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Mandatory for the comparison of different emitter classes and the rational design of the next generation of molecular and nanoscale reporters are reliable and quantitative photoluminescence measurements. This is of special relevance for all fluorescence applications in the life and material sciences. In the following, proccedures for the determination of this spectroscopic key parameter are presented including material-specific effects related to certain emitters
Development of analytical method and certified reference material for zearalenone in edible oils
(2017)
Quality and safety of food products require their reliable analysis. Contaminants, in particular mycotoxins, are key-components for food safety. About 25 % of the world's food crops are contaminated with mycotoxins posing a severe health risk to humans. In order to strengthen food safety and consumer protection the European Commission (EC) set maximum levels for priority mycotoxins in certain foods for human consumption. In 2013, the EC and CEN (European Committee for Standardization) started an initiative to standardize analytical methods for mycotoxins in food which gained increasing relevance, e.g. zearalenone (ZEN).[1] ZEN, an estrogenic mycotoxin produced by several Fusarium species, contaminates cereal crops worldwide. Due to its lipophilic nature ZEN is often found in edible oils (particularly in maize germ oils) derived from contaminated plants. Therefore, an European maximum level of 400 µg/kg is currently in force.[2] To perform reliable food analysis a sustainable metrological infrastructure is of major importance enabling the quantification of priority mycotoxins (here: ZEN). To achieve this goal an integrated approach is needed targeted at the development of validated analytical methods and certified reference materials (CRM).
A highly selective method for ZEN in edible oils will be presented, based on solid phase extraction (SPE) using hydrazine-functionalized particles. This method was developed for manual application using commercial SPE cartridges as well as for automated SPE-HPLC online coupling. While ZEN is covalently coupled to the solid phase by means of a hydrazone bond, undesired matrix components can be removed very efficiently. Finally, ZEN is decoupled from the solid phase, leading to highly purified extracts which are measured by HPLC-FLD.
The development of the first European Reference Material (ERM®) for ZEN in maize germ oil (ERM®-BC715) will be presented and discussed. This ERM®-project underpins the urgent need for mycotoxin-CRMs to support food safety and public health.
[1] European Commission (EC) Mandate M/520 (2013) for standardisation addressed to CEN for methods of analysis for mycotoxins in food. [2] Commission Regulation (EC) No 1126/2007 amending Regulation (EC) No 1881/2006 setting maximum levels for certain contaminants in foodstuffs as regards Fusarium toxins in maize and maize products.
Creating the Silver Standard: Development of a Silver Nanoparticle Reference Material using SAXS
(2017)
The utilization of silver nanoparticles in consumer related products has significantly increased over the last decade, especially due to their antimicrobial properties. Today they are used in a high variety of products, which ranges from food containers over children toys and textiles. Therefore, research on the toxicological potential of silver in a nanoscale form becomes increasingly important for a high amount of studies. Unfortunately the results of these studies are extremely diverse and do not lead to a consistent evaluation of the toxicity of silver nanoparticles. The central problem lies in the use of a wide range of silver nanoparticles, which show a broad size distribution. To overcome this problem we report on the synthesis of ultra-small silver nanoparticles and their quantitative characterization by small-angle X-ray scattering. The particles are highly stable and show no aggregation for more than six months. SAXS analysis via a Monte Carlo data evaluation procedure reveal a narrow size distribution of the silver cores with a mean volume weighted radius of 3.0 nm and a distribution width of 0.6 nm. Dynamic light scattering provides a hydrodynamic radius of 10.0 nm and a PDI of 0.09. The particles are stabilized with poly(acrylic acid) (PAA) forming a shell with a thickness of 7.0 nm. It is foreseen to use these thoroughly characterized particles as reference material to compare the catalytic and biological properties of functionalized silver nanoparticles. As a first step the particles are used in the first world-wide inter-laboratory comparison of SAXS. This study reveals that SAXS shows highly reproducible results for particles in the sub-20 nm region independently on the type of instrument used. Furthermore, the stabilizing ligand PAA can be easily exchanged by biomolecules to modify the surface functionality. Replacements of PAA with glutathione (GSH) and bovine serum albumin (BSA) have been performed as examples. With this flexible system first applications regarding biological application in an artificial digestion procedure have been performed. Thereby the changes in size distribution and aggregation state were monitored by SAXS.
Emission testing of products is currently a rapidly increasing field of measurement activity. Labelling procedures for construction products are based on such emission test chamber measurements and hence measurement performance should be verified. A suited procedure for this purpose is the testing of one unique homogenous material in different laboratories within a Round Robin Test (RRT). Therefore, it is useful to have a reference material which can be used within inter-laboratory studies or as part of the quality management system to ensure comparable results. Several approaches on the development of reproducibly emitting materials have been published. These have in common only to emit a single VOC – toluene. Two further research studies carried out by BAM aimed to develop reference material for emissions testing containing one or more VOC in a single material. The first approach was a doped lacquer with Volatile and Semi-Volatile Organic Compounds (VOC/SVOC) and the second was Thermoplastic Polyurethane (TPU) or a Squalane/Paraffin mixture. Results received with the lacquer based material were presented in more detail.
Since some volatile organic compounds (VOC) are
dangerous to human health whilst others cause harm to the environment by influencing the oxidative capacity of the atmosphere, the overall aim of the KEY-VOCs project is to improve the measurement infrastructure for Key Volatile Organic Compounds in indoor and outdoor air. This is done by providing traceable and comparable reference gas standards and by validating new measurement systems in support to the air monitoring networks.
Design of Reference Materials for Proficiency Tests for Measurements in Emission Test Chambers
(2017)
Emission testing of products is currently a rapidly increasing field of measurement activity. Labelling procedures for construction products are based on such emission test chamber measurements and hence measurement performance should be verified. A suited procedure for this purpose is the testing of one unique homogenous material in different laboratories within a Round Robin Test (RRT). Therefore, it is useful to have a reference material which can be used within inter-laboratory studies or as part of the quality management system to ensure comparable results.
Any commercially available product on the market can be used as reference material, provided it is thoroughly characterised. However, these materials often emit only a few and material specific VOCs and appropriate homogeneity is not given. Therefore, alternative materials should be found.
Several approaches on the development of reproducibly emitting materials have been published. These have in common only to emit a single VOC – toluene. Two further research studies carried out by BAM aimed to develop reference material for emissions testing containing one or more VOC in a single material. The first approach was a doped lacquer with Volatile and Semi-Volatile Organic Compounds (VOC/SVOC) and the second was Thermoplastic Polyurethane (TPU) or a Squalane/Paraffin mixture. Currently, the second approach is not at a level that it could be tested within a RRT.
Important requirements for the production of a reference material were repeatability (homogeneity), reproducibility, long-term stability in terms of compound release and transport stability. The emission rates should be high enough to obtain well measurable chamber air concentrations at standardised test conditions.
The lacquer samples were prepared by weighing portions of a water-based lacquer to which defined amounts of the pure analytes were added. Defined amounts of the lacquer mixture were filled into Petri dishes and cured under standard conditions (23 °C and 50% relative humidity). Reproducible emissions were obtained when the storage time of the cured material was not longer than four weeks. The concentrations were analyzed 7 days after loading of the material into the chamber.
Two RRT were conducted by use of the lacquer system. Here, the laboratories had to identify and also to quantify the compounds. The relative standard deviations obtained were typical for such a kind of test. More than 50 participants reported results.
Since some volatile organic compounds (VOC) are dangerous to human health whilst others cause harm to the environment by influencing the oxidative capacity of the atmosphere, the overall aim of the KEY-VOCs project is to improve the measurement infrastructure for Key Volatile Organic Compounds in indoor and outdoor air. This is done by providing traceable and comparable reference gas standards and by validating new measurement systems in support to the air monitoring networks.
Investigation and control of protein adsorption for fluorescent nanosilver reference material
(2017)
Upon interaction of nanomaterials like noble metal nanoparticles (NPs) with biological systems like body fluids such as serum, a protein corona is formed.[1] This reversibly bound layer of proteins controls the transport of the NPs and their subsequent interaction with biological components.[2] The plasmonic properties of nobel metal NPs like Au and Ag can considerably affect the fluorescence properties of fluorophores in their vicinity, i.e., within a near field distance. Depending on the chemical composition, size and shape of these noble metal NPs, the spectral properties of the dye, and the particle-fluorophore distance, the fluorescence is quenched or in some cases enhanced.[3,4,5] This can be monitored by fluorescence intensity and lifetime measurements, with the latter effect being accompanied by an increase in fluorescence intensity and reduction in fluorescence lifetime due to an increase in radaiative rate constant. We utilized these effects to study and manipulate noble metal NP-protein interaction exemplarily for fluorophore-labeled bovine serum albumin (BSA) modified e.g. by succinylation, amination and the introduction of thiol groups, resulting in different binding affinities of the proteins.[6] Our results show that the fluorescent corona allows monitoring of the interaction of our accordingly protein-functionalized particles with biological model systems like solutions containing different amounts of various proteins. This can be eventually used for further in vitro and in vivo studies to assess the uptake, digestion, and excretion of surface functionalized noble metal NPs.