Gas analysis via mid-infrared (MIR) spectroscopic techniques has gained significance due to its inherent molecular selectivity and sensitivity probing pronounced vibrational, rotational, and roto-vibrational modes. In addition, MIR gas sensors are suitable for real-time monitoring in a wide variety of sensing scenarios. Our research team has recently introduced so-called substrate-integrated hollow waveguides (iHWGs) fabricated by precision milling, which have been demonstrated to be useful in online process monitoring, environmental sensing, and exhaled breath analysis especially if low sample volumes (i.e., few hundreds of microliters) are probed with rapid signal transients. A logical next step is to establish ultralightweight, potentially disposable, and low-cost substrate-integrated hollow waveguides, which may be readily customized and tailored to specific applications using 3D printing techniques. 3D printing provides access to an unprecedented variety of thermoplastic materials including biocompatible polylactides, readily etchable styrene copolymers, and magnetic or conductive materials. Thus, the properties of the waveguide may be adapted to suit its designated application, e.g., drone-mounted ultralightweight waveguides for environmental monitoring or biocompatible disposable sensor interfaces in medical/clinical applications.Keywords: 3D printing; breath diagnostics; iHWG; mid-infrared; polyHWG; polymer-based hollow waveguide; quantum cascade laser; substrate-integrated hollow waveguide;

Well-characterized silane layers are essential for optimized attachment of (bio)molecules enabling reliable chem/biosensor performance. Herein, binding properties and orientation of 3-mercaptopropyltrimethoxysilane layers at crystalline sapphire (0001) surfaces were determined by water contact angle measurements, infrared reflection absorption spectroscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Infrared reflection absorption spectroscopy measurements suggest an almost perpendicular arrangement of the MPTMS molecules to the substrate surface. Adhesion force studies between a silicon nitride AFM tip and modified sapphire, gold, and silicon dioxide substrates were investigated by peak force tapping atomic force microscopy and used to define the silane binding properties on these surfaces. As expected, the Al–O–Si bond was determined to be responsible for the layer formation at the sapphire substrate surface.Keywords: atomic force microscopy; binding properties; infrared reflection absorption spectroscopy; sapphire; self-assembled layers; X-ray photoelectron spectroscopy;

Molecularly imprinted polymers (MIPs) with a core–shell structure for efficient, reliable, and selective extraction of vanillin via solid-phase extraction (SPE) and incubation methods were developed using a sol–gel process based on (3-aminopropyl)triethoxysilane (APTES) as the functional monomer, tetraethoxysilane (TEOS) as the cross-linker, and vanillin as the template. An inorganic core composed of porous (SM1) and non-porous (SM2) silica microspheres was prepared by co-condensation of TEOS and (3-aminopropyl)trimethoxysilane (APTMS) in a water-in-oil (W/O) macroemulsion. The thus synthesized materials were characterized in detail, and their molecular recognition properties and selectivity were demonstrated by evaluating their adsorption capacity and binding kinetics at imprinted (MIP) and non-imprinted (NIP) control materials. The proposed binding mechanism takes advantage of the amino groups associated with APTES interacting with the functional groups of the template molecules to form hydrogen-bonded complexes. Furthermore, synthesis conditions were optimized such that the imprinting efficiency and adsorption capacity were maximized. Finally, it was demonstrated via incubation experiments that the thus generated MIP core–shell hybrid microspheres provide rapid adsorption with high binding capacities (up to 5.64 mg g−1), excellent imprinting factors (IF up to 2.37), and exceptional reusability (reused >20 times).

•Signal enhancement from two analytes at plasmonic nanostars and nanospheres were compared for SEIRAS in IR-ATR.•The signal obtained from nanostars was at least 2-times higher in comparison with nanospheres.•Up to 10-times signal enhancement at plasmonic nanostars for SEIRAS was observed.•Dependence of enhancement on the number of nanostars at the internal reflection element surface was demonstrated.•SEIRA signal was correlated to the concentration of analyte molecules present within the evanescent field.Plasmonic anisotropic nanoparticles possess a number of hot spots on their surface due to the presence of sharp edges, tips or vertices, leading to a high electric field strength surrounding the nanostructures. In this paper, we explore different plasmonic nanostructures, including anisotropic gold nanostars (AuNSts) and spherical gold nanoparticles, in surface-enhanced infrared absorption spectroscopy (SEIRAS) in an attenuated total reflection (ATR) configuration. In our experiments, we observed up to 10-times enhancement of the infrared (IR) absorption of thioglycolic acid (TGA) and up to 2-times enhancement of signals for bovine serum albumin (BSA) protein on plasmonic nanostructure-based films deposited on a silicon (Si) internal reflection element (IRE) compared to bare Si IRE. The dependence of the observed enhancement on the amount of AuNSts present at the surface of the IRE has been demonstrated. Quantitative studies with both, TGA and BSA were performed, observing that the SEIRA signal can be correlated to the concentration of analyte molecules present within the evanescent field. The calibration curves in the presence of the AuNSts showed enhanced sensitivity as compared with the bare Si IRE. We finally compare efficiencies of anisotropic AuNSts and spherical citrate-capped and “bare” laser-synthesized gold nanoparticles as SEIRAS substrates for the detection of TGA and BSA. The signal obtained from AuNSts was at least 2 times higher for TGA molecules in comparison with spherical gold nanoparticles, which was explained by a more efficient generation of hot spots on anisotropic surface due to the presence of sharp edges, tips or vertices, leading to a high electric field strength surrounding the AuNSts.Download high-res image (170KB)Download full-size image

Gas hydrates are ice-like compounds consisting of a rigid water framework hosting small molecules inside crystal cavities. In the present study, a gas hydrate autoclave that enables precise control and observation of temperature and pressure was modified for facilitating in situ mid-infrared spectroscopic studies on the formation of bulk gas hydrates via a polycrystalline silver halide fiber fitted through the vessel serving as active evanescent field sensing element. Methane hydrates were grown inside the autoclave with addition of three different surfactants, i.e., sodium dodecyl sulfate (SDS), dioctyl sodium sulfosuccinate (Aerosol-OT/AOT), and cetylpyridinium chloride (CPC). The accelerating effect of surface-active molecules on the formation of gas hydrates was studied via fiberoptic evanescent field infrared spectroscopy. Thereby, detailed molecular information on the mechanisms of gas hydrate formation and the role of detergents in that process was collected indicating that remaining free guest molecules are in fact trapped within the interstitial water of gas hydrate crystals. Furthermore, the mechanism of gas hydrate formation proposed earlier by our research team for propane could also be confirmed for methane, and for additional detergents thereby leading to a generic mechanism.

The nature of crystallisation processes is of major interest, as they are among the most frequently occurring reactions associated with a variety of relevant processes in chemistry, biochemistry, and geochemistry. In this study, an innovative approach towards fundamentally understanding crystallisation pathways in a seemingly simple system – gypsum – has been developed via infrared spectroscopic techniques. Specifically, infrared attenuated total reflection spectroscopy (IR-ATR) was instrumental in revealing detailed information on inter- and intramolecular interactions during gypsum crystallization via subtle changes in the vibrational spectra of the involved reactants. When applying D2O as an isotope marker, it was shown that isotopically labelled water may serve as a viable spectroscopic probe during mid-infrared (3–15 μm) studies providing unique insight into the crystallization process at molecular-level detail. In addition, it was revealed that H2O and D2O give rise to distinctly different reaction kinetics during the crystallization process.

•Biosynthesis of copper oxide (CuO) nanoparticles their characterization.•Functionalization of screen printed electrodes (SPE) using CuO nanoparticles.•Detection of 4-nitro phenol (4-NP) using functionalized SPE.•Used impedance spectroscopy and square wave voltammetry for detection.•The linear detection range was from 10 nM to 10 mM of 4-NP.The present work reports impedance based electrochemical sensing and remediation of 4-nitro phenol (4-NP) using biosynthesized (CuO) copper oxide nanoparticles. The synthesis of CuO nanoparticles is achieved using fruit extract of plant Fortunella japonica as reducing and stabilizing agent. The CuO nanoparticles were characterized using various analytical techniques like UV–Visible spectroscopy, Atomic force microscopy (AFM), High resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray diffraction (XRD). For electrochemical sensing of 4-NP, the CuO nanoparticles were drop casted on screen printed electrode (SPE) and electrode is referred at SPE/CuONPs sensor. The mechanism of 4-NP redox reactions was examined using cyclic voltammetry (CV). The electrochemical sensing of 4-NP has been done using square wave voltammetry (SWV) and impedance spectroscopy. In SWV, the oxidation peak current increased with increase in the concentration of 4-NP from 10 nM to 10 mM having regression coefficient of 0.996. In impedometric sensing, change in charge transfer resistance (Rct) with change in 4-NP concentration was used as a signal. The Rct decreased with increase in 4-NP concentration which is in accordance with SWV results. The effect of solution pH on impedometric response of SPE/CuONPs sensor was also evaluated. The SPE/CuONPs sensor exhibited good reproducibility and selectivity towards the analyte and is able to perform real sample analysis. The CuO nanoparticles act as a catalyst and showed good degradation percentage of 4-NP pollutant.Download high-res image (113KB)Download full-size image

The synthesis of nanoscale materials has gained considerable attention due to their excellent properties in photocatalysis and also as antimicrobials. More recently, bio-reduction mediated synthesis of such nanostructures has emerged as an environmentally friendly and economical alternative to traditional chemical synthesis. This study describes a strategy for extracellular bio-fabrication of highly stable ZnO nanoparticles from Saccharomyces cerevisiae fungus. The synthesized ZnO nanoparticles were characterized using UV-vis spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The obtained nanoparticles were then assessed for their antibacterial activity against E. Coli MTCC 1302. The photocatalytic performance of these nanoparticles was analyzed by reduction of model dye pollutant, i.e., 4-nitrophenol (4-NP). This study revealed excellent bactericidal and photocatalytic activity of bio-synthesized ZnO nanoparticles. Finally, a potential mechanism for their photocatalytic property is proposed.

A novel approach for molecularly imprinting proteins, i.e. inhibitor-assisted imprinting, onto silica microspheres is discussed, which provides advanced functional materials addressing prevalent challenges in the field of protein purification and isolation from biotechnologically relevant media. Pepstatin-assisted surface-imprinted core–shell microbeads for the acidic protease pepsin were synthesized serving as selective sorbent materials for solid phase extraction (SPE) applications. The inorganic core, i.e. amino-functionalized silica spheres (AFSS), is prepared by the co-condensation of tetraethylorthosilicate (TEOS) and (3-aminopropyl) trimethoxysilane (APTMS) in water-in-oil (W/O) emulsion, which is then reacted with pepstatin, a selective inhibitor of pepsin, onto the surface of the AFSS via an amide bond. 3-Aminophenylboronic acid (APBA) serves as the functional monomer for establishing nanothin imprinted polymer films, i.e. poly(3-aminophenylboronic acid) (pAPBA) at the surface of the pepstatin-immobilized AFSS via oxidation by ammonium persulfate in aqueous solution in the presence (molecularly imprinted polymer, MIP) and absence (non-imprinted polymer; NIP) of pepsin. Thus obtained core–shell microbeads are packaged into SPE cartridges for evaluating the selectivity for pepsin. Each individual synthesis step is thoroughly characterized using x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and BET methods. Finally, the imprinted core–shell microbeads indeed provide specific binding.

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.

Tunable diode laser absorption spectroscopy (TDLAS) is an excellent analytical technique for gas sensing applications. In situ sensing of relevant hydrocarbon gases is of substantial interest for a variety of in-field scenarios including environmental monitoring and process analysis, ideally providing accurate, molecule specific, and rapid information with minimal sampling requirements. Substrate-integrated hollow waveguides (iHWGs) have demonstrated superior properties for gas sensing applications owing to minimal sample volumes required while simultaneously serving as efficient photon conduits. Interband cascade lasers (ICLs) are recently emerging as mid-infrared light sources operating at room temperature, with low power consumption, and providing excellent potential for integration. Thereby, portable and handheld mid-infrared sensing devices are facilitated. Methane (CH4) is among the most frequently occurring, and thus, highly relevant hydrocarbons requiring in situ emission monitoring by taking advantage of its distinct molecular absorption around 3 μm. Here, an efficient combination of iHWGs with ICLs is presented providing a methane sensor calibrated in the range of 100 to 2000 ppmv with a limit of detection at 38 ppmv at the current stage of development. Furthermore, a measurement precision of 0.62 ppbv during only 1 s of averaging time has been demonstrated, thereby rendering this sensor concept useful for in-line and on-site emission monitoring and process control applications.

Synthetic receptors and in particular molecularly imprinted polymers (MIPs) are gaining relevance as selective sorbent materials and biomimetic recognition elements for analyzing polychlorinated aromatic compounds (PACs) in the environment. PACs are still ubiquitous toxic pollutants requiring their continuous environmental assessment for protecting humans and animals from exposure. Since nowadays most PACs occur at ultra-trace concentration levels and in complex matrices, the selectivity of MIPs renders them ideally suited for facilitating either sample pre-treatment and quantitative enrichment, or acting as biomimetic recognition elements as an integral component of corresponding sensing schemes. Due to the diversity of PACs, imprinting polymers for these constituents appears particularly challenging. This review focuses on prevalent strategies towards successfully templating polymer materials towards polychlorinated biphenyls and their hydroxy forms, chlorophenols, dioxins and furans, and organochlorine pesticides, and successful applications of the polymer materials in monitoring of these compounds at trace-levels in real-world environmental matrices. Discussed are also group-selective sorbents for facilitating simultaneous detection and quantification of PACs.

Obtaining in situ information on greenhouse gases arising from deepwater environments is a challenge that has not been satisfactorily resolved to date. An infrared attenuated total reflection (IR-ATR) based on-line sensor system for detecting, monitoring, and differentiating carbon dioxide and methane in dissolved and gaseous states at different pressures (i.e., up to 6 MPa) in saline aquifer and/or synthetic brine environments is presented. It is demonstrated that the detection of dissolved CO2 next to 13CO2 and methane under pressurized conditions is possible under saline downhole conditions, and that gaseous vs. dissolved states of methane and CO2 in aqueous environments may be differentiated using IR-ATR sensing techniques. Finally, it is shown for the first time that there are observable changes associated with distinctive infrared signatures of methane under the conditions of greenhouse gas storage mechanisms. These are of particular importance for advancing carbon capture and storage processes and fundamentally understanding the impact of emissions during the extraction of fossil-based fuels (i.e., shale, petroleum, etc.) from offshore environments.

In this study, ion pairs in aqueous solution were quantitatively and simultaneously determined via infrared attenuated total reflection (IR-ATR) spectroscopy. Seven salts that are occurring in natural seawater, i.e., NaCl, KCl, NaBr, KBr, MgCl2, CaCl2, and Na2SO4 were investigated. Multivariate data analysis was used to discriminate and assign the spectral information arising from each salt in calibration mixtures, each containing a mixture of all constituents in different concentrations. The algorithm was able to discriminate between NaCl/KCl, NaBr/KBr, MgCl2, CaCl2, and Na2SO4 with sodium and potassium chloride, and bromide being treated as sum parameters, respectively. An additional multivariate model was able to distinguish between NaCl, KCl, NaBr, and KBr including their simultaneous quantification. Finally, a sample of real seawater was analyzed, with the established model. MgCl2 could be correctly quantified at 0.5 ± 0.05% (w/v) in this sample, whilst the other ions obviously demand for a more precise and complex calibration model, which is more similar to real seawater.

Research activities on the reduction of carbon dioxide emissions via effective carbon capture and storage (CCS) techniques are steadily increasing with the concept of storing CO2 as hydrates among the most prominently discussed strategies. The present study utilizes mid-infrared (MIR) fiber-optic evanescent field sensing techniques as a promising in situ monitoring tool for investigation of molecular changes occurring during CO2 hydrate formation. The identification and evaluation of characteristic IR absorption features associated with additive molecules (here, THF and SDS) and their changes during hydrate formation were pronounced via studies in D2O next to H2O as the hydrate-forming matrix. By correlating IR-spectroscopic data with continuously recorded pressure and temperature traces, hypotheses on the involvement and promoting effect of such additives during carbon dioxide gas hydrate formation were experimentally consolidated.

The development of a compact iHWG-ICL gas sensor combining innovative substrate-integrated hollow waveguides (iHWG) with mid-infrared emitting type-II interband cascade lasers (ICL) is presented. Hence, tunable laser absorption spectroscopy (TLAS) with iHWGs in direct absorption mode is enabled. Using a room-temperature distributed feedback (DFB) ICL emitting at approximately 3.366 μm, quantitative sensing of methane was demonstrated. Wavelength scanning was obtained via current tuning for monitoring an isolated line in the v3 fundamental band of CH4. The obtained spectra were compared to calculated spectra derived from the HITRAN2012 database. Furthermore, the performance of iHWGs simultaneously serving as miniaturized gas cell and as efficient optical waveguide at various absorption path lengths was tested and optimized. Calibration functions in the concentration range of 50 to 400 ppmv were established enabling limits of detection ranging from 6 to 28 ppmv. Hence, the combination of iHWGs with ICLs facilitates a new generation of compact optical sensor devices for rapid gas diagnostics in low sample volumes.Keywords: absorption spectroscopy; gas sensors; ICL; iHWG; interband cascade laser; methane; mid-infrared; MIR; substrate integrated hollow waveguide

A portable infrared attenuated total reflection (IR-ATR) spectrometer was developed for analyzing CO2 and CH4 in geosequestration scenarios. This infrared-based online sensor system is suitable for monitoring, detecting, and differentiating carbon dioxide and methane at different pressures (i.e., up to 11 MPa) in saline aquifer and/or synthetic brine environments. The design of the sensor system eliminates the present problems in such measurement scenarios of either portability or capability operating at harsh conditions, and especially at elevated pressures for in-field deployment of current available IR systems. It is demonstrated that the detection and quantification of dissolved CO2 and CH4 at pressurized conditions is feasible at relevant saline downhole conditions present within the piping of the present injection wells serving as an online/in-line monitoring tool.Keywords: ATR; attenuated total reflection; carbon capture and storage; environmental monitoring; infrared spectroscopy; mid-infrared

Surface-imprinted polymer particles facilitate the accessibility of synthetic selective binding sites for proteins. Given their volume-to-surface ratio, submicron particles offer a potentially large surface area facilitating fast rebinding kinetics and high binding capacities, as investigated herein by batch rebinding experiments. Polymer particles were prepared with (3-acrylamidopropyl)trimethylammonium chloride as functional monomer, and ethylene glycol dimethacrylate as cross-linker in the presence of pepsin as template molecule via miniemulsion polymerization. The obtained polymer particles had an average particle diameter of 623 nm, and a specific surface area of 50 m2 g−1. The dissociation constant and maximum binding capacity were obtained by fitting the Langmuir equation to the corresponding binding isotherm. The dissociation constant was 7.94 μM, thereby indicating a high affinity; the binding capacity was 0.72 μmol m−2. The binding process was remarkably fast, as equilibrium binding was observed after just 1 min of incubation. The previously determined selectivity of the molecularly imprinted polymer for pepsin was for the first time confirmed during competitive binding studies with pepsin, bovine serum albumin, and β-lactoglobulin. Since pepsin has an exceptionally high content in acidic amino acids enabling strong interactions with positively charged quaternary ammonium groups of the functional monomers, another competitive protein, i.e., α1-acid glycoprotein, was furthermore introduced. This protein has a similarly high content in acidic amino acids, and was used for demonstrating the implications of ionic interactions on the achieved selectivity.

Volatile sulfur compounds (VSCs) are among the most prevalent emitted pollutants in urban and rural atmospheres. Mainly because of the versatility of sulfur regarding its oxidation state (2– to 6+), VSCs are present in a wide variety of redox-environments, concentration levels, and molar ratios. Among the VSCs, hydrogen sulfide and sulfur dioxide are considered most relevant and have simultaneously been detected within naturally and anthropogenically caused emission events (e.g., volcano emissions, food production and industries, coal pyrolysis, and various biological activities). Next to their presence as pollutants, changes within their molar ratio may also indicate natural anomalies. Prior to analysis, H2S- and SO2-containing samples are usually preconcentrated via solid sorbents and are then detected by gas chromatographic techniques. However, such analytical strategies may be of limited selectivity, and the dimensions and operation modalities of the involved instruments prevent routine field usage. In this contribution, we therefore describe an innovative portable mid-infrared chemical sensor for simultaneously determining and quantifying gaseous H2S and SO2 via coupling a substrate-integrated hollow waveguides (iHWG) serving as a highly miniaturized mid-infrared photon conduit and gas cell with a custom-made preconcentration tube and an in-line UV-converter device. Both species were collected onto a solid sorbent within the preconcentrator and then released by thermal desorption into the UV-device. Hydrogen sulfide is detected by UV-assisted quantitative conversion of the rather weak IR-absorber H2S into SO2, which provides a significantly more pronounced and distinctively detectable rovibrational signature. Modulation of the UV-device system (i.e., UV-lamp on/off) enables discriminating between SO2 generated from H2S conversion and abundant SO2 signals. After optimization of the operational parameters, calibrations in the range of 0.75–10 ppmv with a limit of detection (LOD) at 77 ppbv for SO2 and 207 ppbv for H2S were established after 20 min of sampling time at 200 mL min–1. Taking advantage of the device flexibility in terms of sampling time, flow-rate, and iHWG design facilitates tailoring the developed Preconcentrator-UV-device-iHWG device toward a wide variety of application scenarios ranging from environmental/atmospheric monitoring to industrial process monitoring and clinical diagnostics.

In this technical note, we describe an integrated device platform for performing in-flow gaseous conversion reactions based on ultraviolet (UV) irradiation. The system combines, using the same footprint, an integrated UV-conversion device (iCONVERT), a preconcentrator unit (iPRECON), and a new generation of mid-infrared (MIR) gas cell simultaneously serving as a photon conduit, i.e., so-called substrate-integrated hollow waveguide (iHWG) optically coupled to a compact Fourier transform-infrared (FT-IR) spectrometer. The iCONVERT is assembled from two blocks of aluminum (dimensions, 75 mm × 50 mm × 40 mm; L × W × D) containing 4 miniaturized UV-lamps (47mm × 6 mm × 47 mm each). For the present study, the iPRECON-iCONVERT-iHWG sensing platform has specifically been tailored to the determination of H2S in gaseous samples. Thereby, the quantitative UV-assisted conversion of the rather weak IR-absorber H2S into the more pronouncedly responding SO2 is used for hydrogen sulfide detection. A linear calibration model was established in the range of 7.5 to 100 ppmv achieving a limit of detection at 1.5 ppmv using 10 min of sample preconcentration (onto Molecular Sieve 5A) at a flow rate of 200 mL min–1. When compared to a conventional UV-conversion system, the iCONVERT revealed similar performance. Considering the potential for system miniaturization using, e.g., dedicated quantum cascade lasers (QCL) in lieu of the FT-IR spectrometer, the developed sensing platform may be further evolved into a hand-held device.

•PSS-capped ZnO NPs were synthesized via a green electrochemical-thermal method•The influence of electrochemical conditions and temperature was studied•Spectroscopic data show that PSS functionalities are retained in the annealed NPs•Nanostructured ZnO improved the performance of P3HT-based thin film transistorsZnO nanoparticles have been prepared via a green electrochemical synthesis method in the presence of a polymeric anionic stabilizer (poly-sodium-4-styrenesulfonate, PSS), and then applied as inorganic component in poly-3-hexyl-thiophene thin-film transistor active layers. Different parameters (i.e. current density, electrolytic media, PSS concentration, and temperature) influencing nanoparticle synthesis have been studied. The resulting nanomaterials have been investigated by transmission electron microscopy (TEM) and spectroscopic techniques (UV-Vis, infrared, and x-ray photoelectron spectroscopies), assessing the most suitable conditions for the synthesis and thermal annealing of nanostructured ZnO. The proposed ZnO nanoparticles have been successfully coupled with a poly-3-hexyl-thiophene thin-film resulting in thin-film transistors with improved performance.

Carbon nanotubes (CNTs) have demonstrated outstanding chemical and mechanical stability, electrical properties, and strong interactions with aromatic compounds owing to the π-electron system on the graphene sheets. Taking advantage of these unique properties, we have developed a fully validated sample pre-concentration technique for determination of polychlorinated biphenyls (PCBs) in aqueous environments using gas chromatography combined with a micro-cell electron capture detector (GC-μECD). The optimized method using pristine MWCNTs gave recoveries in the range of 46.0–92.5%, 51.4–91.5%, 48.7–77.8% for tap water, river water, and lake water, respectively. Compared to conventional C18 adsorbent and oxidized MWCNTs (oMWCNTs), pristine MWCNTs provided the best recoveries, thereby confirming that MWCNTs are excellent alternatives for C18, with the ability to achieve high performance. The developed protocol achieved method detection limits in the range of 0.002–0.011 μg L−1 and relative standard deviation (RSD) < 15.5%.

In this study, a new generation of integrated preconcentrators particularly suited for exhaled breath gas analysis is described. The developed analyzer system comprises a compact preconcentrator (iPRECON) exemplarily tested for sampling isoprene, which readily couples to substrate-integrated hollow waveguides (iHWGs) of the same footprint serving simultaneously as highly miniaturized gas cell and photon conduit in combination with a compact infrared spectrometer.

The need for continuous monitoring of polychlorinated biphenyls (PCBs) has necessitated the development of analytical techniques that are sensitive and selective with minimal reagent requirement. In light of this, we developed a column for clean-up of soil and sediment extracts, which is less demanding in terms of the amount of solvent and sorbent. The dual-layer column consists of acidified silica gel and molecularly imprinted polymers (MIPs). MIPs were synthesized via aqueous suspension polymerization using PCB 15 as the dummy template, 4-vinylpyridine as the functional monomer and ethylene glycol dimethacrylate as the cross-linker and the obtained particles characterized via SEM, BET, and batch rebinding assays. Pre-concentration of the spiked real-world water sample using MISPE gave recoveries between 85.2 and 104.4% (RSD < 8.69). On the other hand, the specific dual-layer column designed for clean-up of extracts from complex matrices provided recoveries of 91.6–102.5% (RSD < 4%) for spiked soil, which was comparable to clean-up using acidified silica (70.4–90.5%; RSD < 3.72%) and sulfoxide modified silica (89.7–103.0%; RSD < 13.0%). However, the polymers were reusable maintaining recoveries of 79.8–111.8% after 30 cycles of regeneration and re-use, thereby availing a cost-effective clean-up procedure for continuous monitoring of PCBs. Method detection limits were 0.01–0.08 ng g−1 and 0.002–0.01 ng mL−1 for solid matrices and water, respectively.

An infrared attenuated total reflection (IR-ATR) method for detecting, differentiating, and quantifying hydrocarbons dissolved in water relevant for oil spills by evaluating the “fingerprint” of the volatile organic compounds (VOCs) associated with individual oil types in the mid-infrared spectral range (i.e., 800–600 cm–1) is presented. In this spectral regime, these hydrocarbons provide distinctive absorption features, which may be used to identify specific hydrocarbon patterns that are characteristic for different crude and refined oils. For analyzing the “VOC fingerprint” resulting from various oil samples, aqueous solutions containing the dissolved hydrocarbons from different crude oils (i.e., types “Barrow”, “Goodwyn”, and “Saladin”) and refined oils (i.e., “Petrol” and “Diesel”) were analyzed using a ZnSe ATR waveguide as the optical sensing element. To minimize interferences from the surrounding water matrix and for amplifying the VOC signatures by enrichment, a thin layer of poly(ethylene-co-propylene) was coated onto the ATR waveguide surface, thereby enabling the establishment of suitable calibration functions for the quantification of characteristic concentration patterns of the detected VOCs. Multivariate data analysis was then used for a prelininary classification of various oil-types via their VOC patterns.

The first combination of mid-infrared (MIR) tunable quantum cascade lasers (tQCLs) with thin-film diamond strip waveguides (DSWGs) suitable for advanced chemical sensing/biosensing is demonstrated. The sensing system is composed of thin diamond films grown on surface-passivated Si wafers via chemical vapor deposition (CVD) and microstructured using inductively coupled plasma (ICP) etching, serving as photonic waveguides for radiation emitted by a broadly tunable quantum cascade laser (tQCL) in the spectral regime of 5.78–6.35 μm (1570–1730 cm–1). The characterization of the free-standing diamond waveguides reveals excellent transmission properties across a broad MIR band. As a proof of concept, the detection of acetone in D2O via evanescent field absorption is demonstrated achieving a limit of detection (LOD) as low as 200 pL, which indicates a significant sensitivity improvement compared to conventional MIR slab/strip waveguides reported to date. Providing characteristic absorption features within the tuning range of the tQCL, studies using anisaldehyde as an analyte further corroborate the potential of tQCL-DSWG-based chemical sensors/biosensors.

Hydrogen sulfide is a highly corrosive, harmful, and toxic gas produced under anaerobic conditions within industrial processes or in natural environments, and plays an important role in the sulfur cycle. According to the U.S. Occupational Safety and Health Administration (OSHA), the permissible exposure limit (during 8 hours) is 10 ppm. Concentrations of 20 ppm are the threshold for critical health issues. In workplace environments with human subjects frequently exposed to H2S, e.g., during petroleum extraction and refining, real-time monitoring of exposure levels is mandatory. Sensors based on electrochemical measurement principles, semiconducting metal-oxides, taking advantage of their optical properties, have been described for H2S monitoring. However, extended response times, limited selectivity, and bulkiness of the instrumentation are common disadvantages of the sensing techniques reported to date. Here, we describe for the first time usage of a new generation of compact gas cells, i.e., so-called substrate-integrated hollow waveguides (iHWGs), combined with a compact Fourier transform infrared (FTIR) spectrometer for advanced gas sensing of H2S. The principle of detection is based on the immediate UV-assisted conversion of the rather weak IR-absorber H2S into much more pronounced and distinctively responding SO2. A calibration was established in the range of 10–100 ppm with a limit of detection (LOD) at 3 ppm, which is suitable for occupational health monitoring purposes. The developed sensing scheme provides an analytical response time of less than 60 seconds. Considering the substantial potential for miniaturization using e.g., a dedicated quantum cascade laser (QCL) in lieu of the FTIR spectrometer, the developed sensing approach may be evolved into a hand-held instrument, which may be tailored to a variety of applications ranging from environmental monitoring to workplace safety surveillance, process analysis and clinical diagnostics, e.g., breath analysis.

•Direct quantification of perfluorinated hydrocarbons with a mid-infrared sensor.•A mid-infrared sensor overcomes issues with sampling and sample preparation.•A mid-infrared sensor for monitoring perfluorinated hydrocarbons in aquifers.Perfluorocarbon (PFC) compounds have been used as chemical tracer molecules to understand the movement of supercritical carbon dioxide for geosequestration monitoring and verification purposes. A commonly used method for detecting PFCs involves the collection of a sample from either soil-gas or the atmosphere via carbon-based sorbents which are then analyzed in a laboratory. However, PFC analysis in aquatic environments is neglected and this is an issue that needs to be considered since the PFC is likely to undergo permeation through the overlying water formations. This paper presents for the first time an innovative analytical method for the trace level in situ detection of PFCs in water. It reports on the development of a sensor based on mid-infrared attenuated total reflection (MIR-ATR) spectroscopy for determining the concentration of perfluoromethylcyclohexane (PMCH) and perfluoro-1,3-dimethylcyclohexane (PDCH) in aquatic systems. The sensor comprises a zinc selenide waveguide with the surface modified by a thin polymer film. The sensitivity of this device was investigated as a function of polymer type, coating thickness, and solution flow rates. The limit of detection (LOD) was determined to be 23 ppb and 79 ppb for PMCH and PDCH, respectively when using a 5 μm thick polyisobutylene (PIB) coated waveguide. This study has shown that the MIR-ATR sensor can be used to directly quantify PFC-based chemical tracer compounds in water over the 20–400 ppb concentration range.

Surface imprinted polymers allow accessibility of the selective binding sites to large molecules such as proteins. In this work, small polymer particles offering a large surface area were prepared via miniemulsion polymerization in the presence of pepsin serving as a template molecule. The influence of four different functional monomers and of the amount of the template on the imprinting effect of pepsin was investigated. After the miniemulsion polymerization and a washing step, stable polymer suspensions with an average particle diameter of 400–600 nm and a specific surface area of 30–65 m2 g−1 were obtained. The results of detailed rebinding experiments revealed that the highest imprinting effect was achieved with (3-acrylamidopropyl)trimethylammonium chloride as a functional monomer and a high amount of the template. These polymer particles also showed selectivity for pepsin against various proteins. This approach provides a fundamental step towards the development of synthetic protein receptors and protein scavenger materials useful in biomimetic assays and for clean-up in biotechnology.

Lung epithelia regulate the water flux between gas filled airways and the interstitial compartment in order to maintain organ function. Current methodology to assess transepithelial water transport is limited. We present a D2O dilution method to quantify submicroliter volumes of aqueous solutions on epithelial cell layers. Evaluating D2O/H2O mixtures using mid-infrared (2–25 μm) attenuated total reflection (ATR) spectroscopy, with a resolution of 0.06% vol/vol change, corresponding to 24 nL, was achieved. Using this method, we demonstrate that water transport across NCI-H441 lung epithelial cell layers and apical surface liquid (ASL) volumes are coupled to dexamethasone dependent amiloride-sensitive ion transport. However, contrary to current dogma, electrogenic transport is not rate-limiting for water transport. This clearly indicates the need to directly assess net water rather than ion transport across epithelial cell layers. The presented D2O dilution method enables such direct and quick quantification of transepithelial water transport with high resolution.

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 12CO2 and 13CO2 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 12CO2/13CO2 spectral band with a miniaturized hollow waveguide gas cell for quantitatively determining the 12CO2/13CO2 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.

We report the design, fabrication, and first functional verification of mid-infrared (MIR; 3–12 μm) Mach–Zehnder interferometers (MZIs). The developed MIR-MZIs are entirely chip-integrated solid-state devices based on GaAs/AlGaAs technology waveguide fabricated via conventional optical lithography and reactive ion etching (RIE). Thus, fabricated MIR-MZIs were combined with a broadly tunable quantum cascade laser (tQCL) providing a wavelength coverage of 5.78–6.35 μm. MIR-MZIs have been designed with a waveguide width of 5 μm to ensure single mode behavior, avoiding optically undefined interference patterns. Several structures with different opening angles of the Y-junction were fabricated and tested for maximizing IR radiation throughput. This study demonstrates the feasibility of the very first chip-integrated mid-infrared Mach–Zehnder structures via interference patterns produced by minute amounts of water deposited at different positions of the MIR-MZI structure.

We report the first planar waveguides made from mercury–cadmium–telluride (MCT)—a material to date exclusively used for mid-infrared (MIR) detector elements—serving as on-chip MIR evanescent field transducers in combination with tunable quantum cascade lasers (tQCLs) emitting in the spectral regime of 5.78–6.35 μm. This novel MIR sensing approach utilizes structured MCT chips fabricated via molecular beam epitaxy (MBE) as waveguide enabling sensing via evanescent field absorption spectroscopy, as demonstrated by the detection of 1 nL of acetone. Complementary finite difference time domain (FDTD) simulations fit well with the experimentally obtained data and predict an improvement of the limit of detection by at least 2 orders of magnitude upon implementation of thinner MCT waveguides. With the first demonstration of chemical sensing using on-chip MCT waveguides, monolithically fabricated IR sensing systems directly interfacing the waveguide with the MCT detector element may be envisaged.

A new generation of hollow waveguide (HWG) gas cells of unprecedented compact dimensions facilitating low sample volumes suitable for broad- and narrow-band mid-infrared (MIR; 2.5–20 μm) sensing applications is reported: the substrate-integrated hollow waveguide (iHWG). iHWGs are layered structures providing light guiding channels integrated into a solid-state substrate material, which are competitive if not superior in performance to conventional leaky-mode fiber optic silica HWGs having similar optical pathlengths. In particular, the provided flexibility in device and optical design and the wide variety of manufacturing strategies, substrate materials, access to the optical channel, and optical coating options highlight the advantages of iHWGs in terms of robustness, compactness, and cost-effectiveness. Finally, the unmatched modularity of this novel waveguide approach facilitates tailoring iHWGs to almost any kind of gas sensor technology providing adaptability to the specific demands of a wide range of sensing scenarios. Device fabrication is demonstrated for the example of a yin-yang-shaped gold-coated iHWG fabricated within an aluminum substrate with a footprint of only 75 mm × 50 mm × 12 mm (L × W × H), yet providing a nominal optical absorption path length of more than 22 cm. The analytical utility of this device for advanced MIR gas sensing applications is demonstrated for the gaseous constituents butane, carbon dioxide, cyclopropane, isobutylene, and methane.

The structural integrity and protection of bacterial biofilms are intrinsically associated with a matrix of extracellular polymeric substances (EPS) produced by the bacteria cells. However, the role of these substances during biofilm adhesion to a surface remains largely unclear. In this study, the influence of EPS on Xylella fastidiosa biofilm formation was investigated. This bacterium is associated with economically important plant diseases; it presents a slow growth rate and thus allows us to pinpoint more precisely the early stages of cell-surface adhesion. Scanning electron microscopy and atomic force microscopy show evidence of EPS production in such early stages and around individual bacteria cells attached to the substrate surface even a few hours after inoculation. In addition, EPS formation was investigated via attenuated total reflectance (ATR) Fourier transform infrared spectroscopy (FTIR). To this end, X. fastidiosa cells were inoculated within an ATR liquid cell assembly. IR–ATR spectra clearly reveal EPS formation already during the early stages of X. fastidiosa biofilm formation, thereby providing supporting evidence for the hypothesis of the relevance of the EPS contribution to the adhesion process.Graphical abstractHighlights► SEM and AFM images suggest EPS production during all stages of biofilm formation. ► IR–ATR spectra reveal EPS production since early stages of X. fastidiosa biofilm. ► Our results suggest EPS is extensively involved in irreversible adhesion processes.

The determination of trace amounts of oil in water facilitates the forensic analysis on the presence and origin of oil in the aqueous environment. To this end, the present study focuses on direct sensing schemes for quantifying trace amounts of oil in water using mid-infrared (MIR) evanescent field absorption spectroscopy via fiberoptic chemical sensors. MIR transparent silver halide fibers were utilized as optical transducer for interrogating oil-in-water emulsions via the evanescent field emanating from the waveguide surface, and penetrating the surrounding aqueous environment by a couple of micrometers. Unmodified fibers and fibers surface-modified with grafted epoxidized polybutadiene layers enabled the direct detection of crude oil in a deionized water matrix at the ppm level to ppb concentration level, respectively. Thus, direct chemical sensing of crude oil IR signatures without any sample preparation as low as 46 ppb was achieved with a response time of a few seconds.

In molecular imprinting the porogen plays a decisive role, as it not only affects the physical properties of the resulting polymer including its porosity, the specific surface area, and the swelling behavior, but also governs the stability of the prepolymerization complex, which in turn decisively determines the recognition properties of the resulting molecularly imprinted polymer (MIP).In this study, the influence of the porogen on the selectivity of MIPs was investigated. Therefore, bulk MIPs against 4-nitrophenol using 4-vinylpyridine (4-VP) as functional monomer and ethylene glycol dimethacrylate (EDMA) as crosslinker were prepared in acetonitrile and chloroform. The recognition properties of both MIPs were evaluated during chromatographic studies using the respective porogenic solvents as mobile phase for both MIPs. Along with the characterization of the morphology of the obtained polymers via SEM and BET analysis, the beneficial nature of chloroform as porogen for imprinting 4-NP was experimentally demonstrated and verified by findings obtained from complementary molecular dynamics simulations. Moreover, the application of chloroform as mobile phase for the MIP prepared in acetonitrile and vice versa clearly demonstrated the dependence of the resulting recognition properties on the selection of the mobile phase.Graphical abstractHighlights► Influence of the porogenic solvent on the selectivity of MIPs was investigated. ► Recognition properties in different porogens were evaluated via chromatography. ► Role of the porogen was studied via complementary molecular dynamics simulations.

Water is a common contaminant in a variety of industrial oils and petroleum products. Thus, the detection of water in these products is of substantial relevance. Hence, this study focuses on quantifying trace amounts of water in hydrocarbons using hexane as a model system for industrial oils and petroleum matrices via mid-infrared (MIR) evanescent field absorption spectroscopy. A silver halide fiberoptic waveguide was used to interrogate in situwater-in-hexane emulsions. Either unmodified fibers or waveguides surface-modified with polyacrylic acid layers were used. The limits of detection (LOD) and limits of quantification (LOQ) of water in hexane utilizing tin-crosslinked polyacrylic acid modified fibers were 76 and 170 ppm, respectively. Consequently, the IR absorption signature of water in hexane is detectable at concentrations as low as 10 ppm. The proposed fiberoptic sensing strategy requires a single measurement only, requires no sample preparation, and thus has potential for the direct in situ detection and monitoring of water in industrial oils and petroleum products.

We demonstrate ultra-sensitive chemical sensing in the mid-infrared spectral regime with a combination of quantum cascade lasers (QCLs) with GaAs/Al0.2Ga0.8As strip waveguides fabricated via metal–organic vapor-phase epitaxy (MOVPE) and reactive ion etching (RIE) using evanescent field absorption spectroscopy. These strip waveguides have been designed with a width of 200 μm, thereby facilitating 2-D confinement and mode-matched propagation of mid-infrared radiation emitted from a distributed feedback (DFB) QCL at a wavelength of 10.3 μm. Acetic anhydride was detected with a limit of detection (LOD) of 18 pL (19.4 ng) deposited at the waveguide surface by overlapping of the vibrational absorption of the methyl group with the emission frequency of the QCL. The obtained results indicate a remarkable enhancement in sensitivity by three orders of magnitude compared to previously reported multimode planar silver halide waveguides. Further reduction of the waveguide strip width to 50 μm resulted in an additional sensitivity enhancement yielding a calculated LOD of 0.05 pL for the exemplary analyte acetic anhydride, which is among the most sensitive evanescent field absorption measurements with a miniaturized mid-infrared sensor system reported to date.

The cathodic electropolymerization conditions for poly(4-vinylpyridine) and the uptake characteristics of anions were evaluated with respect to their application to electrochemical sensing. The membranes were deposited from acidified acetonitrile solutions to minimize hydrogen gas evolution, which is prevalent in aqueous media at the applied potential range. Mid-infrared spectroscopic studies resulted in quantitative data relating the amount of monomer protonated with respect to the added acid, while 1H nuclear magnetic resonance spectroscopy provided insight into the resonance form preferentially adopted by the protonated monomer. The presence of defects in poly(4-VP) films was indirectly measured by monitoring the obstructed diffusion of cationic redox species through the film, and by correlating these electrochemical studies with mid-infrared spectroscopic analysis it became possible to determine the protonated-to-unprotonated monomer ratio yielding uniformly coated electrodes. Finally, the diffusion of Fe(CN)64− through poly(4-VP)-coated electrodes was evaluated as a function of pH, resulting in the conclusion that, unlike similarly deposited poly(2-VP) membranes, poly(4-VP) does not possess the loading capacity required for pre-concentration of anions.

With inductively coupled plasma optical emission spectroscopy (ICP-OES), this article introduces an analysis method enabling the direct quantitative determination of residual template molecules in molecularly imprinted polymer (MIP) matrices. ICP-OES was applied for the determination of residual iodine in MIPs prepared against the iodinated X-ray contrast agent iohexol. Prior to analysis, a microwave-assisted acidic oxidative digestion method was developed simultaneously enabling the digestion of the polymer matrix and the exhaustive oxidation of organically bound iodine. Excellent recovery rates and a high accuracy confirm the feasibility and utility of a microwave-assisted digestion with subsequent ICP-OES analysis for the determination of residual iodine in MIPs, and indicate the potential of this combination as a widely applicable monitoring tool for the efficiency of template extraction from MIP matrices.

For the efficient usage of molecularly imprinted polymers (MIPs) with minimal template leaching, a comprehensive clean-up of the synthesized polymer particles is of critical importance. Predominantly the template molecules, and also the unreacted functional monomer and cross-linker should be exhaustively removed for ensuring reliable results, in particular if MIPs are used within quantitative analytical applications such as e.g., in binding assays or in solid phase extraction. However, an exhaustive clean-up is considered a tedious procedure, which is time-consuming and requires substantial amounts of extraction solvent. In order to significantly improve the efficiency of this crucial step during MIP synthesis, a novel extractor device was developed, which facilitates the rapid and efficient clean-up of particulate polymer matrices, and which is particularly tailored toward the extraction of template molecules from imprinted polymer particles. Compared to commonly applied cleaning procedures such as Soxhlet extraction or HPLC extraction methods, this device offers significant advantages including e.g., the usage of solvent mixtures, temperature-controlled extraction conditions, improved kinetics, and continuous control of the extraction process. First results demonstrating the functionality of the device are discussed for the extraction of molecularly imprinted polymers against the radio contrast agent iohexol.

Studies on particulate quartz and silica films were performed using Fourier transform infrared spectroscopy (FT-IR) via attenuated total reflection (ATR). Based on the fact that measurements in the visible and near-infrared (vis/NIR) spectral range are already applied to spectrally distinguish disturbed from undisturbed soils, measurements in the mid-infrared (MIR) regime were performed to further investigate the utility of longer wavelengths toward this analytical problem. Natural particulate quartz samples were selected to provide a simplified surrogate for the dominating component of most soil matrices; water was added to simulate weathering processes of this matrix. Adding water to the pristine quartz particulate film resulted in a strong spectral shift of the asymmetric Si–O–Si stretch vibration at 1090 cm–1, thus substantiating the hypothesis of a size-related shift of the absorption wavelength due to changes in the particle size distribution within the evanescent field that is extending a few micrometers into the particle layer near the ATR surface. Monodisperse soda lime glass spheres and silica microsphere samples were then investigated at simulated weathering conditions to corroborate this assumption. The obtained results indeed demonstrate that spectra recorded at monodisperse particles do not reveal any spectral shifts during simulated weathering, which again confirms a particle size-related effect. In addition, studies using unpolarized and polarized IR radiation revealed a distinct correlation between the shifts of the major absorption features, i.e., the TO modes, and the particle size.

Simultaneous and molecularly selective parts-per-billion detection of benzene, toluene, and xylenes (BTX) using a thermal desorption (TD)-FTIR hollow waveguide (HWG) trace gas sensor is demonstrated here for the first time combining laboratory calibration with real-world sample analysis in field. A calibration range of 100–1000 ppb analyte/N2 was developed and applied for predicting the concentration of blinded environmental air samples within the same concentration range, and demonstrate close agreement with the validation method used here, GC-FID. The analyte concentration prediction capability of the TD-FTIR-HWG trace gas sensor also compares well with the industrial standard and other experimental techniques including GC-PID, ultrafast GC-FID, and GC-DMS, which were simultaneously operated in the field. With the advent of a quantum cascade laser with emission frequencies specifically tailored to efficiently overlap benzene absorption as the most relevant analyte, the overall sensor footprint could be considerably reduced to ultimately yield hand-held trace gas sensors facilitating direct and real-time detection of BTX in air down to low ppb levels.

Biofilms are complex microbial communities with important biological functions including enhanced resistance against external factors like antimicrobial agents. The formation of a biofilm is known to be strongly dependent on substrate properties including hydrophobicity/hydrophilicity, structure, and roughness. The adsorption of (macro)molecules on the substrate, also known as conditioning film, changes the physicochemical properties of the surface and affects the bacterial adhesion. In this study, we investigate the physicochemical changes caused by Periwinkle wilt (PW) culture medium conditioning film formation on different surfaces (glass and silicon) and their effect on X. fastidiosa biofilm formation. Contact angle measurements have shown that the film formation decreases the surface hydrophilicity degree of both glass and silicon after few hours. Atomic force microscopy (AFM) images show the glass surface roughness is drastically reduced with conditioning film formation. First-layer X. fastidiosa biofilm on glass was observed in the AFM liquid cell after a period of time similar to that determined for the hydrophilicity changes. In addition, attenuation total reflection–Fourier transform infrared (ATR-FTIR) spectroscopy supports the AFM observation, since the PW absorption spectra increases with time showing a stronger contribution from the phosphate groups. Although hydrophobic and rough surfaces are commonly considered to increase bacteria cell attachment, our results suggest that these properties are not as important as the surface functional groups resulting from PW conditioning film formation for X. fastidiosa adhesion and biofilm development.Graphical abstractConditioning film formed by culture medium affects the roughness, hydrophobicity, and chemical composition of the surface. Our results indicate that chemical surface changes are involved in facilitating biofilm growth.Figure optionsDownload full-size imageDownload high-quality image (68 K)Download as PowerPoint slideHighlights► Periwinkle wilt (PW) culture medium forms conditioning film on different surfaces. ► This film changes the surface hydrophobicity, roughness, and chemical composition. ► Chemical surface changes are involved in facilitating biofilm growth. ► Results are correlated well with current models for Xylella fastidiosa cell adhesion.

This communication presents a novel label-free biosensing method to monitor DNA hybridization via infrared attenuated total reflection (IR-ATR) spectroscopy using surface-modified ZnSe waveguides. Well-defined carboxyl-terminated monolayers were formed at H-terminated ZnSe by direct photochemical activation. Chemical activation of the acidic function was obtained by using succinimide/carbodiimide linkers. The sequential surface modification reactions were characterized by XPS and IR-ATR spectroscopy. Finally, a single stranded DNA probe with a C6–NH2 5′ modifier was coupled to the ester-terminated surface viapeptide bonding, and the hybridization of the immobilized DNA sequence with its complementary strand was directly evaluated by IR-ATR spectroscopy in the mid-infrared (MIR) spectral regime (3–20 μm) without requiring an additional label. A shift of the vibrational modes corresponding to the phosphodiester and deoxyribose structures of the DNA backbone was observed. Hence, this approach substantiates a novel strategy for label-free DNA detection utilizing mid-infrared spectroscopy as the optical sensing platform.

This contribution describes the development of nitrogen-doped diamond-like carbon (N-DLC) thin films for multi-reflection mid-infrared (MIR) attenuated total reflectance (IR-ATR) spectroelectrochemistry. N-DLC coatings were deposited using pulsed laser deposition (PLD) involving the ablation of a high purity graphite target. The DLC matrix was further modified by ablating the target in the presence of nitrogen gas. This technique offers the advantage of depositing thin films at room temperature, thereby enabling coating of temperature-sensitive substrates including e.g., MIR waveguides. The resulting films were analyzed with X-ray photoelectron spectroscopy (XPS), and determined to be composed of carbon, nitrogen, and adventitious oxygen. Raman spectroscopic studies indicate that the addition of nitrogen induces further clustering and ordering of the sp2-hybridized carbon phase. The electrochemical activity of PLD fabricated N-DLC films was verified using the Ru(NH3)3+/2+redox couple, and was determined to be comparable with that of other carbon-based electrodes. In situ spectroelectrochemical studies involving N-DLC coated zinc selenide (ZnSe) MIR waveguides provided evidence concerning the oxidation of N-DLC at anodic potentials in 1 M HClO4 solutions. Finally, the electropolymerization of polyaniline (PAni) was performed at N-DLC-modified waveguide surfaces, which enabled spectroscopic monitoring of the electropolymerization, as well as in situ studying the structural conversion of PAni at different potentials.

Infrared attenuated total reflection (IR-ATR) spectroscopy was applied to analyze carbonates in sediment samples collected at a cold seep site in Mississippi Canyon 118, Gulf of Mexico. Previously, these samples were grouped into low, moderate, and high microbial activity based on sulfate and methane down-core profiles. We have hypothesized that within these groups, IR-ATR spectroscopy could differentiate between cold seep derived microbially mediated authigenic carbonates found in high and moderate microbially active sediments, and biogenically produced carbonates representative for low microbially active sediments. Within the respective IR spectroscopic absorption profiles, the ν3antisymmetric carbonate stretching vibration was identified as a suitable indicator within these diverse geochemical groupings. Low microbial activity cores revealed absorption profiles that are significantly different from those of high and moderate microbial activity cores. To verify the IR-ATR results, the obtained spectral profiles were compared to stable isotopic values of in situ bulk carbonate signals. It is shown that for carbonates depleted in δ13C (negative values), the IR ν3 profiles are uniquely different. To semi-quantify this method, the obtained IR profiles were utilized for deriving an IR indicator (F) for establishing an analytical model suitable for the identification of cold seep derived authigenic carbonate. The sediment samples characterized by cold seep derived authigenic carbonates have an average indicator F value of 104.3 ± 15.8, whereas biogenic carbonates show F values of 53.5 ± 11.4. The obtained results demonstrate that IR-ATR spectroscopy may be applied as a shipboard and potentially in situ research tool for rapid and cost-effective characterization of carbonate formations in cold seep ecosystems.Research Highlights► IR-ATR spectroscopy used for studying carbonate minerals within marine sediments. ► Semi-quantitative method for determining calcite–dolomite composition in sediments established. ► IR signature of the ν3antisymmetric C―O stretching vibration enables detection of authigenic carbonates. ► Potential of IR-ATR spectroscopy for direct on-ship and in future in situ analysis demonstrated.

Single-bounce attenuated total reflection infrared spectroscopy in the 3−20 μm range (mid-infrared, MIR) has been combined with scanning electrochemical microscopy (SECM) for in situ spectroscopic detection of electrochemically induced localized surface modifications using an ultramicroelectrode (UME). In this study, a novel current-independent approach for positioning the UME in aqueous electrolyte solution is presented using either changes of infrared (IR) absorption intensity associated with borosilicate glass (BSG), which is used as shielding material of the UME wire, or by monitoring IR changes of the water spectrum within the penetration depth of the evanescent field due to displacement of water molecules in the volume between the sample surface and the UME within the evanescent field. The experimental results show that the UME penetrates into the exponentially decaying evanescent field in close vicinity (a few micrometer) to the attenuated total reflection (ATR) crystal surface. Hence, the resulting intensity changes of the IR absorption spectra for borosilicate glass (increase) and for water (decrease) can be used to determine the position of the UME relative to the ATR crystal surface independent of the current measured at the UME.

In the present study, the quantitative determination of the diamondoid compound adamantane in organic solvents via infrared attenuated total reflection (IR-ATR) spectroscopy at unmodified waveguide surfaces was established. Limits of detection (LOD) and quantification (LOQ) of adamantane in dichloromethane, hexane and carbon tetrachloride were determined. Quantitative IR-ATR measurements additionally facilitated the determination of adamantane solubility limit in dichloromethane, hexane and carbon tetrachloride. The developed analytical strategy further enabled the successful detection and quantification of adamantane in crude oil matrices. Consequently, IR-ATR spectroscopy provides a promising strategy for on ship and in situ diamondoid analysis in harsh real world environments.

In the study presented here, quantitative detection of ethyl chloride, dichloromethane, and trichloromethane individually and in mixture has been demonstrated using an external cavity broadly tunable quantum cascade laser (EC-QCL) based hollow waveguide gas sensor. The EC-QCL has been characterized by coupling into a FT-IR spectrometer documenting sufficient optical power output across a frequency tuning range from 1297 cm−1 to 1219 cm−1. Concentrations as low as 4 ppb for ethyl chloride, 7 ppm for dichloromethane, and 11 ppb for trichloromethane were detected during exponential dilution experiments with the EC-QCL precisely tuned to selective absorption frequencies of the Q-branch for each constituent at 1287.25 cm−1, 1262 cm−1, and 1220 cm−1, respectively.

•The inter-occasional distribution of coefficients for a nonlinear calibration curve is assessed.•Coefficients of an actual calibration curve are a sample of the inter-occasional distribution.•This sample and few actual measurements are sufficient to assess an actual calibration curve.•A new calibration transfer method is proposed using minimal calibration effort.•The model is confirmed by random subset cross validation for the calibration of an oxygen sensor.The calibration of analytical systems is time-consuming and the effort for daily calibration routines should therefore be minimized, while maintaining the analytical accuracy and precision. The ‘calibration transfer’ approach proposes to combine calibration data already recorded with actual calibrations measurements. However, this strategy was developed for the multivariate, linear analysis of spectroscopic data, and thus, cannot be applied to sensors with a single response channel and/or a non-linear relationship between signal and desired analytical concentration. To fill this gap for a non-linear calibration equation, we assume that the coefficients for the equation, collected over several calibration runs, are normally distributed. Considering that coefficients of an actual calibration are a sample of this distribution, only a few standards are needed for a complete calibration data set. The resulting calibration transfer approach is demonstrated for a fluorescence oxygen sensor and implemented as a hierarchical Bayesian model, combined with a Lagrange Multipliers technique and Monte-Carlo Markov-Chain sampling. The latter provides realistic estimates for coefficients and prediction together with accurate error bounds by simulating known measurement errors and system fluctuations. Performance criteria for validation and optimal selection of a reduced set of calibration samples were developed and lead to a setup which maintains the analytical performance of a full calibration. Strategies for a rapid determination of problems occurring in a daily calibration routine, are proposed, thereby opening the possibility of correcting the problem just in time.Figure optionsDownload full-size imageDownload high-quality image (305 K)Download as PowerPoint slide

The main objective of this study is to expand the understanding on the role of surfactants during gas hydrate formation at surfaces. It is shown that in situ studies using mid-infrared (MIR) evanescent field absorption spectroscopy utilizing silver halide fiberoptic waveguides routed through a pressurized cell enables detailed spectroscopic observations of detergent-related surface processes during sodium dodecyl sulfate (SDS) mediated gas hydrate formation. Thereby, processes involving the key molecular players– water, SDS, and propane gas – were spectroscopically monitored in close vicinity of the fiber surface, thus providing evidence for the role of SDS as a promoter of gas hydrate growth. Based on insight on the individual contributions of the involved molecules, a mechanism for the SDS-induced decrease of hydrate nucleation time is proposed.Graphical abstractDownload high-res image (105KB)Download full-size imageHighlights► Molecularly detailed in-situ IR spectroscopic study of gas hydrate formation. ► Unraveling the role of SDS during gas hydrate formation. ► Fundamental understanding on the molecular mechanism of gas hydrate formations in the presence of a detergent.

The need for continuous monitoring of polychlorinated biphenyls (PCBs) has necessitated the development of analytical techniques that are sensitive and selective with minimal reagent requirement. In light of this, we developed a column for clean-up of soil and sediment extracts, which is less demanding in terms of the amount of solvent and sorbent. The dual-layer column consists of acidified silica gel and molecularly imprinted polymers (MIPs). MIPs were synthesized via aqueous suspension polymerization using PCB 15 as the dummy template, 4-vinylpyridine as the functional monomer and ethylene glycol dimethacrylate as the cross-linker and the obtained particles characterized via SEM, BET, and batch rebinding assays. Pre-concentration of the spiked real-world water sample using MISPE gave recoveries between 85.2 and 104.4% (RSD < 8.69). On the other hand, the specific dual-layer column designed for clean-up of extracts from complex matrices provided recoveries of 91.6–102.5% (RSD < 4%) for spiked soil, which was comparable to clean-up using acidified silica (70.4–90.5%; RSD < 3.72%) and sulfoxide modified silica (89.7–103.0%; RSD < 13.0%). However, the polymers were reusable maintaining recoveries of 79.8–111.8% after 30 cycles of regeneration and re-use, thereby availing a cost-effective clean-up procedure for continuous monitoring of PCBs. Method detection limits were 0.01–0.08 ng g−1 and 0.002–0.01 ng mL−1 for solid matrices and water, respectively.

A novel approach for molecularly imprinting proteins, i.e. inhibitor-assisted imprinting, onto silica microspheres is discussed, which provides advanced functional materials addressing prevalent challenges in the field of protein purification and isolation from biotechnologically relevant media. Pepstatin-assisted surface-imprinted core–shell microbeads for the acidic protease pepsin were synthesized serving as selective sorbent materials for solid phase extraction (SPE) applications. The inorganic core, i.e. amino-functionalized silica spheres (AFSS), is prepared by the co-condensation of tetraethylorthosilicate (TEOS) and (3-aminopropyl) trimethoxysilane (APTMS) in water-in-oil (W/O) emulsion, which is then reacted with pepstatin, a selective inhibitor of pepsin, onto the surface of the AFSS via an amide bond. 3-Aminophenylboronic acid (APBA) serves as the functional monomer for establishing nanothin imprinted polymer films, i.e. poly(3-aminophenylboronic acid) (pAPBA) at the surface of the pepstatin-immobilized AFSS via oxidation by ammonium persulfate in aqueous solution in the presence (molecularly imprinted polymer, MIP) and absence (non-imprinted polymer; NIP) of pepsin. Thus obtained core–shell microbeads are packaged into SPE cartridges for evaluating the selectivity for pepsin. Each individual synthesis step is thoroughly characterized using x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and BET methods. Finally, the imprinted core–shell microbeads indeed provide specific binding.

For the efficient usage of molecularly imprinted polymers (MIPs) with minimal template leaching, a comprehensive clean-up of the synthesized polymer particles is of critical importance. Predominantly the template molecules, and also the unreacted functional monomer and cross-linker should be exhaustively removed for ensuring reliable results, in particular if MIPs are used within quantitative analytical applications such as e.g., in binding assays or in solid phase extraction. However, an exhaustive clean-up is considered a tedious procedure, which is time-consuming and requires substantial amounts of extraction solvent. In order to significantly improve the efficiency of this crucial step during MIP synthesis, a novel extractor device was developed, which facilitates the rapid and efficient clean-up of particulate polymer matrices, and which is particularly tailored toward the extraction of template molecules from imprinted polymer particles. Compared to commonly applied cleaning procedures such as Soxhlet extraction or HPLC extraction methods, this device offers significant advantages including e.g., the usage of solvent mixtures, temperature-controlled extraction conditions, improved kinetics, and continuous control of the extraction process. First results demonstrating the functionality of the device are discussed for the extraction of molecularly imprinted polymers against the radio contrast agent iohexol.

Surface imprinted polymers allow accessibility of the selective binding sites to large molecules such as proteins. In this work, small polymer particles offering a large surface area were prepared via miniemulsion polymerization in the presence of pepsin serving as a template molecule. The influence of four different functional monomers and of the amount of the template on the imprinting effect of pepsin was investigated. After the miniemulsion polymerization and a washing step, stable polymer suspensions with an average particle diameter of 400–600 nm and a specific surface area of 30–65 m2 g−1 were obtained. The results of detailed rebinding experiments revealed that the highest imprinting effect was achieved with (3-acrylamidopropyl)trimethylammonium chloride as a functional monomer and a high amount of the template. These polymer particles also showed selectivity for pepsin against various proteins. This approach provides a fundamental step towards the development of synthetic protein receptors and protein scavenger materials useful in biomimetic assays and for clean-up in biotechnology.

With inductively coupled plasma optical emission spectroscopy (ICP-OES), this article introduces an analysis method enabling the direct quantitative determination of residual template molecules in molecularly imprinted polymer (MIP) matrices. ICP-OES was applied for the determination of residual iodine in MIPs prepared against the iodinated X-ray contrast agent iohexol. Prior to analysis, a microwave-assisted acidic oxidative digestion method was developed simultaneously enabling the digestion of the polymer matrix and the exhaustive oxidation of organically bound iodine. Excellent recovery rates and a high accuracy confirm the feasibility and utility of a microwave-assisted digestion with subsequent ICP-OES analysis for the determination of residual iodine in MIPs, and indicate the potential of this combination as a widely applicable monitoring tool for the efficiency of template extraction from MIP matrices.

Carbon nanotubes (CNTs) have demonstrated outstanding chemical and mechanical stability, electrical properties, and strong interactions with aromatic compounds owing to the π-electron system on the graphene sheets. Taking advantage of these unique properties, we have developed a fully validated sample pre-concentration technique for determination of polychlorinated biphenyls (PCBs) in aqueous environments using gas chromatography combined with a micro-cell electron capture detector (GC-μECD). The optimized method using pristine MWCNTs gave recoveries in the range of 46.0–92.5%, 51.4–91.5%, 48.7–77.8% for tap water, river water, and lake water, respectively. Compared to conventional C18 adsorbent and oxidized MWCNTs (oMWCNTs), pristine MWCNTs provided the best recoveries, thereby confirming that MWCNTs are excellent alternatives for C18, with the ability to achieve high performance. The developed protocol achieved method detection limits in the range of 0.002–0.011 μg L−1 and relative standard deviation (RSD) < 15.5%.

Surface-imprinted polymer particles facilitate the accessibility of synthetic selective binding sites for proteins. Given their volume-to-surface ratio, submicron particles offer a potentially large surface area facilitating fast rebinding kinetics and high binding capacities, as investigated herein by batch rebinding experiments. Polymer particles were prepared with (3-acrylamidopropyl)trimethylammonium chloride as functional monomer, and ethylene glycol dimethacrylate as cross-linker in the presence of pepsin as template molecule via miniemulsion polymerization. The obtained polymer particles had an average particle diameter of 623 nm, and a specific surface area of 50 m2 g−1. The dissociation constant and maximum binding capacity were obtained by fitting the Langmuir equation to the corresponding binding isotherm. The dissociation constant was 7.94 μM, thereby indicating a high affinity; the binding capacity was 0.72 μmol m−2. The binding process was remarkably fast, as equilibrium binding was observed after just 1 min of incubation. The previously determined selectivity of the molecularly imprinted polymer for pepsin was for the first time confirmed during competitive binding studies with pepsin, bovine serum albumin, and β-lactoglobulin. Since pepsin has an exceptionally high content in acidic amino acids enabling strong interactions with positively charged quaternary ammonium groups of the functional monomers, another competitive protein, i.e., α1-acid glycoprotein, was furthermore introduced. This protein has a similarly high content in acidic amino acids, and was used for demonstrating the implications of ionic interactions on the achieved selectivity.