Ingenieurwissenschaften und zugeordnete Tätigkeiten
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The project ProMoAM is presented. The goal of the project is to evaluate which NDT techniques or combination of techniques is suited for in-situ quality assurance in additive manufacturing of metals. To this end, also 3d-data fusion and visualization techniques are applied. Additional ex-situ NDT-techniques are used as references for defect detection and quantification. Feasability studies for NDT-techniques that are presently not applicable for in-situ use are performed as well.
The presentation gives a brief overview of the whole project and the different involved NDT-techniques.
For metal-based additive manufacturing, sensors and measuring systems for monitoring of the energy source, the build volume, the melt pool and the component geometry are already commercially available. Further methods of optics, spectroscopy and non-destructive testing are described in the literature as suitable for in-situ application, but there are only a few reports on practical implementations.
Therefore, a new BAM project aims to develop process monitoring methods for the in-situ evaluation of the quality of additively manufactured metal components. In addition to passive and active thermography, this includes optical tomography, optical emission and absorption spectroscopy, eddy current testing, laminography, X-ray backscattering and photoacoustic methods. These methods are used in additive manufacturing systems for selective laser melting, laser metal deposition and wire arc additive manufacturing. To handle the sometimes huge amounts of data, algorithms for efficient preprocessing are developed and characteristics of the in-situ data are extracted and correlated to defects and inhomogeneities, which are determined using reference methods such as computer tomography and metallography. This process monitoring and fusion of data of different measurement techniques should result in a significant reduction of costly and time-consuming, destructive or non-destructive tests after the production of the component and at the same time reduce the production of scrap.
Here, first results of simultaneous measurements of optical emission spectroscopy and thermography during the laser metal deposition process using 316L as building material are presented. Temperature values are extracted from spectroscopic data by fitting of blackbody emission spectra to the experimental data and compared with results from a thermographic camera. Measurements with and without powder flow reveal significant differences between welding at a pristine metal surface and previously melted positions on the build plate, illustrating the significant influence of the partial oxidation of the surface during the first welding process on subsequent welding. The measurement equipment can either be mounted stationary or following the laser path. While first results were obtained in the stationary mode, future applications for online monitoring of the build of whole parts in the mobile mode are planned.
This research was funded by BAM within the focus area Material.
Die gemeinsame Forschungsstrategie der Bundesoberbehörden zur Nanotechnologie wurde 2016 veröffentlicht. Die darin enthaltenen Aufgaben wurden von den Bundesoberbehörden vielfältig bearbeitet. Diese Präsentation gibt einen Überblick über die Projekte, die von der BAM bis 2019 bearbeitet wurden/werden und sich in den Rahmen der Forschungsstrategie einordnen.
BAM provides leading expertise in preparation, characterisation and application of fluorescent reference standards and biomedical relevant nanomaterials, as well as in traceable, absolute, and quantitative fluorometric measurements of transparent and scattering systems in the ultraviolet, visible, and near infrared spectral region. BAM will prepare solid low-RI particles in WP1, will develop reference methods to determine the fluorescence intensity and RI of reference materials in WP2, and will measure the fluorescence intensity of EVs in biological test samples of WP3.
Spectral encoding of cells or particles and the discrimination of multiple spectral codes are a critical process in flow cytometry (FCM). Typical issues in spectral encoding are, e.g., the spectral overlap of codes, or the increasing complexity of instruments . The exploitation of the photoluminescence lifetime (LT) as an encoding parameter could be used to circumvent both of these issues, as it adds another dimension to the parameter space, or, when used as a stand-alone parameter, requiring only one excitation light source and one detector. While LT encoding was considered already decades ago it is still not implemented as a routine technique in FCM yet, mainly due to the challenge of very few photons being available within the limited transition time of a cell or particle through the laser spot.
Recently, we demonstrated LT-FCM based on luminophores with ns LTs in a compact and low-cost flow cytometer. Measurements on polymer microbeads containing luminophores with distinctly different excited state LTs enabled the complete discrimination of three LT codes and five codes in total could be identified.
Now, we have extended our approach towards considerably longer LTs by custom-made polymer microbeads loaded with different ratios of InP/ZnS and AgInS2 quantum dots. The use of these materials significantly expands the usable time range for LT encoding to up to several hundred ns. Our studies demonstrate the possibility to further increase the number of viable LT codes for multiplexing in LT-FCM without the need for extensive hardware modifications.
Peptide-polymer bioconjugates combine oligopeptides with synthetic polymer blocks and can be used for various applications in material sciences. In recent years, bioconjugates were applied as compatibilizers and coatings. Biocombinatorial approaches, such as phage display, have been shown to yield strong binding peptides, which exhibit excellent coating properties as peptide-PEO conjugates. Phage display represents a widely exploited strategy to select peptides or proteins that exhibit highly specific affinity to various substrates. Following a phage display experiment, DNA sequencing of binding phage clones is required in order to get the sequence information of the binding peptides. Traditionally, random clone picking followed by Sanger sequencing was applied. However, this method may not necessarily identify the strongest binding clones. Next-generation sequencing made sequencing of whole phage libraries possible, which highly improved the selection of strong binders. Here, we show that the biocombinatorial method of phage display combined with next generation DNA sequencing of whole phage libraries represents a powerful tool for an application in material chemistry. Phage display is used to find specific target binding peptides for polypropylene surfaces (PP). PP binders are of particular interest because thus far gluing or printing on PP is challenging due to its low surface energy. Scripts for sequence data analysis were developed and promising sequences were synthesized as peptide-PEO conjugates. Fluorescence based adsorption experiments on PP surfaces led to the identification of strong binding sequences and a better understanding of the peptide-surface interactions.
In den vergangen Jahren hat das Umweltbewusstsein in der Bevölkerung stark zugenommen und somit auch das Interesse an der Vermeidung von anthropogenen (Schad-)Stoffen in der Umwelt. Eine (neue) Substanzklasse, deren Umweltauswirkungen noch nicht vollständig untersucht sind und die in den vergangenen Jahren immer mehr an Bedeutung gewonnen hat, sind (metallbasierte) Nanomaterialien. Im Gegensatz zu bspw. Elementspezies weisen Nanomaterialien eine Vielzahl von Eigenschaften auf und lassen sich nicht über nur ein Merkmal beschreiben - dies stellt eine große analytische Herausforderung dar. Hier haben sich vor allem die Feld-Fluss-Fraktionierung (AF4) und die single-particle-ICP-MS als leistungsstarke analytische Methoden herausgestellt. In (aquatischen) Umweltmatrizes (z.B. Oberflächengewässern) liegen neben artifiziellen auch natürliche Partikel vor, was eine weitere große Herausforderung für den Nachweis von Nanomaterialien darstellt.
Neben dem Nachweis von anthropogenen Stoffen in der Umwelt ist zudem deren ökotoxikologische Bewertung wichtig. In der aquatischen Ökotoxikologie werden hierzu Testorganismen mit den jeweiligen Substanzen über die Wasserphase exponiert. Effektkonzentrationen (EC50) werden dabei auf Basis der Konzentrationen in der Wasserphase abgeleitet - tatsächlich bioakkumulierte Mengen werden hierbei jedoch meist nicht ermittelt; eine weitere große Herausforderung besteht zudem in der Bewertung von Mischungstoxizitäten. Gängige Testorganismen sind u.a. Kieselalgen (Diatomeen). Diatomeen stehen am Anfang der Nahrungskette - toxikologisch relevante Metalle/Nanomaterialien können sich hierüber im Nahrungsnetz der Oberflächengewässer anreichern und ggf. nachhaltig auswirken.
Im ersten Teil des Vortrages werden zunächst neue elementanalytische Methoden zum Nachweis von metallbasierten Nanopartikeln in Umweltmatrizes auf Basis der AF4/ICP-SFMS sowie stabilen Isotopenlabeln am Beispiel von Eisennanopartikeln vorgestellt.
Im zweiten Teil wird eine neue elementanalytische Methode als komplementäre Technik zur ökotoxikologischen Bewertung von (Schad-)Stoffen vorgestellt. Die neue Methode basiert auf der on-line Kopplung von HPLC mit der single-cell-ICP-(ToF)-MS (sc-ICP-(ToF)-MS) [1, 3-5]. Hierüber konnten wir erfolgreich die automatisierte Multielementanalytik einzelner Diatomeen realisieren und zur Analyse von mit Metallen inkubierten Diatomeen (cyclotella meneghiniana) einsetzen. Wir konnten zeigen, dass die sc-ICP-ToF-MS zukünftig eine leistungsstarke, komplementäre Technik in der aquatischen Ökotoxikologie zum z.B. Test von Metallen und Nanomaterialien darstellt.
Bioanalytical, diagnostic, and security applications require the fast and sensitive determination of a steadily increasing number of analytes or events in parallel in a broad variety of detection formats.[1,2] Ideal candidates for spectral encoding and multiplexing schemes are luminescent nanocrystals like semiconductor quantum dots (QDs), particularly Cd-containing II/VI QDs with their narrow and symmetric emission bands. With the availability of relatively simple and inexpensive instrumentation for time-resolved fluorescence measurements, similar strategies utilizing the compound-specific parameter fluorescence lifetime or fluorescence decay kinetics become increasingly attractive.[3-5] The potential of different types of QDs like II/VI, III/V and Cd-free ternary QDs such as AgInS (AIS) QDs for lifetime-based encoding and multiplexing has been, however, barely utilized, although the lifetimes of these nanocrystals cover a time windows which is barely accessible with other fluorophores. Here we present a brief insight into the photophysics of AIS QDs and show the potential of dye- and QD-encoded beads for lifetime-based encoding and detection schemes in conjunction with flow cytometry and fluorescence lifetime imaging microscopy
Photoluminescence applications in the life and material sciences require bright molecular and nanocrystalline emitters, stimuli-responsive optical probes, signal enhancement, multiplexing, and barcoding strategies and traceable methods to quantify the signal-relevant optical properties of luminescent materials at the ensemble and single molecule/particle level. In this context, current research at Division Biophotonics of BAM is presented ranging from dye and nanocrystal photophysics, absolute measurements of photoluminescence quantum yields in the UV/vis/NIR/SWIR, lifetime multiplexing, and the development of different types of fluorescence standards for validating optical-spectroscopic measurements.
The rational synthesis and use of nanomaterials require the characterization of many different properties, ranging from particle size and size distribution over surface chemistry to more applicationrelevant features like optical, electrochemical, and magnetic properties. In the following, several methods for the characterization of functional groups on nanomaterials, like polymer and silica nanoparticles, semiconductor quantum dots, and lanthanide-based upconversion nanocrystals are presented. Additionally, procedures for the measurement of the key spectroscopic performance parameters of nanomaterials with linear and nonlinear photoluminescence, such as the photoluminescence quantum yield, are presented for the UV/vis/NIR/SWIR.
The comparison of different emitter classes and the rational design of the next generation of molecular and nanoscale reporters require accurate and quantitative photo-luminescence measurements. This is of special importance for all photoluminescence applications in the life and material sciences and nanobiophotonics. In the following, procedures for the determination of the spectroscopic key parameter photoluminescence quantum yield, i.e., the number of emitted per absorbed photons, in the UV/vis/NIR/SWIR are presented including pitfalls and achievable uncertainties and material-specific effects related to certain emitter classes are addressed.
Correlating the photoluminescence (PL) properties of nanomaterials like semiconductor nanocrystals (QDs) and upconversion nanocrystals (UCNPs) assessed in ensemble studies and at the single particle level is increasingly relevant for applications of these nanomaterials in the life sciences like bioimaging studies or their use as reporters in microfluidic assays. Here we present a comparison of the spectroscopic properties of ensembles and single emitters for QDs like II/VI QDs and cadmium-free AIS/ZnS QDs as well as different UCNPs. The overall goal of this study was to derive particle architectures well suited for spectroscopic and microscopic applications.
Relative and Absolute Methods for Measuring Photoluminescence Quantum Yields of UV/vis/NIR Emitters
(2019)
One of the key spectroscopic performance parameters of molecular and particulate emitters is the photoluminescence quantum yield (PL QY) that provides a direct measure for the number of emitted per absorbed photons. This triggered the interest in methods suitable for measuring this property for emitters in various environments in the UV/vis/NIR and above 1000 nm as well as on the ensemble and single emitter level. Moreover, for nonlinear emitters like lanthanide-based upconversion nanocrystals methods including instrumentation for power density-dependent PL QY studies are required.
An overview of the research activities in Division Biophotonics of BAM is given and suitable relative and absolute methods for the deter-mination of PL QY of organic dyes and different types of application-relevant nanomaterials in dispersion and in the solid state are presen-ted. This covers also the design and calibration of integrating sphere setups, achievable uncertainties, and candidates for PL QY reference materials.
Surface functionalization of 2D- and 3D-supports and nanomaterials are nowadays at the core of many applications of functional materials in the life and material sciences. Examples range from membranes and microarrays over bead-based assays, immunoseparation, and next generation sequencing to nanometer-sized optical reporters, nanosensors, and magnetic and optical contrast agents. Typically performed functionalization procedures include silanization and grafting reactions with reactive monomers to introduce functional groups like amino or carboxylic acid groups and the attachment of ligands like polyethylene glycol (PEG) molecules and biomolecules such as peptides, proteins, and DNA.[1-3]
We present here a versatile concept to quantify the number of bioanalytically relevant functional groups like carboxyl, amino, and aldehyde moieties through the specific binding and subsequent release of small reporter molecules such as fluorescent dyes and non-fluorescent chromophores utilizing cleavable linkers or the formation of cleavable bonds as a reversible covalent labeling strategy. This is representatively demonstrated for different types of nano- and microparticles with different labeling densities of carboxyl, amino, and aldehyde groups. This strategy enables to separate the signal-generating molecule from the bead surface, thereby circumventing uncertainties associated with light scattering, binding-induced changes in reporter fluorescence, and fluorescence quenching dye-dye interactions on crowded material surfaces.[1-3] Moreover, the reporters are chosen to be detectable with different analytical methods as prerequisite for straightforward validation via method compari-sons and mass balances. Applications of these assays and multimodal cleavable probes range from a quantitative comparison of bead batches and process control to a qualitative prediction of the coupling efficiencies in bioconjugation reactions.
Different types of optical spectroscopies are introduced with special emphasis on method-inherent limitations and reliable instrument calibration and performance validation. In addition, procedures for the determination of spectroscopic key parameters like the photoluminescence quantum yield are presented including required instrument calibrations and material-specific effects related to certain emitters.
Neuartige Materialien, die bekannte (Werk-)Stoffe mit neuen Funktionalitäten ausstatten, spielen eine zunehmend wichtige Rolle im Bereich der Materialforschung und -prüfung. Das Spektrum neuartiger Materialien reicht von der gezielten Oberflächenfunktionalisierung und -strukturierung makroskopischer Materialien, dünnen Beschichtungen bis hin zu mikro- und nanoskaligen Kompositmaterialien und funktionalen Materialien an der Schnittstelle zur Biologie, Biotechnologie, nachhaltige Energiespeicherung und Sensorik. Dabei bieten neuartige Materialien die Chance, Werkstoffe und Produkte mit erweiterter oder verbesserter Funktionalität zu erhalten und Sicherheit bereits im Designprozess zu berücksichtigen. Durch dieses breite Anwendungsspektrum und die Herausforderungen, die solche Materialien für die Sicherheit in Chemie und Technik mit sich bringen, sind diese in allen Themenfeldern der BAM repräsentiert (Material, Analytical Sciences, Energie, Infrastruktur und Umwelt).
Die Aufgaben der BAM erstrecken sich dabei von der Herstellung von Referenzmaterialien für Industrie, Forschung und Regulation, über die Erstellung von standardisierten Referenzverfahren für nachhaltige Messungen im Umwelt- und Lebenswissenschaftsbereich bis hin zur Bereitstellung von belastbaren und zitierbaren Referenzdaten. Durch die genaue Charakterisierung neuartiger Materialien können potentiell problematische Substanzen identifiziert und deren Risiken besser abgeschätzt werden. In diesem Beitrag werden einige aktuelle Beispiele aus diesen Bereichen vorgestellt.
What isotopes can do...
(2019)
Semiconductor nanocrystals (quantum dots, QDs) are well known for their superior photophysical properties and enabled advancements in several key technologies of the 21st century and numerous technological applications. However, the most studied II-VI semiconductor nanocrystals contain the toxic heavy metal element cadmium, which is limiting their utilization in commercial applications. This has drawn the interest to alternative materials with less toxicity but having similar photophysical features.
The newest generation of TV screens based on QDs have shown that there is a promising environmentally friendly alternative with similar optoelectronic properties, namely indium phosphide (InP) QDs. InP QDs possess a bulk band gap of 1.35 eV with an exciton Bohr radius of ca. 10 nm and thus allow to tune their photoluminescence (PL) from the visible to the near-infrared. Tuning the size and shape of InP QDs and thus tailor their optoelectronic properties can be achieved by different strategies, which range from different types and concentrations of precursors, synthesis temperature or post-synthetic manipulations like etching. The incorporation of other elements like Gallium within the InP core synthesis is another possibility. Using a GaP intermediate layer before growing a ZnS shell has been shown to increase the PL quantum yield, which has been attributed to reduced lattice strain and the removal of phosphor vacancies. Different Ga precursors were investigated but a thorough investigation in terms of their reactivity, localization in the QD and influence on the photophysical properties is lacking to date.
In this contribution we will present the detailed investigation of the presence of two different Ga precursors within the InP core synthesis. Photophysical characterizations (steady-state and PL life-time measurements), transmission electron microscopy, XRD and EDX gave insights into the reactivity of the Ga precursors, the Ga localization in the InP core and influences on the photophysical properties. The variation of the precursor and surfactant concentration and the utilization of different ligands for the Ga precursor allowed tuning the PL emission towards the blue or the red. Depending on the used precursor type we observed the formation of larger-sized InP/GaP core/shell nanocrystals or the formation of InGaP alloy structures enabling to assess the blue range of emission (475 nm).