Ute Resch-genger - Profile on Academia.edu (original) (raw)
Papers by Ute Resch-genger
Spectroscopic properties of upconversion nanoparticles
Lanthanide-doped up-converting nanoparticles (UCNPs) are promising reporters for medical diagnost... more Lanthanide-doped up-converting nanoparticles (UCNPs) are promising reporters for medical diagnostics and bioimaging. Current limitations present their relative low absorption cross sections and low fluorescence efficiencies, with the latter being affected by particle size, surface chemistry, and microenvironment, particularly water. Here, we present results from systematic studies of the excitation power density dependent upconversion luminescence spectra, intensities/intensity ratios of the individual emission bands, slope factors, and quantum yields of UCNPs of varying size, dopant concentration, and surface chemistry in different microenvironments as well as the up- and downconversion luminescence decay kinetics of the different emission bands. Moreover, first studies of the energy transfer from UCNPs to surface-bound organic dyes acting as fluorescence acceptors are shown. Based upon these measurements, fluorescence deactivation channels are identified and spectroscopic parameters for the screening of material performance are derived.
The synthesis of Er3+/Yb3+/K+ triple-doped NaYF4 phosphors and its high sensitivity optical thermometers at low power
Journal of Alloys and Compounds, Mar 1, 2023
Analytical and Bioanalytical Chemistry, Jan 24, 2015
Commercial platforms consisting of ready-to-use microarrays printed with target-specific DNA prob... more Commercial platforms consisting of ready-to-use microarrays printed with target-specific DNA probes, a microarray scanner, and software for data analysis are available for different applications in medical diagnostics and food analysis, detecting, e.g., viral and bacteriological DNA sequences. The transfer of these tools from basic research to routine analysis, their broad acceptance in regulated areas, and their use in medical practice requires suitable calibration tools for regular control of instrument performance in addition to internal assay controls. Here, we present the development of a novel assayadapted calibration slide for a commercialized DNA-based assay platform, consisting of precisely arranged fluorescent areas of various intensities obtained by incorporating different concentrations of a "green" dye and a "red" dye in a polymer matrix. These dyes present "Cy3" and "Cy5" analogues with improved photostability, chosen based upon their spectroscopic properties closely matching those of common labels for the green and red channel of microarray scanners. This simple tool allows to efficiently and regularly assess and control the performance of the microarray scanner provided with the biochip platform and to compare different scanners. It will be eventually used as fluorescence intensity scale for referencing of assays results and to enhance the overall comparability of diagnostic tests.
Sensors and Actuators B-chemical, Nov 1, 2017
A set of highly fluorescent, pH-responsive boron dipyrromethene (BODIPY) dyes covering the pH ran... more A set of highly fluorescent, pH-responsive boron dipyrromethene (BODIPY) dyes covering the pH range of 5 to 12 is presented for broad range pH measurements in mixed aqueous-organic media and polymer matrices. Readout in the intensity domain with low cost and miniaturized instrumentation utilizes reversible protonation induced switching ON of their initially completely quenched fluorescence mediated by photoinduced-electron transfer (PET). All dyes, rationally designed to reveal closely matching absorption and emission properties, are accessible via facile two-step reactions in overall yields of up to 20 %. By modifying the substitution pattern of the mesoaryl substituent, the pK a values could be fine-tuned from 6 to 11. Integration of these molecules into polymeric films by a simple mixing procedure yielded reversible and longterm stable pH sensors for naked eye detection.
ACS Applied Materials & Interfaces, Jun 19, 2018
DNA origami nanostructures provide a platform where dye molecules can be arranged with nanoscale ... more DNA origami nanostructures provide a platform where dye molecules can be arranged with nanoscale accuracy allowing to assemble multiple fluorophores without dye-dye aggregation. Aiming to develop a bright and sensitive ratiometric sensor system, we systematically studied the optical properties of nanoarrays of dyes built on DNA origami platforms using a DNA template that provides a high versatility of label choice at minimum cost. The dyes are arranged at distances, at which they efficiently interact by Forster resonance energy transfer (FRET). To optimize array brightness, the FRET efficiencies between the donor fluorescein (FAM) and the acceptor cyanine 3 were determined for different sizes of the array and for different arrangements of the dye molecules within the array. By utilizing nanoarrays providing optimum FRET efficiency and brightness, we subsequently designed a ratiometric pH nanosensor using coumarin 343 as a pH-inert FRET donor and FAM as a pHresponsive acceptor. Our results indicate that the sensitivity of a ratiometric sensor can be improved simply by arranging the dyes into a well-defined array. The dyes used here can be easily replaced by other analyte-responsive dyes, demonstrating the huge potential of DNA nanotechnology for light harvesting, signal enhancement, and sensing schemes in life sciences.
Nanoscale, Mar 23, 2017
The rational design of brighter upconversion nanoparticles (UCNPs) requires a better understandin... more The rational design of brighter upconversion nanoparticles (UCNPs) requires a better understanding of the radiationless deactivation pathways in these materials. Here, we demonstrate the potential of excitation power density (P)-dependent studies of upconversion (UC) luminescence intensities, slope factors, and absolute quantum yields (Φ UC ) of popular β-NaYF 4 :20% Yb 3+ ,2% Er 3+ UCNPs of different surface chemistries in organic solvents, D 2 O, and water as a tool to gain deeper insight into the UC mechanism including population and deactivation pathways particularly of the red emission. Our measurements, covering a P regime of three orders of magnitude, reveal a strong difference of the P-dependence of the ratio of the green and red luminescence bands (I g/r ) in water and organic solvents and P-dependent population pathways of the different emissive energy levels of Er 3+ . In summary, we provide experimental evidence for three photon processes in UCNPs, particularly for the red emission. Moreover, we demonstrate changes in the excited population dynamics via bi-and triphotonic processes dependent on the environment, surface chemistry, and P, and validate our findings theoretically. † Electronic supplementary information (ESI) available. See
Analytical and Bioanalytical Chemistry, Jul 14, 2017
Lanthanide-doped photon-upconversion nanoparticles (UCNPs) have been the focus of many research a... more Lanthanide-doped photon-upconversion nanoparticles (UCNPs) have been the focus of many research activities in materials and life sciences in the last 15 years because of their potential to convert light between different spectral regions and their unique photophysical properties. To fully exploit the application potential of these fascinating nanomaterials, a number of challenges have to be overcome, such as the low brightness, particularly of small UCNPs, and the reliable quantification of the excitation-power-densitydependent upconversion luminescence. In this series of critical reviews, recent developments in the design, synthesis, optical-spectroscopic characterization, and application of UCNPs are presented with special focus on bioanalysis and the life sciences. Here we guide the reader from the synthesis of UCNPs to different concepts to enhance their luminescence, including the required optical-spectroscopic assessment to quantify material performance; surface modification strategies and bioanalytical applications as well as selected examples of the use of UCNPs as reporters in different assay formats are addressed in part II. Future trends and challenges in the field of upconversion are discussed with special emphasis on UCNP synthesis and material characterization, particularly quantitative luminescence studies.
Chemistry: A European Journal, Aug 13, 2019
Structural modularity of polymer frameworks is a key advantage of covalent organic polymers, howe... more Structural modularity of polymer frameworks is a key advantage of covalent organic polymers, however, only C, N, O, Si, and S have found their way into their building blocks so far. Here, the toolbox available to polymer and materials chemists is expanded by one additional nonmetal, phosphorus. Starting with a building block that contains a l 5 -phosphinine (C 5 P) moiety, a number of polymerization protocols are evaluated, finally obtaining a p-conjugated, covalent phosphinine-based framework (CPF-1) through Suzuki-Miyaura coupling. CPF-1 is a weakly porous polymer glass (72.4 m 2 g À1 BET at 77 K) with green fluorescence (l max = 546 nm) and extremely high thermal stability. The polymer catalyzes hydrogen evolution from water under UV and visible light irradiation without the need for additional co-catalyst at a rate of 33.3 mmol h À1 g À1 . These results demonstrate for the first time the incorporation of the phosphinine motif into a complex polymer framework. Phosphininebased frameworks show promising electronic and optical properties, which might spark future interest in their applications in light-emitting devices and heterogeneous catalysis.
Dalton Transactions, 2013
Analytical and Bioanalytical Chemistry, Mar 22, 2022
For more than 110 years, BAM has been producing reference materials for a wide range of applicati... more For more than 110 years, BAM has been producing reference materials for a wide range of application fields. With the development of new analytical methods and new applications as well as continuously emerging more stringent requirements of laboratory accreditation with regard to quality control and metrological traceability, the demand and requirements for reference materials are increasing. This trend article gives an overview of general developments in the field of reference materials as well as developments in selected fields of application in which BAM is active. This includes inorganic and metal analysis, gas analysis, food and consumer products, and geological samples. In addition to these more traditional fields of application, developments in the areas of optical spectroscopy, particularly fluorescence methods, and nanomaterials are considered.
Журнал технической физики, 2018
Producing active polymer optical fibers (POFs) is a key step towards new applications such as flu... more Producing active polymer optical fibers (POFs) is a key step towards new applications such as fluorescent fiber solar concentrators (FFSCs), sensors, contactless coupling devices, or fiber integrated light sources and lasers. Therefore, integration of fluorescent nanoparticles into the polymer matrix is necessary and becomes accessible via in situ polymerization. For optical applications, the polymer has to fulfill various requirements such as chemical and physical stability, optical transparency in the application-relevant spectral region as well as a good synthetic accessibility. A common material for these is poly(methyl methacrylate) (PMMA). The β-phase NaYF 4 : Yb 3+ , Er 3+ upconversion nanoparticles (UCNP) were synthesized from the rare earth salts via thermal decomposition method in high-boiling point solvent 1-octadecene and capping agent oleic acid. Current results show hazy samples of the polymer with integrated nanoparticles made from monomer solution of methyl methacrylate. However, further optical tuning such as increasing the transparency of the bulk samples by changing the monomer solution to nonpolar n-butyl methacrylate (nButMA) or cyclohexyl methacrylate (CHMA) or further optimization of the UCNP shell could lead to more suitable polymer bulk samples.
Determination of the Critical Micelle Concentration of Neutral and Ionic Surfactants with Fluorometry, Conductometry, and Surface Tension—A Method Comparison
Journal of Fluorescence, 2018
Micelles are of increasing importance as versatile carriers for hydrophobic substances and nanopr... more Micelles are of increasing importance as versatile carriers for hydrophobic substances and nanoprobes for a wide range of pharmaceutical, diagnostic, medical, and therapeutic applications. A key parameter indicating the formation and stability of micelles is the critical micelle concentration (CMC). In this respect, we determined the CMC of common anionic, cationic, and non-ionic surfactants fluorometrically using different fluorescent probes and fluorescence parameters for signal detection and compared the results with conductometric and surface tension measurements. Based upon these results, requirements, advantages, and pitfalls of each method are discussed. Our study underlines the versatility of fluorometric methods that do not impose specific requirements on surfactants and are especially suited for the quantification of very low CMC values. Conductivity and surface tension measurements yield smaller uncertainties particularly for high CMC values, yet are more time- and substance consuming and not suitable for every surfactant.
Simple methods, validation concepts, and reference materials for the characterization of functional nanomaterials and microparticles
The surface chemistry / functionalization of nanomaterials and microparticles largely controls th... more The surface chemistry / functionalization of nanomaterials and microparticles largely controls the stability of these materials as well as their solubility and subsequent biofunctionalization and their interactions with biological systems. Moreover, in the case of some nanomaterials like semiconductor quantum dots or lanthanide-based upconversion nanocrystals, the ligand shell strongly affects their optical properties, e.g., via passivation of surface states and traps that favor luminescence quenching or the protection of surface atoms from quenching water molecules. This renders analytical methods for the quantification of surface groups like functionalities very important. Targets of broad interest are here amino, carboxyl, alkine and maleimide groups used for common bioconjugation reactions and typical ligands like thiols and polyethylene glycol (PEG) molecules of varying length, used for the tuning of material hydrophilicity and biocompatibility, minimization of unspecific interactions, prevention of biofouling, and enhancement of blood circulation times as well as surface-bound biomolecules like streptavidin or other biomolecules relevant e.g., for diagnostic assays. Here, we focus on simple optical methods relying on standard laboratory instrumentation, validated by method comparison and/or mass balances and present examples for their use for the characterization of different types of nanomaterials and microparticles.
![Research paper thumbnail of Corrigendum to “Deep red emitting triphenylamine based coumarin-rhodamine hybrids with large stokes shift and viscosity sensing: Synthesis, photophysical properties and DFT studies of their spirocyclic and open forms” [Dyes Pigments 137 (2017) 329–341]](https://attachments.academia-assets.com/122081882/thumbnails/1.jpg)
](Dyes and Pigments, Feb 1, 2018
Study of the superplasticizer-cement hydration interaction by optical spectroscopy
Chemical admixtures like superplasticizers or stabilizing agents are of ever increasing importanc... more Chemical admixtures like superplasticizers or stabilizing agents are of ever increasing importance for modern concrete technology. Although such admixtures have meanwhile become common practice in many applications of concrete technology, the understanding of these highly complex systems is still limited and the relevant parameters, which predominantly control the interaction between the superplasticizer and the cement components, have not been identified yet. Optical methods have been successfully used for the analysis and monitoring of the interactions between a broad variety of nanoscale and molecular systems like nanoparticles of various chemical composition and different types of organic ligands or biomolecules. This encouraged to assess the potential of these methods for the investigation of the interactions that occur at the interface between particle or hydrate surfaces and the fluid phase at a very early stage of concrete formation and to differentiate between different superplasticizer.
NIR-Emissive Nanosensors for oxygen sensing in tumors
RöFo, Apr 26, 2013
NaYF4:Yb3+/Tm3+@NaYF4:Yb3+ Upconversion Nanoparticles for Optical Temperature Monitoring and Self-Heating in Photothermal Therapy
ACS applied nano materials, Dec 28, 2022
Tailoring of Polymer Surfaces with Monotype Functional Groups of Variable Density Using Chemical and Plasma Chemical Processes
Springer eBooks, Mar 9, 2006
Polymer surfaces were modified in low-pressure glow discharge plasmas for introduction of monotyp... more Polymer surfaces were modified in low-pressure glow discharge plasmas for introduction of monotype functional groups of different type and density. For this purpose three ways are selected, (i) oxygen plasma treatment followed by wet-chemical reduction of O functional groups to OH groups, (ii) plasma bromination for introducing C − Br groups and (iii) coating by deposition of thin plasma (co-) polymerized layers
Frequency-Domain Method for Characterization of Upconversion Luminescence Kinetics
“Green” synthesis of highly luminescent lead-free Cs2AgxNa1−xBiyIn1−yCl6 perovskites
Journal of Materials Chemistry C
Microcrystalline Cs2AgxNa1−xBiyIn1−yCl6 perovskites with tailored composition emitting broadband ... more Microcrystalline Cs2AgxNa1−xBiyIn1−yCl6 perovskites with tailored composition emitting broadband yellow-white photoluminescence with a quantum yield of up to 92% were produced by a new “green” approach under ambient conditions.
Spectroscopic properties of upconversion nanoparticles
Lanthanide-doped up-converting nanoparticles (UCNPs) are promising reporters for medical diagnost... more Lanthanide-doped up-converting nanoparticles (UCNPs) are promising reporters for medical diagnostics and bioimaging. Current limitations present their relative low absorption cross sections and low fluorescence efficiencies, with the latter being affected by particle size, surface chemistry, and microenvironment, particularly water. Here, we present results from systematic studies of the excitation power density dependent upconversion luminescence spectra, intensities/intensity ratios of the individual emission bands, slope factors, and quantum yields of UCNPs of varying size, dopant concentration, and surface chemistry in different microenvironments as well as the up- and downconversion luminescence decay kinetics of the different emission bands. Moreover, first studies of the energy transfer from UCNPs to surface-bound organic dyes acting as fluorescence acceptors are shown. Based upon these measurements, fluorescence deactivation channels are identified and spectroscopic parameters for the screening of material performance are derived.
The synthesis of Er3+/Yb3+/K+ triple-doped NaYF4 phosphors and its high sensitivity optical thermometers at low power
Journal of Alloys and Compounds, Mar 1, 2023
Analytical and Bioanalytical Chemistry, Jan 24, 2015
Commercial platforms consisting of ready-to-use microarrays printed with target-specific DNA prob... more Commercial platforms consisting of ready-to-use microarrays printed with target-specific DNA probes, a microarray scanner, and software for data analysis are available for different applications in medical diagnostics and food analysis, detecting, e.g., viral and bacteriological DNA sequences. The transfer of these tools from basic research to routine analysis, their broad acceptance in regulated areas, and their use in medical practice requires suitable calibration tools for regular control of instrument performance in addition to internal assay controls. Here, we present the development of a novel assayadapted calibration slide for a commercialized DNA-based assay platform, consisting of precisely arranged fluorescent areas of various intensities obtained by incorporating different concentrations of a "green" dye and a "red" dye in a polymer matrix. These dyes present "Cy3" and "Cy5" analogues with improved photostability, chosen based upon their spectroscopic properties closely matching those of common labels for the green and red channel of microarray scanners. This simple tool allows to efficiently and regularly assess and control the performance of the microarray scanner provided with the biochip platform and to compare different scanners. It will be eventually used as fluorescence intensity scale for referencing of assays results and to enhance the overall comparability of diagnostic tests.
Sensors and Actuators B-chemical, Nov 1, 2017
A set of highly fluorescent, pH-responsive boron dipyrromethene (BODIPY) dyes covering the pH ran... more A set of highly fluorescent, pH-responsive boron dipyrromethene (BODIPY) dyes covering the pH range of 5 to 12 is presented for broad range pH measurements in mixed aqueous-organic media and polymer matrices. Readout in the intensity domain with low cost and miniaturized instrumentation utilizes reversible protonation induced switching ON of their initially completely quenched fluorescence mediated by photoinduced-electron transfer (PET). All dyes, rationally designed to reveal closely matching absorption and emission properties, are accessible via facile two-step reactions in overall yields of up to 20 %. By modifying the substitution pattern of the mesoaryl substituent, the pK a values could be fine-tuned from 6 to 11. Integration of these molecules into polymeric films by a simple mixing procedure yielded reversible and longterm stable pH sensors for naked eye detection.
ACS Applied Materials & Interfaces, Jun 19, 2018
DNA origami nanostructures provide a platform where dye molecules can be arranged with nanoscale ... more DNA origami nanostructures provide a platform where dye molecules can be arranged with nanoscale accuracy allowing to assemble multiple fluorophores without dye-dye aggregation. Aiming to develop a bright and sensitive ratiometric sensor system, we systematically studied the optical properties of nanoarrays of dyes built on DNA origami platforms using a DNA template that provides a high versatility of label choice at minimum cost. The dyes are arranged at distances, at which they efficiently interact by Forster resonance energy transfer (FRET). To optimize array brightness, the FRET efficiencies between the donor fluorescein (FAM) and the acceptor cyanine 3 were determined for different sizes of the array and for different arrangements of the dye molecules within the array. By utilizing nanoarrays providing optimum FRET efficiency and brightness, we subsequently designed a ratiometric pH nanosensor using coumarin 343 as a pH-inert FRET donor and FAM as a pHresponsive acceptor. Our results indicate that the sensitivity of a ratiometric sensor can be improved simply by arranging the dyes into a well-defined array. The dyes used here can be easily replaced by other analyte-responsive dyes, demonstrating the huge potential of DNA nanotechnology for light harvesting, signal enhancement, and sensing schemes in life sciences.
Nanoscale, Mar 23, 2017
The rational design of brighter upconversion nanoparticles (UCNPs) requires a better understandin... more The rational design of brighter upconversion nanoparticles (UCNPs) requires a better understanding of the radiationless deactivation pathways in these materials. Here, we demonstrate the potential of excitation power density (P)-dependent studies of upconversion (UC) luminescence intensities, slope factors, and absolute quantum yields (Φ UC ) of popular β-NaYF 4 :20% Yb 3+ ,2% Er 3+ UCNPs of different surface chemistries in organic solvents, D 2 O, and water as a tool to gain deeper insight into the UC mechanism including population and deactivation pathways particularly of the red emission. Our measurements, covering a P regime of three orders of magnitude, reveal a strong difference of the P-dependence of the ratio of the green and red luminescence bands (I g/r ) in water and organic solvents and P-dependent population pathways of the different emissive energy levels of Er 3+ . In summary, we provide experimental evidence for three photon processes in UCNPs, particularly for the red emission. Moreover, we demonstrate changes in the excited population dynamics via bi-and triphotonic processes dependent on the environment, surface chemistry, and P, and validate our findings theoretically. † Electronic supplementary information (ESI) available. See
Analytical and Bioanalytical Chemistry, Jul 14, 2017
Lanthanide-doped photon-upconversion nanoparticles (UCNPs) have been the focus of many research a... more Lanthanide-doped photon-upconversion nanoparticles (UCNPs) have been the focus of many research activities in materials and life sciences in the last 15 years because of their potential to convert light between different spectral regions and their unique photophysical properties. To fully exploit the application potential of these fascinating nanomaterials, a number of challenges have to be overcome, such as the low brightness, particularly of small UCNPs, and the reliable quantification of the excitation-power-densitydependent upconversion luminescence. In this series of critical reviews, recent developments in the design, synthesis, optical-spectroscopic characterization, and application of UCNPs are presented with special focus on bioanalysis and the life sciences. Here we guide the reader from the synthesis of UCNPs to different concepts to enhance their luminescence, including the required optical-spectroscopic assessment to quantify material performance; surface modification strategies and bioanalytical applications as well as selected examples of the use of UCNPs as reporters in different assay formats are addressed in part II. Future trends and challenges in the field of upconversion are discussed with special emphasis on UCNP synthesis and material characterization, particularly quantitative luminescence studies.
Chemistry: A European Journal, Aug 13, 2019
Structural modularity of polymer frameworks is a key advantage of covalent organic polymers, howe... more Structural modularity of polymer frameworks is a key advantage of covalent organic polymers, however, only C, N, O, Si, and S have found their way into their building blocks so far. Here, the toolbox available to polymer and materials chemists is expanded by one additional nonmetal, phosphorus. Starting with a building block that contains a l 5 -phosphinine (C 5 P) moiety, a number of polymerization protocols are evaluated, finally obtaining a p-conjugated, covalent phosphinine-based framework (CPF-1) through Suzuki-Miyaura coupling. CPF-1 is a weakly porous polymer glass (72.4 m 2 g À1 BET at 77 K) with green fluorescence (l max = 546 nm) and extremely high thermal stability. The polymer catalyzes hydrogen evolution from water under UV and visible light irradiation without the need for additional co-catalyst at a rate of 33.3 mmol h À1 g À1 . These results demonstrate for the first time the incorporation of the phosphinine motif into a complex polymer framework. Phosphininebased frameworks show promising electronic and optical properties, which might spark future interest in their applications in light-emitting devices and heterogeneous catalysis.
Dalton Transactions, 2013
Analytical and Bioanalytical Chemistry, Mar 22, 2022
For more than 110 years, BAM has been producing reference materials for a wide range of applicati... more For more than 110 years, BAM has been producing reference materials for a wide range of application fields. With the development of new analytical methods and new applications as well as continuously emerging more stringent requirements of laboratory accreditation with regard to quality control and metrological traceability, the demand and requirements for reference materials are increasing. This trend article gives an overview of general developments in the field of reference materials as well as developments in selected fields of application in which BAM is active. This includes inorganic and metal analysis, gas analysis, food and consumer products, and geological samples. In addition to these more traditional fields of application, developments in the areas of optical spectroscopy, particularly fluorescence methods, and nanomaterials are considered.
Журнал технической физики, 2018
Producing active polymer optical fibers (POFs) is a key step towards new applications such as flu... more Producing active polymer optical fibers (POFs) is a key step towards new applications such as fluorescent fiber solar concentrators (FFSCs), sensors, contactless coupling devices, or fiber integrated light sources and lasers. Therefore, integration of fluorescent nanoparticles into the polymer matrix is necessary and becomes accessible via in situ polymerization. For optical applications, the polymer has to fulfill various requirements such as chemical and physical stability, optical transparency in the application-relevant spectral region as well as a good synthetic accessibility. A common material for these is poly(methyl methacrylate) (PMMA). The β-phase NaYF 4 : Yb 3+ , Er 3+ upconversion nanoparticles (UCNP) were synthesized from the rare earth salts via thermal decomposition method in high-boiling point solvent 1-octadecene and capping agent oleic acid. Current results show hazy samples of the polymer with integrated nanoparticles made from monomer solution of methyl methacrylate. However, further optical tuning such as increasing the transparency of the bulk samples by changing the monomer solution to nonpolar n-butyl methacrylate (nButMA) or cyclohexyl methacrylate (CHMA) or further optimization of the UCNP shell could lead to more suitable polymer bulk samples.
Determination of the Critical Micelle Concentration of Neutral and Ionic Surfactants with Fluorometry, Conductometry, and Surface Tension—A Method Comparison
Journal of Fluorescence, 2018
Micelles are of increasing importance as versatile carriers for hydrophobic substances and nanopr... more Micelles are of increasing importance as versatile carriers for hydrophobic substances and nanoprobes for a wide range of pharmaceutical, diagnostic, medical, and therapeutic applications. A key parameter indicating the formation and stability of micelles is the critical micelle concentration (CMC). In this respect, we determined the CMC of common anionic, cationic, and non-ionic surfactants fluorometrically using different fluorescent probes and fluorescence parameters for signal detection and compared the results with conductometric and surface tension measurements. Based upon these results, requirements, advantages, and pitfalls of each method are discussed. Our study underlines the versatility of fluorometric methods that do not impose specific requirements on surfactants and are especially suited for the quantification of very low CMC values. Conductivity and surface tension measurements yield smaller uncertainties particularly for high CMC values, yet are more time- and substance consuming and not suitable for every surfactant.
Simple methods, validation concepts, and reference materials for the characterization of functional nanomaterials and microparticles
The surface chemistry / functionalization of nanomaterials and microparticles largely controls th... more The surface chemistry / functionalization of nanomaterials and microparticles largely controls the stability of these materials as well as their solubility and subsequent biofunctionalization and their interactions with biological systems. Moreover, in the case of some nanomaterials like semiconductor quantum dots or lanthanide-based upconversion nanocrystals, the ligand shell strongly affects their optical properties, e.g., via passivation of surface states and traps that favor luminescence quenching or the protection of surface atoms from quenching water molecules. This renders analytical methods for the quantification of surface groups like functionalities very important. Targets of broad interest are here amino, carboxyl, alkine and maleimide groups used for common bioconjugation reactions and typical ligands like thiols and polyethylene glycol (PEG) molecules of varying length, used for the tuning of material hydrophilicity and biocompatibility, minimization of unspecific interactions, prevention of biofouling, and enhancement of blood circulation times as well as surface-bound biomolecules like streptavidin or other biomolecules relevant e.g., for diagnostic assays. Here, we focus on simple optical methods relying on standard laboratory instrumentation, validated by method comparison and/or mass balances and present examples for their use for the characterization of different types of nanomaterials and microparticles.
Dyes and Pigments, Feb 1, 2018
Study of the superplasticizer-cement hydration interaction by optical spectroscopy
Chemical admixtures like superplasticizers or stabilizing agents are of ever increasing importanc... more Chemical admixtures like superplasticizers or stabilizing agents are of ever increasing importance for modern concrete technology. Although such admixtures have meanwhile become common practice in many applications of concrete technology, the understanding of these highly complex systems is still limited and the relevant parameters, which predominantly control the interaction between the superplasticizer and the cement components, have not been identified yet. Optical methods have been successfully used for the analysis and monitoring of the interactions between a broad variety of nanoscale and molecular systems like nanoparticles of various chemical composition and different types of organic ligands or biomolecules. This encouraged to assess the potential of these methods for the investigation of the interactions that occur at the interface between particle or hydrate surfaces and the fluid phase at a very early stage of concrete formation and to differentiate between different superplasticizer.
NIR-Emissive Nanosensors for oxygen sensing in tumors
RöFo, Apr 26, 2013
NaYF4:Yb3+/Tm3+@NaYF4:Yb3+ Upconversion Nanoparticles for Optical Temperature Monitoring and Self-Heating in Photothermal Therapy
ACS applied nano materials, Dec 28, 2022
Tailoring of Polymer Surfaces with Monotype Functional Groups of Variable Density Using Chemical and Plasma Chemical Processes
Springer eBooks, Mar 9, 2006
Polymer surfaces were modified in low-pressure glow discharge plasmas for introduction of monotyp... more Polymer surfaces were modified in low-pressure glow discharge plasmas for introduction of monotype functional groups of different type and density. For this purpose three ways are selected, (i) oxygen plasma treatment followed by wet-chemical reduction of O functional groups to OH groups, (ii) plasma bromination for introducing C − Br groups and (iii) coating by deposition of thin plasma (co-) polymerized layers
Frequency-Domain Method for Characterization of Upconversion Luminescence Kinetics
“Green” synthesis of highly luminescent lead-free Cs2AgxNa1−xBiyIn1−yCl6 perovskites
Journal of Materials Chemistry C
Microcrystalline Cs2AgxNa1−xBiyIn1−yCl6 perovskites with tailored composition emitting broadband ... more Microcrystalline Cs2AgxNa1−xBiyIn1−yCl6 perovskites with tailored composition emitting broadband yellow-white photoluminescence with a quantum yield of up to 92% were produced by a new “green” approach under ambient conditions.