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Paper des Monats
- ja (2)
The mechanism of action of zirconium permanent modifiers on graphite surfaces was investigated in order to understand its influence on the analytical signal in atomic and molecular absorption spectrometry (AAS/MAS). For this, the molecule formation of CaF was studied, which is used for the indirect analytical determination of fluorine in high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GFMAS). The kinetics of this reaction was established by monitoring its molecular spectrum at different atomisation temperatures. An Arrhenius plot showed a pseudo-first order reaction with respect to fluorine (n = 1). An intermediate state was isolated, and its structure was elucidated by spectroscopic methods: scanning electron microscopy with energy dispersive X-ray spectroscopy (SEMEDX), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XANES and EXAFS), and Raman microspectroscopy. We propose here a mechanism, where ZrO2 acts as a heterogeneous catalyst: after a pyrolytic step, an intermediate state of ZrO(OCaF) is activated, and at higher temperatures, CaF(g) is released from the zirconium-coated graphite surface. No evidence of the formation of zirconium carbide was found. Consequently, as the CaF formation is catalysed by a heterogeneous catalyst, surface modifications with ZrO2 nanoparticles and ZrO xerogels were investigated in order to increase the surface area. Their influence was evaluated in the molecule formation of CaF, CaCl, CaBr, and CaI. Graphite furnace modification with zirconium oxide nanoparticles proves to be the best choice for fluorine analysis with a signal enhancement of more than eleven times with respect a non-coated graphite furnace. However, the influence of zirconium modifications in the analytical signals of Cl, and I is lower than the F signals or even negative in case of the Br. Understanding zirconium modifiers as heterogeneous catalysts offers a new perspective to AAS and MAS, and reveals the potential of surface analytical methods for development of improved permanent modifiers and graphite furnace coatings.
Alkaline earth metal fluoride nanoparticles have been investigated for application in wood protection. Sols of MgF2 and CaF2 were synthesized and their efficacy was tested against fungi and termites (Rehmer 2016, Krahl et al. 2016). The sols were characterized by XRD and SEM. The wood specimens were vacuum impregnated with nanoparticles and then exposed to fungi and termites according to EU certified test conditions. Our results show that wood impregnated with metal fluoride nanoparticles significantly reduce cellulose hydrolysis by fungi and termites. The wood samples were exposed to brown-rot fungi; Coniophora puteana and Poria placenta. Between the two fungi, the overall mass lost due to fungal degradation was lower for treated (MgF2 and CaF2) wood samples exposed to Coniophora puteana. Thus, the metal fluoride nanoparticles impregnated in the wood samples were more efficient in reducing cellulose degradation from Coniophora puteana than from Poria placenta. However the mass loss in samples treated with MgF2 was similar to those treated with CaF2, irrespective of type of fungi. Therefore, it is likely that fungal degradation in treated samples was dependent on the biocidal action of fluorides rather than on the differences in chemical and physical properties of MgF2 and CaF2, respectively. Conversely, for termite exposure, wood samples treated with MgF2 had lower cellulose degradation compared to those treated with CaF2. A possible explanation for this difference in results could be fungi and termites use separate mechanisms for cellulose hydrolysis which will be further investigated. Future experiments include testing the leaching potential of MgF2 and CaF2 nanoparticles from wood. The results from the leaching experiment will test if metal fluoride nanoparticles can provide long-term and environmentally safe protection to wood.
Sol-gel synthesis was used to prepare nanoparticles of MgF2 and CaF2. These nanoparticles were tested for their application in wood protection. In comparison to control samples, wood specimens treated with MgF2 and CaF2 showed lower mass loss under exposure to termites and fungi. Samples treated with MgF2 performed better at protecting wood from cellulose degradation when exposed to termites. Conversely, in the presence of fungi, mass loss in treated samples was similar irrespective of the chemical composition (MgF2 and CaF2) of the treatment. A possible explanation for this difference in results between termites and fungi could be their different mechanism of cellulose hydrolysis. Thus, future wood preservatives would need to be customized according to their specific application.
In this study, a new reliable, economic, and environmentally-friendly one-step synthesis is established to obtain carbon nanodots (CNDs) with well-defined and reproducible photoluminescence (PL) properties via the microwave-assisted hydrothermal treatment of starch and Tris-acetate-EDTA (TAE) buffer as carbon sources. Three kinds of CNDs are prepared using different sets of above mentioned starting materials. The as-synthesized CNDs: C-CND (starch only), N-CND 1 (starch in TAE) and N-CND 2 (TAE only) exhibit highly homogenous PL and are ready to use without need for further purification.
The CNDs are stable over a long period of time (>1 year) either in solution or as freeze-dried powder. Depending on starting material, CNDs with PL quantum yield (PLQY) ranging from less than 1% up to 28% are obtained. The influence of the precursor concentration, reaction time and type of additives on the optical properties (UV-Vis absorption, PL emission spectrum and PLQY) is carefully investigated, providing insight into the chemical processes that occur during CND formation. Remarkably, upon freeze-drying the initially brown CND-solution turns into a non-fluorescent white/slightly Brown powder which recovers PL in aqueous solution and can potentially be applied as fluorescent marker in bio-imaging, as a reduction agent or as a photocatalyst.
Volume specific surface area (VSSA) by BET: concept and demonstration on industrial materials
(2017)
Volume specific surface area (VSSA) as measured by BET constituites a simple and reliable solution to (most) powders. Porous, coated, polydisperse/multimodal materials are to be treated with care, i.e. doubled by analysis with electron microscopy or more advanced BET analysis (e.g. t-plot)for each material in part.
We discuss the role of the volume specific surface area (VSSA) as determined from the specific surface area measured by the (extended) Brunauer-Emmett-Teller (BET) technique, in the identification process of powdered nano- and non-nanomaterials in line with the EU definition of nanomaterial. Results obtained in the NanoDefine project demonstrate that under appropriate conditions, VSSA can be used as proxy to the number-based particle size distribution. The extent of agreement between nano/non-nano classification by electron microscopy (EM) and classification by VSSA is investigated systematically on a large set of diverse particulate substances, representing most of the cases expected in regulatory practice. Thus, parameters such as particle shape, size polydispersity/multi-modality, and particle (inner or coating) porosity are evaluated. Based on these results, we derive a tiered screening strategy for powders, involving the use of VSSA for the purpose of implementing the definition of nanomaterial, and recommend it for inclusion in a technical guidance for the implementation of the definition.
The progress in activities on Microbeam Analysis under VAMAS/TWA 37 is reviewed. Particularly the liaison with the new projects within the ISO technical committee TC 202 is presented and discussed with respect to the possibility of identifying and launching related VAMAS projects. Need of more promotion for the engagement of more participants from industry and academia at national, European and international level is highlighted. Also, the competition with the other technical working areas (on 'nano' or materials-related) is critically discussed. Further, a short overview of the VAMAS areas of activities is given where Germany is involved.
Following points are presented and discussed: i) nPSize as an EMPIR project on the nanoparticle size and shape distribution of (more) complex particles including sample preparation and machine learning approaches; ii) parallel development of ISO 21363 (PSSD by TEM), ISO 19749 (PSSD by SEM), ISO 22292 (3D TEM), ISO 52408 (NP Prep for AFM and EM), iii) VAMAS and pre-standardisation, TWA 34 „Nanoparticle Populations“ with two nPSize ILC projects P15 & P16 – results to be published and integrated in ISO 21363 (PSSD by TEM); iv) Remaining challenges: platelets, 2D materials (TiO2 and GR2M); v) Reference data sets as part of a complete Characterisation Workflow.
Time-gated Förster resonance energy transfer (TG-FRET) between Tb complexes and luminescent semiconductor quantum dots (QDs) provides highly advantageous photophysical properties for multiplexed biosensing. Multiplexed Tb-to-QD FRET immunoassays possess a large potential for in vitro diagnostics, but their performance is often insufficient for their application under clinical conditions. Here, we developed a homogeneous TG-FRET immunoassay for the quantification of carcinoembryonic antigen (CEA), neuron-specific enolase (NSE), and prostatespecific antigen (PSA) from a single serum sample by multiplexed Tb-to-QD FRET. Tb–IgG antibody donor conjugates were combined with compact QD-F(ab’)2 antibody acceptor conjugates with three different QDs emitting at 605, 650, and 705 nm. Upon antibody–antigen–antibody Sandwich complex formation, the QD acceptors were sensitized via FRET from Tb, and the FRET ratios of QD and Tb TG luminescence intensities increased specifically with increasing antigen concentrations.
Although limits of detection (LoDs: 3.6 ng/mL CEA, 3.5 ng/mL NSE, and 0.3 ng/mL PSA) for the triplexed assay were slightly higher compared to the single-antigen assays, they were still in a clinically relevant concentration range and could be quantified in 50 μL serum samples on a B·R·A·H·M·S KRYPTOR Compact PLUS clinical immunoassay plate reader. The simultaneous quantification of CEA, NSE, and PSA at different concentrations from the same serum sample demonstrated actual multiplexing Tb-to-QD FRET immunoassays and the potential of this technology for translation into clinical diagnostics.
Dielectric, anti-reflective or high reflective systems consist of low and high refractive index layers. Common systems are oxides. The preparation of low refractive index MgF2-films of optical quality by means of an anhydrous low temperature solgel synthesis is presented. The MgF2-sol is prepared by spin-coating on silicon and glass substrates. Various film thicknesses between 20 nm and 435 nm have been deposited. It has been shown that the thickness increase is proportional to the number of coating steps. The deposited MgF2-films consist of 10 nm to 20 nm large nanoparticles and have smooth surfaces with an average roughness (Ra) of (1.7 ± 0.3) nm. The optical constants n and k of the films are in agreement with the literature data of bulk-MgF2.
Die Bestimmung der Nanopartikelgrößen- und -formverteilung nach OECD TG 125 mit der Transmission and Scanning Electron Microscopy (SEM/TEM) wird punktuell vorgestellt:
- Generelles Messprinzip
- Beispiele
- Korrelative Mikroskopie
- Welchen Durchmesser misst die Methode?
- Welche Partikel kann diese Methode messen?
- Welche Informationen kann diese Methode liefern?
- Wo stößt die Methode an ihre Grenzen?
- Implementierung und Datenauswertung,
- Reporting.
Anschließend wurde eine Q&A-Session für die Imaging-Methoden organisiert.
The synthesis of TiO2 nanoplatelets with fluorine-containing reactants is carried out using titanium (IV) butoxide as precursor and concentrated HF as shape controller, the final product requires a working up in order to eliminate or at least to reduce the amount of residual fluorides, which is realized here by well-defined thermal treatment of the samples. Bulk and surface sensitive methods namely scanning electron microscopy with energydispersive X-ray spectroscopy (SEM-EDX), Auger electron spectroscopy (AES) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) have been applied to trace the presence of any fluorides in dependence on different information depths and measurement sensitivities of these methods.
The design of comparatively simple and modularly configurable artificial systems able to communicate through the exchange of chemical messengers is, to the best of our knowledge, an unexplored field. As a proof-of-concept, we present here a family of nanoparticles that have been designed to communicate with one another in a hierarchical manner. The concept involves the use of capped mesoporous silica supports in which the messenger delivered by a first type of gated nanoparticle is used to open a second type of nanoparticle, which delivers another messenger that opens a third group of gated nanoobjects. We believe that the conceptual idea that nanodevices can be designed to communicate with one another may result in novel applications and will boost further advances towards cooperative systems with complex behavior as a result of the communication between simple abiotic individual components.
Metal nanoparticles have a substantial impact across diferent felds of science, such as photochemistry, energy conversion, and medicine. Among the commonly used nanoparticles, silver nanoparticles are of special interest due to their antibacterial properties and applications in sensing and catalysis. However, many of the methods used to synthesize silver nanoparticles often do not result in well-defned products, the main obstacles being high polydispersity or a lack of particle size tunability. We describe an automated approach to on-demand synthesis of adjustable particles with mean radii of 3 and 5 nm using the polyol route. The polyol process is a promising route for silver nanoparticles e.g., to be used as reference materials. We characterised the as-synthesized nanoparticles using small-angle X-ray scattering, dynamic light scattering and further methods, showing that automated synthesis can yield colloids with reproducible and tuneable properties.
In this contribution different ways are explored with the aim to generate suitable training data for ‘non-ideal’ samples using various approaches, e.g., computer-generated images or unsupervised learning algorithms such as generative adversarial networks (GANs). We used these data to train simple CNNs to produce segmentation masks of SEM images and tested the trained networks on real SEM images of complex nanoparticle samples. The novel use of CNN for the automated analysis of the size of nanoparticles of complex shape and with a high degree of agglomeration has proved to be a promising tool for the evaluation of particle size distribution on a large number of constituent particles. Further development and validation of the preliminary model, respectively larger training and validation data sets are necessary.
In this contribution different ways are explored with the aim to generate suitable training data for ‘non-ideal’ samples using various approaches, e.g., computer-generated images or unsupervised learning algorithms such as generative adversarial networks (GANs). We used these data to train simple CNNs to produce segmentation masks of SEM images and tested the trained networks on real SEM images of complex nanoparticle samples. The novel use of CNN for the automated analysis of the size of nanoparticles of complex shape and with a high degree of agglomeration has proved to be a promising tool for the evaluation of particle size distribution on a large number of constituent particles. Further development and validation of the preliminary model, respectively larger training and validation data sets are necessary.
Most industrial nanoparticles have non-spherical shapes and also possess polydisperse size distributions, and due to their agglomeration/ aggregation state are difficult (or even impossible) to be addressed individually. Further, driven by regulatory purposes related to the identification of a material as a nanomaterial, the accurate measurement of the smallest dimension of a (nano)particulate material makes the analysis even more complex.
In the first phase of the EU Project nPSize - Improved traceability chain of nanoparticle size measurements (https://www.bam.de/Content/DE/Projekte/laufend/nPSize/npsize.html), the efforts are focused on synthesis of nanoparticles of well-defined, non-spherical shape. Following candidates of reference materials (CRM) with certifiable particle size (distribution) are under characterization with respect to their homogeneity and stability: (i) titania nanoplatelets (10-15 nm thickness x 50-60 nm lateral), (ii) titania bipyramides (~60 nm length x 40 nm width), (iii) titania acicular particles (100 nm length x 15-20 nm width; aspect ratio 5.5/6), (iv) gold nanorods (~10 nm width x 30 nm length), and (v) gold nanocubes (~55 nm x 55 nm x 55 nm).