thus, in addition to preliminary surface-enhanced infrared absorption tests using these materials and a functionalization via a self-assembled monolayer of 4-nitrothiophenol, heterostructures combining gold nanoparticles/chalcogenide waveguides have been successfully fabricated with the aim of proposing a SEIRA microsensor device.

Fluorescent Hydrophobic Test Strips with Sterically Integrated Molecular Rotors for the Detection of Hydrocarbons in Water and Soil with an Embedded Optical Read-Out

“…In comparison to the existing methods of oil sensing in water and soil, the method developed here is readily portable and cost-effective, which is not the case for most currently reported techniques. − Moreover, an electrochemical sensor reported by Dai et al for oil monitoring in water did not show sufficient robustness in field tests . Only two colorimetric and fluorescent sensors are comparable to the approach reported here in terms of cost and portability.…”

“…8 Certified methods such as gravimetric analysis 9 or gas chromatography with flame ionization detection 10 for laboratory detection of total petroleum hydrocarbons (TPHs) require an extraction step into a non-polar solvent and a subsequent analysis. The direct analytical methods found in the literature are based on infrared detection, 11 direct spectrophotometric 12 or fluorometric detection, 13 nuclear magnetic resonance spectroscopy, 14 or photoacoustics. 15 Unfortunately, these methods have some disadvantages such as high cost, the need for laboratory equipment and highly qualified personnel, lack of sensitivity, or detection of polyaromatic hydrocarbons only.…”

Surface enhanced infrared absorption mechanism and modification of the plasmonic response

“…This is even clearer for the Fano line shape when the resonance frequencies of the plasmonic system and of the molecules do not coincide (see later). We then prefer the term sensibility that we define by the difference between the extrema of the differential cross-section, divided by the maximum absorption cross-section of the isolated molecules, following [3]. In the example above, the sensibility is 6.54 × 10 5 .…”

“…Vibrational spectroscopies are powerful optical characterization techniques that offer the advantages of being label-free and non-destructive. In addition to Raman spectroscopy, infrared (IR) absorption is widely used for direct analysis of molecular functional groups and in situ analysis of surface reactions [1][2][3][4][5][6][7]. However, its small absorption cross-section, although much larger than that of Raman spectroscopy, limits its utility for large quantities of materials.…”

Spectroelectrochemical determination of thiolate self-assembled monolayer adsorptive stability in aqueous and non-aqueous electrolytes

“…4-PySH was chosen due to its extensive use and characterization in electrochemical literature. 32,[44][45][46][47] 4-MA and 4-NTP were utilized due to their similar structure and unique IR signals stemming from their amine [48][49][50] and nitro [51][52][53][54][55] group, respectively. 2-MBT was utilized to act as a control to validate how universal the determined SPWs are for other aromatic SAMs with differing structures, adsorption methods, and surface coverage.…”