Espresso Science: Laser-Based Diamond Thin-Film Waveguide Sensors for the Quantification of Caffeine

Abstract

Diamond thin-film waveguides with a nanocrystalline diamond layer of approximately 20 μm thickness were used in the mid-infrared regime in combination with quantum cascade lasers to detect the IR signature of caffeine. The diamond thin-film waveguides were fundamentally characterized with respect to their morphological properties via AFM and SEM. Theoretical simulations confirmed the feasibility of using a larger sensing area of approximately 50 mm2 compared to conventionally used strip waveguides. A comprehensive and comparative analysis confirmed the performance of the diamond thin-film-waveguide-based sensing system vs data obtained via conventional attenuated total reflection Fourier transform infrared spectroscopy using a single-bounce diamond internal reflection element. Hence, the utility of innovative diamond thin-film-waveguide-based sensors coupled with quantum cascade laser light sources has been confirmed as an innovative analytical tool, which may be used in a wide range of application scenarios, ranging from environmental to medical sensing, taking advantage of the robustness and inertness of nanocrystalline diamond.

Graphene-enhanced quantum cascade laser infrared spectroscopy using diamond thin-film waveguides

“…While a more detailed analysis of all minor ingredients was not the aim of the present investigation, detailed investigation for the compounds, as in previous study has focused on additional components such as caffein using QCL-based IR-ATR spectroscopy. 40 Sucrose and glucose are apparently not interfering in the wavelength regime of interest between 1660 cm −1 and 1580 cm −1 , as evident from the RedBull 0 spectra (Fig. 3A) where the sample contains no sugars at all.…”

Thin-Film Waveguide Laser Spectroscopy: A Novel Platform for Bacterial Analysis

“…Diamond thin film waveguides with a surface area of 5 mm × 10 mm ( w × l ) have been shown to provide a higher sensitivity and more pronounced features compared to conventional IR-ATR spectroscopy . To test the feasibility of such TFWGs for studying live specimens, E. coli had been inoculated for 24 h and analyzed in parallel via TFWG and IR-ATR spectroscopy.…”

“…These waveguides consist of a GaAs wafer substrate, a 6 μm thick Al 0.2 Ga 0.8 As cladding layer, and a 6 μm thick GaAs core layer (i.e., the actual waveguiding layer). , Such waveguides had been already used for the analysis of environmental key-analytes such as chlorinated hydrocarbons or perchlorides. ,, While to date they had not been used for protein analysis, they are a promising tool for the label-free analysis of biomolecules such as proteins and DNA . Diamond TFGWs on the other hand have been already successfully used for sensing protein structures and living cells, being transparent in the MIR spectral range, providing exceptional chemical inertness and biocompatibility. , …”