•Best-practice framework for microplastic sampling, sample preparation and analysis.•Beneficial synergies between spectroscopic and thermoanalytical analytical methods.•Use of s surrogate polymer to ...assess removal efficiency.
Wastewater treatment plants (WWTPs) may represent point sources for microplastic discharge into the environment. Quantification of microplastic in effluents of WWTPs has been targeted by several studies although standardized methods are missing to enable a comparability of results. This study discusses theoretical and practical perspectives on best practices for microplastic sampling campaigns of WWTPs. One focus of the study was the potential for synergies between thermoanalytical and spectroscopic analysis to gain more representative sampling using the complementary information provided by the different analytical techniques. Samples were obtained before and after sand filtration from two WWTPs in Germany using cascade filtration with size classes of 5,000 – 100 µm, 100 – 50 µm, and 50 – 10 µm. For spectroscopic methods samples were treated by a Fenton process to remove natural organic matter, whereas TED-GC-MS required only sample extraction from the filter cascade. µFTIR spectroscopy was used for the 100 µm and 50 µm basket filters and µRaman spectroscopy was applied to analyze particles on the smallest basket filter (10 µm). TED-GC-MS was used for all size classes as it is size independent. All techniques showed a similar trend, where PE was consistently the most prominent polymer in WWTP effluents. Based on this insight, PE was chosen as surrogate polymer to investigate whether it can describe the total polymer removal efficiency of tertiary sand filters. The results revealed no significant difference (ANOVA) between retention efficiencies of tertiary sand filtration obtained using only PE and by analyzing all possible polymers with µFTIR and µRaman spectroscopy. Findings from this study provide valuable insights on advantages and limitations of cascade filtration, the benefit of complementary analyses, a suitable design for future experimental approaches, and recommendations for future investigations.
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Soot aerosol, which is a major pollutant in the atmosphere of urban areas, often contains not only carbonaceous matter but also inorganic material. These species, for example, iron compounds, ...originated from impurities in fuel or lubricating oil, additives or engine wear may change the physico-chemical characteristics of soot and hence its environmental impact. We studied the change of composition, structure, and oxidation reactivity of laboratory-produced soot aerosol with varying iron content. Soot types of various iron contents were generated in a propane/air diffusion flame by adjusting the doping amount of iron pentacarbonyl Fe(CO)
5
to the flame. Scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX) was combined with cluster analysis (CA) to separate individual particles into definable groups of similar chemical composition representing the particle types in dependence of the iron content in soot. Raman microspectroscopy (RM) and infrared spectroscopy were applied for the characterization of the graphitic soot structure, hydrocarbons, and iron species. For the analysis of soot reactivity, temperature-programmed oxidation (TPO) was used. It is demonstrated that iron is most dominantly present in the form of amorphous Fe (III) oxide crystallizing to hematite α-Fe
2
O
3
upon thermal treatment. Iron contaminations do not change the soot microstructure crucially, but Fe(CO)
5
doping of the flame impacts hydrocarbon composition. Soot oxidation reactivity strongly depends on the iron content, as the temperature of maximum carbon (di)oxide emission T
max
follows an exponential decay with increasing iron content in soot. Based on the results of the thermo-chemical characterization of laboratory-produced internally mixed iron-containing soot, we can conclude that iron-containing combustion aerosol samples cannot be characterized unambiguously by current thermo-optical analysis protocols.
Copyright 2012 American Association for Aerosol Research
A comprehensive physicochemical characterization of heterogeneous nanoplastic (NPL) samples remains an analytical challenge requiring a combination of orthogonal measurement techniques to improve the ...accuracy and robustness of the results. Here, batch methods, including dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), tunable resistive pulse sensing (TRPS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM), as well as separation/fractionation methods such as centrifugal liquid sedimentation (CLS) and field-flow fractionation (FFF)–multi-angle light scattering (MALS) combined with pyrolysis gas chromatography mass spectrometry (pyGC–MS) or Raman microspectroscopy (RM) were evaluated for NPL size, shape, and chemical composition measurements and for quantification. A set of representative/test particles of different chemical natures, including (i) polydisperse polyethylene (PE), (ii) (doped) polystyrene (PS) NPLs, (iii) titanium dioxide, and (iv) iron oxide nanoparticles (spherical and elongated), was used to assess the applicability and limitations of the selected methodologies. Particle sizes and number-based concentrations obtained by orthogonal batch methods (DLS, NTA, TRPS) were comparable for monodisperse spherical samples, while higher deviations were observed for polydisperse, agglomerated samples and for non-spherical particles, especially for light scattering methods. CLS and TRPS offer further insight with increased size resolution, while detailed morphological information can be derived by electron microscopy (EM)–based approaches. Combined techniques such as FFF coupled to MALS and RM can provide complementary information on physical and chemical properties by online measurements, while pyGC–MS analysis of FFF fractions can be used for the identification of polymer particles (vs. inorganic particles) and for their offline (semi)quantification. However, NPL analysis in complex samples will continue to present a serious challenge for the evaluated techniques without significant improvements in sample preparation.
Graphical abstract
Organic Solid-Solid Wetting Deposition (OSWD) enables the fabrication of supramolecular architectures without the need for solubility or vacuum conditions. The technique is based on a process which ...directly generates two-dimensional monolayers from three-dimensional solid organic powders. Consequently, insoluble organic pigments and semiconductors can be made to induce monolayer self-assembly on substrate surfaces, such as graphene and carbon nanotubes, under ambient conditions. The above factuality hence opens up the potential of the OSWD for bandgap engineering applications within the context of carbon based nanoelectronics. However, the doping of graphene via OSWD has not yet been verified, primarily owing to the fact that the classical OSWD preparation procedures do not allow for the analysis via Raman spectroscopy – one of the main techniques to determine graphene doping. Hence, here we describe a novel approach to induce OSWD on graphene leading to samples suitable for Raman spectroscopy. The analysis reveals peak shifts within the Raman spectrum of graphene, which are characteristics for p-type doping. Additional evidence for chemical doping is found via Scanning Tunneling Spectroscopy. The results open up a very easily applicable, low-cost, and eco-friendly way for doping graphene via commercially available organic pigments.
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Polyhydroxyalkanoates (PHAs), polyphosphate (poly-P) and polysulfide or elemental sulfur (poly-S) are the key functionally relevant polymers involved in the recently reported Denitrifying Sulfur ...conversion-associated Enhanced Biological Phosphorus Removal (DS-EBPR) process. However, little is known about the structural dynamics and storage states of these polymers. In particular, investigating the poly-S generated in this process is quite a superior challenge. This study was thus aimed at simultaneously qualitative-quantitative investigating poly-S and associated poly-P and PHAs through the integrated chemical analysis and Raman micro-spectroscopy coupled with multiple microscopic methods (i.e. optical microscopy, confocal laser scanning microscopy, and differential interference contrast microscopy). The chemical analytical results displayed a stable DS-EBPR phenotype in terms of sulfur conversion, P release/uptake and the dynamics of relevant polymers. The multiple microscopic images and Raman spectrum profiles further clearly demonstrated the existence of the polymers and their dynamic changes under alternating anaerobic-anoxic conditions, consistent with the chemical analytical results. In particular, Raman analysis for the first time unraveled the co-existence of S0/Sn2− species stored either intracellularly or extracellularly; and the dynamic conversions between S0/Sn2− and other sulfur species suggest that there might be a universal pool of bioavailable sulfur. The results reveal the mechanisms underlying the structural dynamics and changes in storage states of the relevant polymers that are functionally relevant to the carbon/phosphorus/sulfur-cycles during different metabolic phases. These mechanisms would otherwise not be obtained only using a traditional chemical analysis-based approach.
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•Relevant polymers (e.g. PHA, poly-P and poly-S) play key roles in DS-EBPR.•Polymers were semi-quantitatively identified by Raman spectra and microscopes.•The dynamics of polymers analyzed by Raman/microscopes matches chemical analysis.•Mixed S0/Sn2− species in bacteria were stored either intra- or extracellularly.
Based on molecular-specific surface-enhanced Raman scattering (SERS) spectroscopy we were able to discriminate between rough and smooth strains of
Escherichia coli
and
Proteus mirabilis
bacteria. For ...this purpose, bacteria have been immobilized through electrostatic forces by inducing a positive charge on the glass slide. This way, SERS spectra on bacterial biomass and also on single bacteria could be recorded in less than 2 h, by using concentrated silver nanoparticles as SERS-active substrate. Single-bacterium SERS spectral fingerprints showed to be sensitive to the presence of the O-antigen at strain level and to the microorganisms growth phase. By using principal component analysis (PCA) on the SERS spectra recorded from
E. coli
and
P. mirabilis
, these two uropathogens could be fairly discriminated.
Micro-Raman spectroscopy (micro-RS) and Temperature Programmed Oxidation (TPO) combined with FTIR gas analysis have been used to determine structural changes and oxidation behavior in samples of ...spark discharge (GfG) and heavy duty engine (EURO IV) soot upon oxidation by oxygen in a temperature range between 293 K and 873 K. Raman spectra of soot and FTIR spectra of oxidation products have been recorded before and during the oxidation process. For micro-RS analysis spectral parameters have been determined by a five band curve fitting procedure (G, D1-D4). For GfG soot the relative intensity of D3 band is decreasing and the two observed Raman peaks are getting more separated during the TPO. This suggests a rapid preferential oxidation of highly reactive amorphous carbon. The decrease of the D1 band width indicates a decrease of chemical heterogeneity and an increase of structural order upon oxidation. Changes in Raman spectroscopic parameters are in good agreement with the behavior of soot during oxidation determined by CO
2
emission with FTIR. In contrast to GfG soot the spectral parameters of EURO IV soot remained mostly unchanged during the oxidation process, so that EURO IV soot shows just minor changes in structure upon oxidation. Overall Raman spectroscopic parameters provide information about changes in structural order of graphitic and amorphous carbon fractions during oxidation and can be used to analyze oxidation readiness of soot. Thus micro-Raman spectroscopy may become a rapid analytical tool for the determination of soot reactivity by analysis of the structure.
We present an immunoassay microarray flow-through system for the surface-enhanced Raman scattering (SERS) analysis of bacteria. The system has been constructed to support and automatize the ...nondestructive in situ analysis of different microorganisms in aqueous environment. After the immobilization of the desired antibodies to an activated PEG-coated surface, the chip is placed into the flow cell which is then flushed with the contaminated sample. Finally, colloidal metal nanoparticles are added and the cells are detected label-free by SERS. Here, we introduce the successful imaging of single microorganisms in the flow cell as well as the quantification of microorganisms in water by SERS mapping with a linear range between 4.3 × 10
3
to 4.3 × 10
5
cells/mL. The method has potential for routine application, e.g. for drinking water control.
We describe a method for the synthesis of SERS-active silver nanoparticles (AgNPs) directly on the surface of bacteria (bacteria@AgNPs), specifically of
E. coli
cells. This straightforward strategy ...allows for the sensitive determination of bacteria on a microarray platform. Antibodies were used as selective receptors on the microarray surface. The Raman signal of bacteria@AgNPs is about 10 times higher than that obtained previously with microarrays based on mixing bacteria and AgNPs (bacteria+AgNPs). The optimum SERS enhancement of bacteria@AgNPs is obtained under 633-nm laser excitation, and this most likely is due to the plasmonic interaction of aggregated AgNPs. The method allows for an identification and quantification even of single
E. coli
bacteria. In our perception, this straightforward approach represents a most valuable tool for the detection of
E. coli
and, conceivably, of other bacteria, and thus has a large potential in environmental monitoring, medical diagnosis, and in food safety and quality control.
Graphical Abstract
Synthesizing AgNPs directly on the surface of bacteria is demonstrated to be a highly efficient approach for a label-free readout of bacteria microarrays by surface-enhanced Raman scattering (SERS), resulting in signals about 10 times higher than previously reported results.
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