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Fluorescence techniques are known for their high sensitivity and are widely used as analytical tools and detection methods for product and process control, material sciences, environmental and bio-technical analysis, molecular genetics, cell biology, medical diagnostics, and drug screening. According to DIN/ISO 17025 certified standards are used for fluorescence diagnostics having the drawback of giving relative values for fluorescence intensities only. Therefore reference materials for a quantitative characterization have to be related directly to the materials under investigation. In order to evaluate these figures it is necessary to calculate absolute numbers like absorption/excitation cross sections and quantum yield. This can be done for different types of dopands in different materials like glass, glass ceramics, crystals or nano crystalline material embedded in polymer matrices. Based on the optical spectroscopy data we will discuss options for characteristic doped glasses and glass ceramics with respect to scattering and absorption regime. It has shown recently for YAG:Ce glass ceramics that for a proper determination of the quantum efficiency in these highly scattering media a reference material with similar scattering and fluorescent properties is required. This may be performed using the emission decay measurement diagnostics, where the decay time is below 100 ns. In this paper we present first results of these aspects using well performing LUMOGEN RED organic pigments for a comparison of mainly transparent glass with glass ceramics doped with various amounts of dopands e.g. ions of raw earth elements and transition metals. The LUMOGEN red is embedded in silica and polyurethane matrices. Characterisations on wavelength accuracy and lifetime for different environmental conditions (temperature, UV irradiation) have been performed. Moreover intensity patterns and results for homogeneity, isotropy, photo and thermal stability will be discussed. In a next step we will show the transfer of the characterisation methods to inorganic fluophores (YAG:Ce) in silicon. Fluorescence (steady state, decay time) and absorption (remission, absorption) spectroscopy working in different temperature regimes (10 - 350 K) are employed diagnostic methods in order to get a microscopic view of the relevant physical processes and to prove the correctness of the obtained data. The work is funded by BMBF under project number 13N8849.
Fluorescence techniques are known for their high sensitivity and are widely used as analytical tools and detection methods for product and process control, material sciences, environmental and biotechnical analysis, molecular genetics, cell biology, medical diagnostics, and drug screening. For routine measurements by fluorescence techniques the existence of an improved quality assurance is one of the basic needs. According to DIN/ISO 17025 certified standards are used for fluorescence diagnostics having the drawback of giving relative values only. Typical requirements onto fluorescence reference materials or standards deal with the verification of the instrument performance as well as the improvement of the data comparability. Especially for biomedical applications fluorescence labels are used for the detection of proteins. In particular these labels consist of nano crystalline materials like CdS and CdSe. The field of Non-Cadmium containing materials is under investigation. In order to evaluate whether glass based materials can be used as standards it is necessary to calculate absolute values like absorption/excitation cross sections or relative quantum yields. This can be done using different quantities of dopands in glass, glass ceramics or crystals. The investigated materials are based on different types of glass, silicate, phosphate and boron glass, which play a dominant role for the absorption and emission mechanism. Additional to the so-called elementary fluorescence properties induced by raw earth elements the formation of defects lead to higher cross sections additionally. The main investigations deal with wavelength accuracy and lifetime of doped glasses, glass ceramics and crystalline samples. Moreover intensity patterns, homogeneity aspects and photo stability will be discussed.
Current trends in materials and life sciences are flanked by the need to push detection limits to single molecules or single cells, enable the characterization of increasingly complex matrices or sophisticated nanostructures, speed up the time of analysis, reduce instrument complexity and costs, and improve the reliability of data. This requires suitable analytical tools such as spectroscopic, separation and imaging techniques, mass spectrometry, and hyphenated techniques as well as sensors and their adaptation to application-specific challenges in the environmental, food, consumer product, health sector, nanotechnology, and bioanalysis. Increasing concerns about health threatening known or emerging pollutants in drinking water, consumer products, and food and about the safety of nanomaterials led to a new awareness of the importance of analytical sciences. Another important driver in this direction is the increasing demand by legislation, particularly in view of the 17 sustainable development goals by the United Nations addressing clean energy, industry, and innovation, sustainable cities, clean water, and responsible consumption and production. In this respect, also the development of analytical methods that enable the characterization of material flows in production processes and support recycling concepts of precious raw materials becomes more and more relevant. In the future, this will provide the basis for greener production in the chemical industry utilizing recycled or sustainable starting materials.
This makes analytical chemistry an essential player in terms of the circular economy helping to increase the sustainability of production processes. In the life sciences sector, products based on proteins, such as therapeutic and diagnostic antibodies, increase in importance. These increasingly biotechnologically produced functional biomolecules pose a high level of complexity of matrix and structural features that can be met only by highly advanced methods for separation, characterization, and detection. In addition, metrological traceability and target definition are still significant challenges for the future, particularly in the life sciences.
However, innovative reference materials as required for the health and food sector and the characterization of advanced materials can only be developed when suitable analytical protocols are available. The so-called reproducibility crisis in sciences underlines the importance of improved measures of quality control for all kinds of measurements and material characterization. This calls for thorough method validation concepts, suitable reference materials, and regular interlaboratory comparisons of measurements as well as better training of scientists in analytical sciences.
The important contribution of analytical sciences to these developments is highlighted by a broad collection of research papers, trend articles, and critical reviews from these different application fields. Special emphasis is dedicated to often-overlooked quality assurance and reference materials.
Introduction. Comparing different emitter classes and rationally designing the next generation of molecular and nanoscale probes for bioimaging applications require accurate and quantitative methods for the measurement of the key parameter photoluminescence quantum yield f.1 f equals the number of emitted per number of absorbed photons. This is particularly relevant for increasingly used fluorescence imaging in the short wave-infrared region (SWIR) ≥ 900 nm providing deeper penetration depths, a better image resolution, and an improved signal-to-noise or tumor-to-background ratio.2, 3 However, spectroscopic measurements in the SWIR are more challenging and require specific calibrations and standards.
Fluorescence techniques are known for their high sensitivity and are widely used as analytical tools, detection methods and imaging applications for product and process control, material sciences, environmental and bio-technical analysis, molecular genetics, cell biology, medical diagnostics, and drug screening. According to DIN/ISO 17025 certified standards are used for steady state fluorescence diagnostics, a method having the drawback of giving relative values for fluorescence intensities only. Therefore reference materials for a quantitative characterization have to be related directly to the materials under investigation. In order to evaluate these figures it is necessary to calculate absolute numbers such as absorption/excitation cross sections and quantum yield. This has been done for different types of dopands in different materials such as glass, glass ceramics, crystals or nano crystalline material embedded in polymer matrices. Samples doped with several fluophores of different emission wavelengths and decay times are required for fluorescent multiplexing applications. Decay times shorter than 100 ns are of special interest. In addition, a proper knowledge is necessary of quantum efficiency in highly scattering media. Recently, quantum efficiency in YAG:Ce glass ceramics has been successfully investigated. Glass and glass ceramics doped with threefold charged rare earth elements are available. However, these samples have the disadvantage of emission decay times much longer than 1 microsecond, due to the excitation and emission of their optical forbidden electronic transitions. Therefore first attempts have been made to produce decay-time standards based on organic and inorganic fluophores. Stable LUMOGEN RED pigments and YAG:Ce phosphors are diluted simultaneously in silicone matrices using a wide range of concentrations between 0.0001 and 2 wt%. Organic LUMOGEN RED has decay times in the lower nanosecond range with a slight dependency on concentration and temperature. In addition, the well-known decay properties of inorganic YAG:Ce are observed also embedded in silicone matrix. Luminescent silicone layers are obtained with thicknesses between 150 and 300 m and no change of decay time, which has been determined to be between 60 and 62 ns. Finally, first results are shown for fluorescent CaF2:Pb glass ceramics embedded in a silicate glass matrix. Wavelength accuracy and lifetime are characterized for different environmental conditions such as temperature treatment and UV irradiation. Moreover, intensity patterns, e.g. line profiles and results, are discussed on homogeneity and photo and thermal stability, respectively. Fluorescence (steady state, decay time) and absorption (remission, absorption) spectroscopy are employed as diagnostic methods to get a microscopic view of the relevant physical processes. The work is funded by BMBF under project number 13N8849.
The characterization of the optical properties of photoluminescent systems, that scatter, like dispersions of nanoparticles with sizes exceeding about 25 nm or solid nanophosphors is of increasing importance for many applications in the life and material sciences. Examples present nanoscale optical reporters and dye-doped microparticles for bioimaging, fluorescence assays or DNA sequencing as well as nanocrystalline emitters like semiconductor quantum dots and rods or lanthanide-based nanophosphors embedded into solid matrices for solid state lighting, display technologies, or barcoding/security applications. The assessment and comparison of material performance as well as the development of rational design strategies for improved systems require spectroscopic tools, which enable the determination of the signal-relevant optical properties like photoluminescence quantum yields and brightness values.
This encouraged us to built up an integrating sphere setup enabling absolute measurements of photoluminescence spectra and quantum yields of transparent and scattering photoluminescent dispersions and solid samples in different measurement geometries, i.e., direct and indirect illumination and the combination of both geometries and perform first measurements with selected emitters. Here, the design of this setup is presented and first recommendations concerning suitable measurement geometries are given.
This paper describes the production and characteristics of the nanoparticle test materials prepared for common use in the collaborative research project NanoChOp (Chemical and optical characterization of nanomaterials in biological systems), in casu suspensions of silica nanoparticles and CdSe/CdS/ZnS quantum dots (QDs). This paper is the first to illustrate how to assess whether nanoparticle test materials meet the requirements of a "reference material" (ISO Guide 30, 2015) or rather those of the recently defined category of "representative test material (RTM)" (ISO/TS 16195, 2013). The NanoChOp test materials were investigated with small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), and centrifugal liquid sedimentation (CLS) to establish whether they complied with the required monomodal particle size distribution. The presence of impurities, aggregates, agglomerates, and viable microorganisms in the suspensions was investigated with DLS, CLS, optical and electron microscopy and via plating on nutrient agar. Suitability of surface functionalization was investigated with attenuated total reflection Fourier transform infrared spectrometry (ATR-FTIR) and via the capacity of the nanoparticles to be fluorescently labeled or to bind antibodies. Between-unit homogeneity and stability were investigated in terms of particle size and zeta potential. This paper shows that only based on the outcome of a detailed characterization process one can raise the status of a test material to RTM or reference material, and how this status depends on its intended use.