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In this article, we demonstrate a promising inline near-infrared measurement scheme for 24/7 biofilm monitoring based on cost-effective microelectromechanical system-based spectrometer technology. The shown near-infrared spectral data, acquired at a beer-canning line during a representative time span of 10 days, are analyzed by means of principal component analysis and the performance of the monitoring system and its capability to identify biofilms on its sensor surface are investigated by comparing spectral response with results of offline polymerase chain reaction measurements of smear samples. Correlations between presence of a biofilm and its thickness with scores on PC1 and PC2, respectively, were observed.

We have monitored the evolution of the optical properties of ultrathin N,N′-dipentylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C5) molecular thin films during their growth on muscovite mica surfaces using differential reflectance spectroscopy (DRS) and fluorescence spectroscopy (FL). In the monolayer regime, the DRS shows a monomer-like absorption, whereas the FL reveals a transition from monomeric to excimer-like emission accompanied by a quenching of the intensity with the increase of coverage. The observed evolution of the FL signals can be explained by a two dimensional (2D) gas to condensed phase transition. The characteristic fluorescence of the condensed phase implies an enhancement of the intermolecular coupling and the opening of new channels for the relaxation of the excited state. The π–π stacking, which is manifested by both DR and FL spectroscopies, emergences only after the completion of the first monolayer. Finally, by analyzing the variation of the fluorescence spectrum, we have revealed the dewetting of the uncompleted PTCDI-C5 monolayer upon air exposure. This observation has been verified by atomic force microscopy (AFM).

In this work, the findings of an in situ fluorescence spectroscopy and microscopy investigation of the growth of $\ensuremath{\alpha}$-sexithiophene ($\ensuremath{\alpha}\text{\ensuremath{-}}6\mathrm{T}$) thin films on muscovite mica are presented. The sensitive dependence of the fluorescence emission on the molecular arrangement is exploited to reveal the details of the $\ensuremath{\alpha}\text{\ensuremath{-}}6\mathrm{T}$ thin film growth from the initial stage. A Stranski-Krastanov growth mode with a two-monolayer-thick wetting layer is observed. The molecules within the wetting layer lie flat on the mica surface and their molecular arrangement evolves as a function of the surface coverage. After the completion of the wetting layer, needlelike three-dimensional islands consisting of flat-lying molecules and flat islands containing nearly-upright-standing molecules grow competitively. Exposing the $\ensuremath{\alpha}\text{\ensuremath{-}}6\mathrm{T}$ thin films to air leads to dewetting and this process is found to be partially reversible, i.e., a large fraction of the wetting layer recovers gradually after the sample is transferred back into vacuum. This dewetting (rewetting) process is attributed to the surface modification due to the adsorption (desorption) of water molecules.

In this work, mid-infrared hyperspectral images of multilayer polymer film (MLPF) cross sections are acquired with a high-speed quantum cascade laser (QCL) based mid-infrared microscope and analyzed using different data analysis techniques. The investigated MLPF is a polypropylene (PP) and ethylene-vinyl alcohol co-polymer (EVOH) composite commonly used for food packaging due to its outstanding barrier characteristics. Pure band integration of supposedly selective absorption bands for the two constituents of the MLPF is compared to principal component analysis (PCA) and multivariate curve resolution (MCR) algorithms regarding the ability to spatially resolve the differently composed areas in the MLPF. While both pure band integration and PCA are strongly affected by common physical artifacts in the spectral data, such as sample tilt, scattering or interference effects, MCR managed to give a clear picture of the composition of the MLPF, which matches the actual situation given by the manufacturing process. The obtained results can guide the way to the application of high-performance mid-infrared spectroscopic instrumentation for spatially resolved polymer analysis by meaningful interpretation of hyperspectral image data.

Real-time measurements and adjustments of critical process parameters are essential for the precise control of fermentation processes and thus for increasing both quality and yield of the desired product. However, the measurement of some crucial process parameters such as biomass, product, and product precursor concentrations usually requires time-consuming offline laboratory analysis. In this work, we demonstrate the in-line monitoring of biomass, penicillin (PEN), and phenoxyacetic acid (POX) in a Penicillium chrysogenum fed-batch fermentation process using low-cost microspectrometer technology operating in the near-infrared (NIR). In particular, NIR reflection spectra were taken directly through the glass wall of the bioreactor, which eliminates the need for an expensive NIR immersion probe. Furthermore, the risk of contaminations in the reactor is significantly reduced, as no direct contact with the investigated medium is required. NIR spectra were acquired using two sensor modules covering the spectral ranges 1350–1650 nm and 1550–1950 nm. Based on offline reference analytics, partial least squares (PLS) regression models were established for biomass, PEN, and POX either using data from both sensors separately or jointly. The established PLS models were tested on an independent validation fed-batch experiment. Root mean squared errors of prediction (RMSEP) were 1.61 g/L, 1.66 g/L, and 0.67 g/L for biomass, PEN, and POX, respectively, which can be considered an acceptable accuracy comparable with previously published results using standard process spectrometers with immersion probes. Altogether, the presented results underpin the potential of low-cost microspectrometer technology in real-time bioprocess monitoring applications © 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Chemical mapping was demonstrated with a mid-infrared (MIR) microspectroscopy setup based on a supercontinuum source (SC) emitting in the spectral range from 1.55 to 4.5 µm and a MEMS-based Fabry-Perot filter spectrometer. Diffraction limited spatial resolution in reflection geometry was achieved. A multilayer film consisting of different polymers and mixtures thereof was measured and results were compared to those gained with a conventional FTIR microscope equipped with a thermal MIR source. Results show that compared to thermal sources, the application of the SC source results in higher signal-to-noise ratios together with better spatial resolution and faster scanning. Furthermore, diffraction limited imaging of red blood cells was demonstrated for the first time in the MIR spectral region in reflection mode. The distinctive characteristics of the MIR spectral region in conjunction with the high brightness, spatial coherence and broadband nature of supercontinuum radiation show the potential for improving infrared microscopy significantly.

Laser-based infrared spectroscopic ellipsometry (SE) is demonstrated for the first time, to the best of our knowledge, by applying a tunable quantum cascade laser (QCL) as a mid-infrared light source. The fast tunability of the employed QCL, combined with phase-modulated polarization, enabled the acquisition of broadband (900–1204 cm−1), high-resolution (1 cm−1) ellipsometry spectra in less than 1 second. A comparison to a conventional Fourier-transform spectrometer-based IR ellipsometer resulted in an improved signal-to-noise ratio (SNR) by a factor of at least 290. The ellipsometry setup was finally applied for the real-time monitoring of molecular reorientation during the stretching process of an anisotropic polypropylene film, thereby illustrating the advantage of sub-second time resolution. The developed method exceeds existing instrumentation by its fast acquisition and high SNR, which could open up a set of new applications of SE such as ellipsometric inline process monitoring and quality control.