Analytische Chemie
Filtern
Dokumenttyp
- Vortrag (16)
- Zeitschriftenartikel (9)
- Sonstiges (3)
- Posterpräsentation (3)
- Forschungsdatensatz (2)
- Beitrag zu einem Sammelband (1)
- Video (1)
Schlagworte
- Nanomaterials (35) (entfernen)
Organisationseinheit der BAM
- 6 Materialchemie (23)
- 6.1 Oberflächen- und Dünnschichtanalyse (14)
- 6.5 Synthese und Streuverfahren nanostrukturierter Materialien (8)
- 1 Analytische Chemie; Referenzmaterialien (6)
- 1.2 Biophotonik (4)
- 1.1 Anorganische Spurenanalytik (2)
- 5 Werkstofftechnik (2)
- 6.3 Strukturanalytik (2)
- 1.4 Prozessanalytik (1)
- 1.6 Anorganische Referenzmaterialien (1)
Eingeladener Vortrag
- nein (16)
The surface modification of nanometer- and micrometer-sized particles with polyethylene glycol (PEG) ligands of varying length is a very common strategy to tune their hydrophilicity and biocompatibility, minimize unspecific interactions, improve biofunctionalization efficiencies, and enhance blood circulation times. Nevertheless, simple methods for the quantification of PEG ligands are rare. This is similarly true for the spectroscopic characterization of lanthanide-doped upconverting nanoparticles (UCNPs), novel near infrared (NIR)-excitable nonlinear fluorescence reporters for bioanalysis and theranostics, providing background-free multiple narrow emission bands in the visible and NIR, excellent photostability, and long luminescence lifetimes.
We present here a simple method for the determination of the number of PEG ligands on nanomaterials and screening methods for the fast identification of nonradiative deaction pathways in UCNPs.
Fluorescent particles like nm- and m-sized polymeric beads doped or labeled with different types of fluorophores and nanocrystalline systems like quantum dots and upconversion phosphors emitting in the visible (vis), near-infrared (NIR), and IR (infrared) region are of increasing importance as fluorescent reporters for bioanalysis and medical diagnostics. The assessment and comparison of material performance and the development of rational design strategies for improved systems requires suitable spectroscopic tools for the determination of signal-relevant optical properties and analytical tools for the determination of the number of surface groups, ligands, biomolecules and /or fluorophores per bead. In this respect, suitable spectroscopic tools for the characterization of the optical properties of such materials like photoluminescence quantum yields and brightness values and the determination of their surface chemistry are introduced. This includes integrating sphere setups for absolute measurements of fluorescence quantum yields of liquid and solid, transparent and scattering materials in the wavelength region of 350 nm to 1600 nm at varying excitation power densities for the study of multi-photon processes and simple optical assays, validated by comparison with established analytical techniques relying on different detection principles. Here, different examples for the optical and analytical characterization of different types of nanoscale reporters are presented.
There is an increasing interest in optical reporters like semiconductor quantum dots and upconversion nanocrystals with emission > 800 nm for bioanalysis, medical diagnostics, and safety barcodes. Prerequisites for the comparison of material performance, the mechanistic understanding of nonradiative decay channels, and the rational design of new nanomaterials with improved properties are reliable fluorescence measurements and validated methods for the assessment of their surface chemistry. The latter is of special relevance for nanocrystalline emitters, where surface states and the accessibility of emissive states by quenchers largely control accomplishable photoluminescence quantum yields and hence, signal sizes and detection sensitivities from the reporter side. Here, we present the design of integrating sphere setups for the excitation power density-dependent absolute measurement of emission spectra and photoluminescence quantum yields in the wavelength region of 350 to 1600 nm and results from spectroscopic studies of semiconductor quantum dots and upconversion nanocrystals of different size and surface chemistries in various environments. Subsequently, examples for simple approaches to surface group and ligand analysis are presented.
The Sponsorship Programme for the Testing of Manufactured Nanomaterials (further referred to as “the Testing Programme”) was concluded in March 2013, and the publication of the dossiers via the OECD website (www.oecd.org/science/nanosafety) started in June 2015. As indicated in the “Guidance manual for the testing of manufactured nanomaterials: OECD’s sponsorship programme”, after conclusion of the Testing Programme a next step is to consider “the status, need for, and coordination of further test development”. Parallel to concluding the final stages of the Testing Programme, a series of workshops have taken place, in which for different topics the applicability of existing OECD test guidelines for nanomaterials was discussed and the need for new ones analysed. One workshop focussed on physico-chemical methods, addressing in detail the relevance of each physico-chemical endpoint proposed in the Testing Programme for the regulation of nanomaterials. The methods were discussed in more general terms. However, as most of the proposed endpoints are new to the OECD Test Guidelines Programme, a much more detailed evaluation of the applied methods would
be highly relevant.
To this extent,the Netherlands volunteered to lead an initial detailed evaluation of the applicability of the test methods applied to determine the physico-chemical properties of different types of nanomaterials in the Testing Programme. This initial focus on physico-chemical properties was prompted by the essential need for an adequate and complete characterisation of nanomaterials to enable a further evaluation of their (toxicological) properties.
A number of experts from several delegations volunteered to review and evaluate the methods applied to determine the physico-chemical properties of the nanomaterials in the Testing Programme.
The Organization for Economic Co-operation and Development (OECD) established the Working Party on Manufactured Nanomaterials (WPMN) in 2006. The OECD-WPMN initiated the "Sponsorship Programme for the Testing of Manufactured Nanomaterials", where a defined set of manufactured nanomaterials is tested for their physical/chemical properties, their toxicological potential and their environmental fade. The results of this program have been declassified in June 2015. Having a big set of independent measurements for one endpoint/measurand, has the advantage of really independent comparision of methods. It is surprising what these few data sets already delivered. Nevertheless the amount of data in the OECD-dossiers is still not enough. While we have a lot of data for titanium dioxide, we have only one data set for zinc oxide and very weak data sets for silver nanoparticles. This limits the useablility of the data sets.
Regarding the quality of the data, we have seen a very good agreement of TEM and SMPS. This leads to the advice that we should have results for these two methods for each nanomaterial in the sponsorship programme.
Another outcome of this draft review is, that currently we cannot compare measurements of agglomerates. This also prohibits the use of DLS as a standard method for size determination.
Coating, stabilization layers, functionalization of particles or simple contamination are common variants of a core-shell system. For smaller nanoparticles this is of major importance. A particle with 16 nm diameter and a usual surface layer of 2 nm will have the same volume for the core as for the shell. In this case the material of the particle doesn’t have a clear definition. It is a common case that a particle consists of four different layers: Core, shell, stabilization layer and contamination. The properties of the particles differ according to this structure. For example silver particles might have a different dissolution rate for pure particles and for particles which are grown on top of a core.
Different solubility or defined other properties of materials is a common reason for producing core-shell systems. Gold cores are surrounded by silica to stabilize them or to get a defined distance between the cores. Silica might be surrounded by gold and the silica dissolved afterwards. This delivers hollow shells. Another important example for core-shell systems are quantum dots. A small core is surrounded by a different material for increasing the photoluminescence. Furthermore there a stabilization layer is needed. The smallest part of the final particles is the initial core. The photoluminescence is based on this core, but the shells contain much more material. Categorization should address this.
Core-shell systems are not covered by most of the existing decision trees for grouping. They are either regarded as special case or a singular layer. This disqualifies core-shell systems for grouping within the common models. There might be a very easy way to avoid this problem and even to combine some of the different decision trees. Starting the decision tree with the solubility of the outer shell and subsequently addressing the inner layers will be a pragmatic approach to solve the problem. If there is no shell, the categorization can start with a tiered approach or with the proposed “stawman” chemical categorization. If a shell is covering the surface there is a need to check if the shell is stable. If it is stable, the particle can be categorized based on this shell. If it is soluble, the ions need to be addressed as in the classic case. Furthermore the shell might increase the uptake by the cells. If the ions and the uptake are not critical the categorization can continue with the next layer.
With this not perfect but pragmatic approach, the surface layers can be addressed with very limited additional efforts. Most criteria are based on classically tabulated data. Including a rating system like the precautionary matrix approach might even address the fact that some parameters are not always Yes/No, e.g. solubility, ion toxicity and uptake.
Spectroscopic methods for the absolute characterization of the optical properties of different types of vis/NIR-emissive nanomaterials like semiconductor quantum dots, upconversion nanocrystals, and dye-doped polymer nanoparticles will be presented and their relevance for the mechanistic understanding of nonradiative decay channels and the rational design of new nanomaterials will be underpinned. In this respect, also the potential of optical spectroscopy for surface group and ligand analysis surface chemistry will be demonstrated.
This study evaluates on the possibility of using gold nanoparticles functionalizedwith the luminol derivative N-(aminobutyl)-N-(ethylisoluminol)(ABEI) and hybridizedwith graphene oxidenanoribbons on acarbon based screen-printedelectrode (ABEI-AuNP-GONR/SPE) as an enzymaticelectrochemiluminescence (ECL) urea sensor.The electrocatalytic activity and ECL intensity of ABEI-AuNP-GONR/SPE were found to increase proportionally with the concentrationofurea in the analyte sample,owing to the rise in pH value.These phenomena are attributed to increased formation of luminol monoanion precursors for further electrochemical oxidation,which in turn produce eitherluminol radicals or excited3-amino-phthalate molecules.The luminescence is most likely caused by the interaction of luminol radicals with superoxide radicals formed from dissolved oxygen. Thesensitivity of our sensor was determinedtobe 170.58 mM@1 and 16.23 mM@1 for urea concentrations from 2to5.82 mM and from 5.82 to 30 mM, respectively, coveringthe normal urea level in human blood.
Development and market introduction of new nanomaterials trigger the need for an adequate risk assessment of such products alongside suitable risk communication measures. Current application of classical and new nanomaterials is analyzed in context of regulatory requirements and standardization for chemicals, food and consumer products. The challenges of nanomaterial characterization as the main bottleneck of risk assessment and regulation are presented. In some areas, e.g., quantification of nanomaterials within complex matrices, the establishment and adaptation of analytical techniques such as laser ablation inductively coupled plasma mass spectrometry and others are potentially suited to meet the requirements. As an example, we here provide an approach for the reliable characterization of human exposure to nanomaterials resulting from food packaging. Furthermore, results of nanomaterial toxicity and ecotoxicity testing are discussed, with concluding key criteria such as solubility and fiber rigidity as important parameters to be considered in material development and regulation. Although an analysis of the public opinion has revealed a distinguished rating depending on the particular field of application, a rather positive perception of nanotechnology could be ascertained for the German public in general. An improvement of material characterization in both toxicological testing as well as end-product control was concluded as being the main obstacle to ensure not only safe use of materials, but also wide acceptance of this and any novel technology in the general public.
Nanomaterials are present in our everyday life. Paint coats, sunscreens, catalysts and additives for tyres are good examples for the use of such materials in mass-market products. The problem of the safety of nanomaterials is recognized as a problem for health and environment, which lead to the special registration of nanomaterials according to an annex of REACH as of 2020. But a great problem for the risk assessment of nanomaterials that several factors could influence the hazardous nature of them. Additional to composition, crystal structure, size and shape the surface properties of such particles belong to these parameters for risk assesment. The reason for the relevance of the surface is obvious: the smaller the particle, the higher is the share of the surface. Additionally, the surface is the region of the particle which interacts with the surrounding which is another crucial factor for the understanding the effect of a nanomaterial on health and environment. In the OECD Testing Programme on Manufactured Nanomaterials exists consequently an Endpoint 4.30 Surface Chemistry in Chapter 4. PHYSICAL AND CHEMICAL PROPERTIES. In summary, there is obviously a need for a correlation between surface chemical analytic data and toxicity. To fill in this gap, we present surface analytic results obtained with X-ray photoelectron spectroscopy and Time-of-Flight Secondary Ion Mass Spectrometry and correlate them with cytotoxic data gain by high-throughput screening experiments. It must be noted, that these experiments were done at the same set of titania materials taken from the JRC (Joint Research Centre of the European Union) Nanomaterials Repository. As material TiO2 was chosen due to its widespread use in consumer products, e.g. paint coats and sunscreens. With this new approach a better understanding of the influence of surface properties on the toxicity can be expected leading to a better risk assessment of these materials.