With the availability of broadly tunable external cavity quantum cascade lasers (EC-QCLs), particularly bright mid-infrared (MIR; 3-20 μm) light sources are available offering high spectral brightness along with an analytically relevant spectral tuning range of >2 μm. Accurate isotope ratio determination of (12)CO2 and (13)CO2 in exhaled breath is of critical importance in the field of breath analysis, which may be addressed via measurements in the MIR spectral regime. Here, we combine for the first time an EC-QCL tunable across the (12)CO2/(13)CO2 spectral band with a miniaturized hollow waveguide gas cell for quantitatively determining the (12)CO2/(13)CO2 ratio within the exhaled breath of mice. Due to partially overlapping spectral features, these studies are augmented by appropriate multivariate data evaluation and calibration techniques based on partial least-squares regression along with optimized data preprocessing. Highly accurate determinations of the isotope ratio within breath samples collected from a mouse intensive care unit validated via hyphenated gas chromatography-mass spectrometry confirm the viability of IR-HWG-EC-QCL sensing techniques for isotope-selective exhaled breath analysis.

The monitoring of the emerging contaminant, microplastics, in the environment, in water supply, and for food safety is of major interest to science, consumers, and governments. While the chemical analysis of these particles is considered mandatory, a rapid and reliable method for the determination of particle sizes, shapes, and numbers is missing, as existing methods are not fitting into current laboratory measurement routines. In this study, we present an approach for circumventing these issues through the application of quantum cascade laser-based microscopy combined with an automated data analysis. This method allows the measurement of an area of 144 mm2 in 36 min, with a pixel resolution of 4.2 μm, which is an appropriate timeframe and spatial resolution for routine measurements. The performance was compared to the existing state-of-the-art Fourier transform infrared microscopy analyses. Further, the application of the method on various environmental samples was investigated to examine its capacity to provide number and variety of present particles. The described analytical procedure overcomes the last restrictions for schedulable and rapid microplastic monitoring, resulting in a highly detailed data set for particle numbers, particle shapes, and polymer types.

The performance and versatility of GaAs/AlGaAs thin-film waveguide technology in combination with quantum cascade lasers for mid-infrared spectroscopy in comparison to conventional FTIR spectroscopy is presented. Infrared radiation is provided by a quantum cascade laser (QCL) spectrometer comprising four tunable QCLs providing a wavelength range of 5-11 μm (1925-885 cm(-1)) within a single collimated beam. Epitaxially grown GaAs slab waveguides serve as optical transducer for tailored evanescent field absorption analysis. A modular waveguide mounting accessory specifically designed for on-chip thin-film GaAs waveguides is presented serving as a flexible analytical platform in lieu of conventional attenuated total reflection (ATR) crystals uniquely facilitating macroscopic handling and alignment of such microscopic waveguide structures in real-world application scenarios.

Polydopamine (PDA) has high potential in biorelevant applications as a versatile thin film material, e.g., as adhesive coating for cell immobilization or for sensing applications due to the plethora of functional groups. In this study we present the modification of conductive colloidal atomic force−scanning electrochemical microscopy (AFM-SECM) probes with electrochemically deposited PDA resulting in functional probes for quantitative electrochemical adhesion studies. Surface functionality of PDA can be altered by oxidation or reduction of functional groups applying an appropriate potential to the PDA-modified AFM-SECM probe, thereby enabling adhesion measurements under potential control. This facilitates probing specific interactions of surface groups present in PDA with various surfaces of different wettabilities. The versatility of such switchable AFM-SECM probes is demonstrated for electrochemical force spectroscopic studies at model samples such as plasma-treated gold substrates, hydrophobic or hydrophilic self-assembled monolayers, and for adhesion measurements of bacteria in dependence of altered surface charges of the colloidal probe. The maximum obtained adhesion force of a positively polarized PDA-modified AFM-SECM probe was 6.2 ± 2.2 nN, and it was about 50% less (i.e., 2.6 ± 1.1 nN) for a negatively polarized probe at a hydrophilic OHterminated gold surface. In situ control of the active surface groups enabled investigations on the influence of surface charges on adhesion. Furthermore, plateaus of constant force were observed, which are a characteristic of polymer structures. Finally, electrochemical force measurements with switchable probes were used for the first time during adhesion studies of bacterial cells (i.e., Pseudomonas f luorescens). Positively biased PDA-coated colloidal probes revealed adhesion forces of 6.0 ± 1.1 nN, whereas significantly reduced adhesion forces 1.1 ± 0.7 nN were observed for negatively biased PDA-modified colloidal probes.

Mycotoxins are toxic secondary metabolites of fungi that spoil food, and severely impact human health (e.g., causing cancer). Therefore, the rapid determination of mycotoxin contamination including deoxynivalenol and aflatoxin B1 in food and feed samples is of prime interest for commodity importers and processors. While chromatography-based techniques are well established in laboratory environments, only very few (i.e., mostly immunochemical) techniques exist enabling direct on-site analysis for traders and manufacturers. In this study, we present MYCOSPEC - an innovative approach for spectroscopic mycotoxin contamination analysis at EU regulatory limits for the first time utilizing mid-infrared tunable quantum cascade laser (QCL) spectroscopy. This analysis technique facilitates on-site mycotoxin analysis by combining QCL technology with GaAs/AlGaAs thin-film waveguides. Multivariate data mining strategies (i.e., principal component analysis) enabled the classification of deoxynivalenol-contaminated maize and wheat samples, and of aflatoxin B1 affected peanuts at EU regulatory limits of 1250 μg kg−1 and 8 μg kg−1, respectively.