Ute Resch-genger - Academia.edu (original) (raw)

Papers by Ute Resch-genger

Proceedings of SPIE, Feb 10, 2011

Indispensable for fluorescence imaging are highly specific and sensitive molecular probes that ab... more Indispensable for fluorescence imaging are highly specific and sensitive molecular probes that absorb and emit in the near infrared (NIR) spectral region and respond to or target molecular species or processes. Here, we present approaches to targeted fluorescent probes for in vivo imaging in the intensity and lifetime domain exploiting NIR dyes. Screening schemes for the fast identification of suitable fluorophores are derived and design criteria for highly emissive optical probes. In addition, as a signal amplification strategy that enables also the use of hydrophobic NIR fluorophores as fluorescent reporters, first steps towards versatile strategies for the preparation of NIR-fluorescent polymeric particles are presented that can be utilized also for the design of targeted and analyte-responsive probes.

Construction and Building Materials, Feb 1, 2021

Abstract Polycarboxylate ethers (PCEs) are widely used in construction, but the exact nature of t... more Abstract Polycarboxylate ethers (PCEs) are widely used in construction, but the exact nature of their interaction with cement is still debated. Aiming at a better understanding of the role of tricalcium aluminate (C3A) in cement hydration, we assessed the potential of optical spectroscopy in combination with a water-soluble fluorescent organic reporter dye (S0586) to monitor the early hydration of C3A in the presence of 26 wt% CaSO4·2H2O (C3A26G-S) with and without PCE. As optical methods, steady-state fluorescence and diffuse reflectance (UV–VisDR) spectroscopy were employed. Phase characterization and particle size distribution were performed with in-situ X-ray diffraction (in-situ XRD) and dynamic light scattering (DLS). Our results show that fluorescence and UV–VisDR spectroscopy can be used to monitor the formation of metastable phases by the disaggregation of the dye S0586 in a cement paste as well as changes in ettringite formation. Addition of PCE slowed down the disaggregation of the dye as reflected by the corresponding changes of the dyes absorption and fluorescence. This prolonged induction period is a well-known side effect of PCEs and agrees with previous reported calorimetric studies and the inhibition of gypsum dissolution observed by in-situ XRD. This demonstrates that fluorescence and UV–VisDR spectroscopy together with a suitable optical probe can provide deeper insights into the influence of PCE on C3A-gypsum hydration which could be e.g., utilized as screening method for comparing the influences of different types of PCEs.

Elsevier eBooks, 2014

Organic fluorescent dyes are a fundamental component in biomedical research and diagnostic imagin... more Organic fluorescent dyes are a fundamental component in biomedical research and diagnostic imaging. The major classes encompass polymethine dyes, xanthene dyes, 4,4′-difluoro-4-bora-3 a ,4 a -diaza- s -indacene (BODIPY) dyes, phenoxazines, and rare earth metal complexes. These compounds have been synthesized in manifold variations to optimize their photophysical properties and physicochemical behavior in physiological media and to enable conjugation to targeting molecules and nanocarriers. Furthermore, stimuli-responsive structural motifs were designed to apply these fluorophores as sensors for disease-related physiological and molecular conditions. This chapter is devoted to the chemical base of optical imaging agents, covering the relevant properties of fluorophores and the synthetic concepts toward intelligent optical imaging probes.

Physical Chemistry Chemical Physics, 2016

The optical properties of semiconductor nanocrystals (SC NCs) are largely controlled by their siz... more The optical properties of semiconductor nanocrystals (SC NCs) are largely controlled by their size and surface chemistry, i.e., the chemical composition and thickness of inorganic passivation shells and the chemical nature and number of surface ligands as well as the strength of their bonds to surface atoms. The latter is particularly important for CdTe NCs, which-together with alloyed Cd x Hg 1Àx Te-are the only SC NCs that can be prepared in water in high quality without the need for an additional inorganic passivation shell. Aiming at a better understanding of the role of stabilizing ligands for the control of the application-relevant fluorescence features of SC NCs, we assessed the influence of two of the most commonly used monodentate thiol ligands, thioglycolic acid (TGA) and mercaptopropionic acid (MPA), on the colloidal stability, photoluminescence (PL) quantum yield (QY), and PL decay behavior of a set of CdTe NC colloids. As an indirect measure for the strength of the coordinative bond of the ligands to SC NC surface atoms, the influence of the pH (pD) and the concentration on the PL properties of these colloids was examined in water and D 2 O and compared to the results from previous dilution studies with a set of thiol-capped Cd 1Àx Hg x Te SC NCs in D 2 O. As a prerequisite for these studies, the number of surface ligands was determined photometrically at different steps of purification after SC NC synthesis with Ellman's test. Our results demonstrate ligand control of the pH-dependent PL of these SC NCs, with MPA-stabilized CdTe NCs being less prone to luminescence quenching than TGA-capped ones. For both types of CdTe colloids, ligand desorption is more pronounced in H 2 O compared to D 2 O, underlining also the role of hydrogen bonding and solvent molecules.

Bioconjugate Chemistry, Jun 26, 2013

The rational design of bright optical probes and dye-biomolecule conjugates in the NIRregion requ... more The rational design of bright optical probes and dye-biomolecule conjugates in the NIRregion requires fluorescent labels that retain their high fluorescence quantum yields when bound to a recognition unit and/or upon interaction with a target. As hydrophilicity-controlled dye aggregation in conjunction with homo-FRET presents one of the major fluorescence deactivation pathways in dye-protein conjugates, fluorescent labels are required that enable higher labeling degrees with minimum dye aggregation. Aiming at a better understanding of the factors governing dye-dye interactions, we systematically studied the signal-relevant spectroscopic properties, hydrophilicity, and aggregation behavior of the novel xS-IDCC series of symmetric pentamethines equipped with 2, 4, and 6 sulfonic acid groups and selected conjugates of these dyes with IgG and the antibody cetuximab (ctx) directed against the Page 1 of 41 ACS Paragon Plus Environment Bioconjugate Chemistry 2 cancer-related epidermal growth factor (EGF) receptor in comparison to the gold standard Cy5.5. With 6S-IDCC that displays a molar absorption coefficient of 190,000 M-1 cm-1 and a fluorescence quantum yield (Φ f) of 0.18 in aqueous media like PBS and nearly no aggregation, we could identify a fluorophore with a similarly good performance as Cy5.5. Bioconjugation of 6S-IDCC and Cy5.5 yielded highly emissive targeted probes with comparable Φ f values of 0.29 for a dye-to-protein (D/P) ratio < 1 and a reduced number of protein-bound dye aggregates in the case of 6S-IDCC. Binding studies of the ctx-conjugates of both dyes performed by fluorescence microscopy and FACS revealed that the binding strength between the targeted probes and the EGF receptor at the cell membrane is independent of D/P ratio. These results underline the importance of an application-specific tuning of dye hydrophilicity for the design of bright fluorescent reporters and efficient optical probes. Moreover, we could demonstrate the potential of fluorescence spectroscopy to predict the size of fluorescence signals resulting for other fluorescence techniques such as FACS. cyanine / cetuximab / IgG / protein labeling / fluorescence quantum yield / hydrophilicity / dimerization constant

Energy and Environmental Science, 2016

We present colloidally stable and highly luminescent Zn x Cd 1Àx S:Mn/ZnS core-shell nanocrystals... more We present colloidally stable and highly luminescent Zn x Cd 1Àx S:Mn/ZnS core-shell nanocrystals (NCs) synthesized via a simple non-injection one-pot, two-step synthetic route, which can be easily upscaled. A systematic variation of the reaction component, parameters and thickness of the ZnS shell yielded doped nanocrystals with a very high photoluminescence quantum yield (F pl) of 70%, which is the highest value yet reported for these Mn-doped sulfide-semiconductor NCs. These materials can be synthesized with high reproducibility in large quantities of the same high quality, i.e., the same F pl using accordingly optimized reaction conditions. The application of these zero-reabsorption high quality NCs in the light conversion layers, deposited on top of a commercial monocrystalline silicon (mono-Si) solar cell, led to a significant enhancement of the external quantum efficiency (EQE) of this device in the ultraviolet spectral region between 300 and 400 nm up to ca. 12%. EQE enhancement is reflected by an increase in the power conversion efficiency (PCE) by nearly 0.5 percentage points and approached the theoretical limit (0.6%) expected from down-shifting for this Si solar cell. The resulting PCE may result in a BoM (bill of materials) cost reduction of app. 3% for mono-Si photovoltaic modules. Such small but distinct improvements are expected to pave the road for an industrial application of doped semiconductor NCs as cost-effective light converters for silicon photovoltaic (PV) and other optoelectronic applications. Broader context The low efficiencies of inorganic solar cells in the ultraviolet (UV) and blue spectral region are key factors which restrict their power conversion efficiency (PCE). A simple and reliable technological step to overcome these limitations, which can be easily introduced into the manufacturing process, is the coating of the cover glass or the solar cells/modules by a light-converting material with high absorption in the UV-blue, luminescence in the active solar cell region, and a high photoluminescence quantum yield/efficiency. The resulting conversion of UV/blue light to the active spectral region of the solar cell can improve PCE by several percentage points, especially in the case of thin-film solar cells based on CuInGaSe 2 or CdTe. Due to the already relatively high efficiency of the monocrystalline silicon (mono-Si) solar cells in the UV (about 45% at 300 nm) the expected improvement of the PCE of these cells is about 0.6 percentage points. Due to the high market share of the mono-Si modules, this improvement is expected to be nevertheless very profitable. To demonstrate the potential of this concept using the most promising type of light converters, that is, zero-reabsorption doped semiconductor quantum dots (QDs), we developed a simple non-injection one-pot, two-step synthetic route towards Zn x Cd 1Àx S:Mn/ZnS core-shell nanocrystals showing a broad and efficient emission centered at 598 nm, which can be easily upscaled, and a simple coating technique to generate down shifting layers applicable to conventional mono-Si solar cells. With this approach, we could improve the efficiency of a commercial Si solar cell by up to ca. 12% in the UV spectral region which led to an enhancement of PCE by nearly 0.5 percentage points and will enable a cost reduction of ca. 3.3%. Our simple strategy is expected to encourage solar module manufacturers to also equip their photovoltaic modules with light converting layers and pave the road to a broader application of solar cells.

Chemical Communications, 2022

The influence of solvent polarity and surface ligand rigidification on the SWIR emission profile ... more The influence of solvent polarity and surface ligand rigidification on the SWIR emission profile of gold nanoclusters with an anistropic surface was investigated. A strong enhancement of the SWIR emission band at 1200 nm was observed when measuring in different local environments: in solution, in polymer composites, and in solids. SWIR in vivo imaging of mice assisted by deep learning after intravenous administration of these gold nanoclusters provides high definition pseudo-3D views of vascular blood vessels.

Chemistry: A European Journal, May 15, 2017

The unparallelede xcited-state potential-energy landscape of the chromium(III)-based dye [1] 3 + ... more The unparallelede xcited-state potential-energy landscape of the chromium(III)-based dye [1] 3 + + ([Cr(ddpd) 2 ] 3 + ;d dpd = N,N'-dimethyl-N,N'-dipyridin-2-ylpyridin-2,6-diamine) enables as trong dual emission in the near infrared region. The temperature dependence of this dual emission allows the use of [1] 3 + + as an unprecedented molecular ratiometric thermometer in the 210-373 Kt emperature range in organic and in aqueous media. Incorporation of [1] 3 + + in biocompatiblen anocarriers, such as 100 nm-sized polystyrene nanoparticles and solutol micelles, providesn anodimensional thermometers operating under physiological conditions.

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

We present here a new approach for non-invasive high resolution whole-body vascular imaging in de... more We present here a new approach for non-invasive high resolution whole-body vascular imaging in depth by combining water-soluble and bright SWIR-emitting gold nanoclusters revealing an anisotropic surface charge with Monte Carlo image processing of the images. We applied and validated this approach to quantify vessel complexity in transgenic mice presenting vascular disorders. In vivo infrared imaging has experienced major breakthroughs over the past few years with potential applications in cancer and cardio-vascular diagnostics1. Hongjie Dai's team was among the first who developed emitters for the shortwave infrared region (SWIR, 900-1700 nm), also called NIR II. Due to the weak photon absorption, the low autofluorescence, and reduced scattering by tissues at these wavelengths compared to NIR I (700-900 nm) and the preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.

Chemical admixtures like superplasticisers or stabilising agents are of ever increasing importanc... more Chemical admixtures like superplasticisers or stabilising agents are of ever increasing importance for modern concrete technology. They liberate the workability of concrete from its dependency on water content, and thus, open the gate towards innovative and future oriented concrete technologies such as selfcompacting concrete. Meanwhile admixtures have become common practice in concrete technology, but the understanding of these highly complex polymers in the entire concrete system lags far behind their application. Due to its complex time-dependent, multi-phase and multi-scale behaviour, flowable concrete systems are highly complicated and cannot be described comprehensively by simple models. It is therefore extremely challenging to identify the relevant parameters that predominantly control flow phenomena on different size scales, since these may occur on any scale between the nano scale (e.g. superplasticizer adsorption) and macro scale (e.g. grading of the aggregates). The prese...

Frontiers in Optics + Laser Science APS/DLS, 2019

We show that Drexhage-type experiment where the silver-coated millimeter-sized sphere is used to ... more We show that Drexhage-type experiment where the silver-coated millimeter-sized sphere is used to measure the local quantum efficiency of pH-dependent fluorescein isothiocyanate bound to a mesoporous silica thin film.

Reducing the size of upconversion nanoparticles (UCNPs) down to a few nm yields unique luminescen... more Reducing the size of upconversion nanoparticles (UCNPs) down to a few nm yields unique luminescent materials containing a very small number of emitters. Considering the bottom limit of one activator per particle, such ultrasmall UCNPs offer an unprecedented platform to study the contributions of the different energy transfer processes at play in upconversion luminescence, especially the role of cross relaxation. Maintaining detectable emission despite the limited number of emitting ions and the high surface-to-volume ratio requires suitable particle architectures. The preparation of Na(Gd-Yb)F4:Tm emissive sub-3 nm diameter ꞵ-phase UCNPs was achieved using a gadolinium-rich composition, in situ mixing of the precursors NaOH and NH4F, and a microwave high-temperature cycling sequence that allowed precise control of the particle size and dispersity. These nanoparticles contain only a single Tm 3+ activator ion, while coating of these cores with a NaGdF4 inert shell was performed to minimize the deleterious influence of surface quenching. The role of cross relaxation in upconversion luminescence was examined by time-resolved luminescence measurements using a combination of standard NIR excitation of the Yb 3+ sensitizer and direct UV excitation of the Tm 3+ activator. The fine tuning of the number of activators per particle via an optimized synthesis pathway along with an appropriate excitation scheme enabled us to select the operating cross relaxation processes and provide an accurate analysis of the different mechanisms at play in these model nanoparticles.

Scientific reports, May 24, 2024

Luminophore stained micro-and nanobeads made from organic polymers like polystyrene (PS) are broa... more Luminophore stained micro-and nanobeads made from organic polymers like polystyrene (PS) are broadly used in the life and material sciences as luminescent reporters, for bead-based assays, sensor arrays, printable barcodes, security inks, and the calibration of fluorescence microscopes and flow cytometers. Initially mostly prepared with organic dyes, meanwhile luminescent core/shell nanoparticles (NPs) like spherical semiconductor quantum dots (QDs) are increasingly employed for bead encoding. This is related to their narrower emission spectra, tuneability of emission color, broad wavelength excitability, and better photostability. However, correlations between particle architecture, morphology, and photoluminescence (PL) of the luminescent nanocrystals used for encoding and the optical properties of the NP-stained beads have been rarely explored. This encouraged us to perform a screening study on the incorporation of different types of luminescent core/shell semiconductor nanocrystals into polymer microparticles (PMPs) by a radical-induced polymerization reaction. Nanocrystals explored include CdSe/CdS QDs of varying CdS shell thickness, a CdSe/ZnS core/shell QD, CdSe/CdS quantum rods (QRs), and CdSe/CdS nanoplatelets (NPLs). Thereby, we focused on the applicability of these NPs for the polymerization synthesis approach used and quantified the preservation of the initial NP luminescence. The spectroscopic characterization of the resulting PMPs revealed the successful staining of the PMPs with luminescent CdSe/CdS QDs and CdSe/CdS NPLs. In contrast, usage of CdSe/CdS QRs and CdSe QDs with a ZnS shell did not yield luminescent PMPs. The results of this study provide new insights into structure-property relationships between NP stained PMPs and the initial luminescent NPs applied for staining and underline the importance of such studies for the performance optimization of NP-stained beads. Luminescent polymer microparticles (PMPs) are frequently utilized in bioanalysis and medical diagnostics 1-4. Typical applications are multimodal and multicolor labels, luminescence sensing of specific targets or biomolecular interactions 5,6 , drug carriers, and calibration beads 5-11. Signal readout is typically performed optically using fluorescence spectroscopy, fluorescence microscopy or flow cytometry 12,13. Combined with magnetic nanoparticles (NPs) like iron oxide NPs, such PMPs are also applied for immunoseparation 14-16. For the preparation of such optically encoded beads, meanwhile different types of luminophores have been employed, including organic dyes, different semiconductor NPs, and lanthanide-based NPs 17-19. Well suited candidates for the luminescence staining of PMPs, e.g., for multiplexing and encoding applications, are photostable quantum dots

Scientific reports, May 24, 2024

Fluorescent labels have strongly contributed to many advancements in bioanalysis, molecular biolo... more Fluorescent labels have strongly contributed to many advancements in bioanalysis, molecular biology, molecular imaging, and medical diagnostics. Despite a large toolbox of molecular and nanoscale fluorophores to choose from, there is still a need for brighter labels, e.g., for flow cytometry and fluorescence microscopy, that are preferably of molecular nature. This requires versatile concepts for fluorophore multimerization, which involves the shielding of dyes from other chromophores and possible quenchers in their neighborhood. In addition, to increase the number of readout parameters for fluorescence microscopy and eventually also flow cytometry, control and tuning of the labels' fluorescence lifetimes is desired. Searching for bright multi-chromophoric or multimeric labels, we developed PEGylated dyes bearing functional groups for their bioconjugation and explored their spectroscopic properties and photostability in comparison to those of the respective monomeric dyes for two exemplarily chosen fluorophores excitable at 488 nm. Subsequently, these dyes were conjugated with anti-CD4 and anti-CD8 immunoglobulins to obtain fluorescent conjugates suitable for the labeling of cells and beads. Finally, the suitability of these novel labels for fluorescence lifetime imaging and target discrimination based upon lifetime measurements was assessed. Based upon the results of our spectroscopic studies including measurements of fluorescence quantum yields (QY) and fluorescence decay kinetics we could demonstrate the absence of significant dye-dye interactions and self-quenching in these multimeric labels. Moreover, in a first fluorescence lifetime imaging (FLIM) study, we could show the future potential of this multimerization concept for lifetime discrimination and multiplexing.

Nanoscale, 2024

Amphiphilic nanogels (ANGs) are promising carriers for hydrophobic cargos such as drugs, dyes, an... more Amphiphilic nanogels (ANGs) are promising carriers for hydrophobic cargos such as drugs, dyes, and catalysts. Loading content and release kinetics of these compounds are controlled by type and number of hydrophobic groups in the amphiphilic copolymer network. Thus, understanding the interactions between cargo and colloidal carrier is mandatory for a tailor-made and cargo-specific ANG design. To systematically explore the influence of the network composition on these interactions, we prepared a set of ANGs of different amphiphilicity and loaded these ANGs with varying concentrations of the solvatochromic dye Nile Red (NR). Here, NR acts as a hydrophobic model cargo to optically probe the polarity of its microenvironment. Analysis of the NR emission spectra as well as measurements of the fluorescence quantum yields and decay kinetics revealed a decrease in the polarity of the NR microenvironment with increasing hydrophobicity of the hydrophobic groups in the ANG network and dye-dye interactions at higher loading concentrations. At low NR concentrations, the hydrophobic cargo NR is encapsulated in the hydrophobic domains. Increasing NR concentrations resulted in probe molecules located in a more hydrophilic environment, i.e., at the nanodomain border, and favored dye-dye interactions and NR aggregation. These results correlate well with release experiments, indicating first NR release from more hydrophilic network locations. Overall, our findings demonstrate the importance to understand carrier-drug interactions for efficient loading and controlled release profiles in amphiphilic nanogels.

Analytical and bioanalytical chemistry/Analytical & bioanalytical chemistry, Mar 13, 2024

The 2023 Nobel Prize in Chemistry was awarded to Aleksey I. Ekimov (prize share 1/3), Louis E. Br... more The 2023 Nobel Prize in Chemistry was awarded to Aleksey I. Ekimov (prize share 1/3), Louis E. Brus (prize share 1/3), and Moungi G. Bawendi (prize share 1/3) for groundbreaking inventions in the field of nanotechnology, i.e., for the discovery and synthesis of semiconductor nanocrystals, also termed quantum dots, that exhibit size-dependent physicochemical properties enabled by quantum size effects. This feature article summarizes the main milestones of the discoveries and developments of quantum dots that paved the road to their versatile applications in solid-state lighting, display technology, energy conversion, medical diagnostics, bioimaging, and image-guided surgery.

Radiology, Jun 1, 2008

To prospectively depict carcinoembryonic antigen (CEA)-expressing tumors in mice with a high-affi... more To prospectively depict carcinoembryonic antigen (CEA)-expressing tumors in mice with a high-affinity probe consisting of a near-infrared (NIR) fluorochrome and the clinically used anti-CEA antibody fragment arcitumomab. This study was approved by the regional animal committee. By coupling a NIR fluorescent (NIRF) cyanine dye (DY-676) to a specific antibody fragment directed against CEA (arcitumomab) and a nonspecific IgG Fab fragment, a bio-optical high-affinity fluorescent probe (anti-CEA-DY-676) and a low-affinity fluorescent probe (FabIgG-DY-676) were designed. The dye-to-protein ratios were determined, and both probes were tested for NIRF imaging in vitro on CEA-expressing LS-174T human colonic adenocarcinoma cells and CEA-nonexpressing A-375 human melanoma cells by using a bio-optical NIR small-animal imager. In vivo data of xenografted LS-174T and A-375 tumors in mice (n = 10) were recorded and statistically analyzed (Student t test). The dye-to-protein ratios were determined as 3.0-3.5 for both probes. In vitro experiments revealed the specific binding of the anti-CEA-DY-676 probe on CEA-expressing cells as compared with CEA-nonexpressing cells; the FabIgG-DY-676 probe showed a markedly lower binding affinity to cells. In vivo LS-174T tumors xenografted in all mice could be significantly distinguished from A-375 tumors with application of the anti-CEA-DY-676 but not with that of the FabIgG-DY-676 at different times (2-24 hours, P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; .005) after intravenous injection of the probes. Semiquantitative analysis revealed maximal fluorescence signals of anti-CEA-DY-676 to CEA-expressing tumors about 8 hours after injection. Findings of this study indicate the potential use of the high-affinity probe anti-CEA-DY-676 for specific NIRF imaging in in vivo tumor diagnosis.

Proceedings of SPIE, Feb 10, 2011

Indispensable for fluorescence imaging are highly specific and sensitive molecular probes that ab... more Indispensable for fluorescence imaging are highly specific and sensitive molecular probes that absorb and emit in the near infrared (NIR) spectral region and respond to or target molecular species or processes. Here, we present approaches to targeted fluorescent probes for in vivo imaging in the intensity and lifetime domain exploiting NIR dyes. Screening schemes for the fast identification of suitable fluorophores are derived and design criteria for highly emissive optical probes. In addition, as a signal amplification strategy that enables also the use of hydrophobic NIR fluorophores as fluorescent reporters, first steps towards versatile strategies for the preparation of NIR-fluorescent polymeric particles are presented that can be utilized also for the design of targeted and analyte-responsive probes.

Construction and Building Materials, Feb 1, 2021

Abstract Polycarboxylate ethers (PCEs) are widely used in construction, but the exact nature of t... more Abstract Polycarboxylate ethers (PCEs) are widely used in construction, but the exact nature of their interaction with cement is still debated. Aiming at a better understanding of the role of tricalcium aluminate (C3A) in cement hydration, we assessed the potential of optical spectroscopy in combination with a water-soluble fluorescent organic reporter dye (S0586) to monitor the early hydration of C3A in the presence of 26 wt% CaSO4·2H2O (C3A26G-S) with and without PCE. As optical methods, steady-state fluorescence and diffuse reflectance (UV–VisDR) spectroscopy were employed. Phase characterization and particle size distribution were performed with in-situ X-ray diffraction (in-situ XRD) and dynamic light scattering (DLS). Our results show that fluorescence and UV–VisDR spectroscopy can be used to monitor the formation of metastable phases by the disaggregation of the dye S0586 in a cement paste as well as changes in ettringite formation. Addition of PCE slowed down the disaggregation of the dye as reflected by the corresponding changes of the dyes absorption and fluorescence. This prolonged induction period is a well-known side effect of PCEs and agrees with previous reported calorimetric studies and the inhibition of gypsum dissolution observed by in-situ XRD. This demonstrates that fluorescence and UV–VisDR spectroscopy together with a suitable optical probe can provide deeper insights into the influence of PCE on C3A-gypsum hydration which could be e.g., utilized as screening method for comparing the influences of different types of PCEs.

Elsevier eBooks, 2014

Organic fluorescent dyes are a fundamental component in biomedical research and diagnostic imagin... more Organic fluorescent dyes are a fundamental component in biomedical research and diagnostic imaging. The major classes encompass polymethine dyes, xanthene dyes, 4,4′-difluoro-4-bora-3 a ,4 a -diaza- s -indacene (BODIPY) dyes, phenoxazines, and rare earth metal complexes. These compounds have been synthesized in manifold variations to optimize their photophysical properties and physicochemical behavior in physiological media and to enable conjugation to targeting molecules and nanocarriers. Furthermore, stimuli-responsive structural motifs were designed to apply these fluorophores as sensors for disease-related physiological and molecular conditions. This chapter is devoted to the chemical base of optical imaging agents, covering the relevant properties of fluorophores and the synthetic concepts toward intelligent optical imaging probes.

Physical Chemistry Chemical Physics, 2016

The optical properties of semiconductor nanocrystals (SC NCs) are largely controlled by their siz... more The optical properties of semiconductor nanocrystals (SC NCs) are largely controlled by their size and surface chemistry, i.e., the chemical composition and thickness of inorganic passivation shells and the chemical nature and number of surface ligands as well as the strength of their bonds to surface atoms. The latter is particularly important for CdTe NCs, which-together with alloyed Cd x Hg 1Àx Te-are the only SC NCs that can be prepared in water in high quality without the need for an additional inorganic passivation shell. Aiming at a better understanding of the role of stabilizing ligands for the control of the application-relevant fluorescence features of SC NCs, we assessed the influence of two of the most commonly used monodentate thiol ligands, thioglycolic acid (TGA) and mercaptopropionic acid (MPA), on the colloidal stability, photoluminescence (PL) quantum yield (QY), and PL decay behavior of a set of CdTe NC colloids. As an indirect measure for the strength of the coordinative bond of the ligands to SC NC surface atoms, the influence of the pH (pD) and the concentration on the PL properties of these colloids was examined in water and D 2 O and compared to the results from previous dilution studies with a set of thiol-capped Cd 1Àx Hg x Te SC NCs in D 2 O. As a prerequisite for these studies, the number of surface ligands was determined photometrically at different steps of purification after SC NC synthesis with Ellman's test. Our results demonstrate ligand control of the pH-dependent PL of these SC NCs, with MPA-stabilized CdTe NCs being less prone to luminescence quenching than TGA-capped ones. For both types of CdTe colloids, ligand desorption is more pronounced in H 2 O compared to D 2 O, underlining also the role of hydrogen bonding and solvent molecules.

Bioconjugate Chemistry, Jun 26, 2013

The rational design of bright optical probes and dye-biomolecule conjugates in the NIRregion requ... more The rational design of bright optical probes and dye-biomolecule conjugates in the NIRregion requires fluorescent labels that retain their high fluorescence quantum yields when bound to a recognition unit and/or upon interaction with a target. As hydrophilicity-controlled dye aggregation in conjunction with homo-FRET presents one of the major fluorescence deactivation pathways in dye-protein conjugates, fluorescent labels are required that enable higher labeling degrees with minimum dye aggregation. Aiming at a better understanding of the factors governing dye-dye interactions, we systematically studied the signal-relevant spectroscopic properties, hydrophilicity, and aggregation behavior of the novel xS-IDCC series of symmetric pentamethines equipped with 2, 4, and 6 sulfonic acid groups and selected conjugates of these dyes with IgG and the antibody cetuximab (ctx) directed against the Page 1 of 41 ACS Paragon Plus Environment Bioconjugate Chemistry 2 cancer-related epidermal growth factor (EGF) receptor in comparison to the gold standard Cy5.5. With 6S-IDCC that displays a molar absorption coefficient of 190,000 M-1 cm-1 and a fluorescence quantum yield (Φ f) of 0.18 in aqueous media like PBS and nearly no aggregation, we could identify a fluorophore with a similarly good performance as Cy5.5. Bioconjugation of 6S-IDCC and Cy5.5 yielded highly emissive targeted probes with comparable Φ f values of 0.29 for a dye-to-protein (D/P) ratio < 1 and a reduced number of protein-bound dye aggregates in the case of 6S-IDCC. Binding studies of the ctx-conjugates of both dyes performed by fluorescence microscopy and FACS revealed that the binding strength between the targeted probes and the EGF receptor at the cell membrane is independent of D/P ratio. These results underline the importance of an application-specific tuning of dye hydrophilicity for the design of bright fluorescent reporters and efficient optical probes. Moreover, we could demonstrate the potential of fluorescence spectroscopy to predict the size of fluorescence signals resulting for other fluorescence techniques such as FACS. cyanine / cetuximab / IgG / protein labeling / fluorescence quantum yield / hydrophilicity / dimerization constant

Energy and Environmental Science, 2016

We present colloidally stable and highly luminescent Zn x Cd 1Àx S:Mn/ZnS core-shell nanocrystals... more We present colloidally stable and highly luminescent Zn x Cd 1Àx S:Mn/ZnS core-shell nanocrystals (NCs) synthesized via a simple non-injection one-pot, two-step synthetic route, which can be easily upscaled. A systematic variation of the reaction component, parameters and thickness of the ZnS shell yielded doped nanocrystals with a very high photoluminescence quantum yield (F pl) of 70%, which is the highest value yet reported for these Mn-doped sulfide-semiconductor NCs. These materials can be synthesized with high reproducibility in large quantities of the same high quality, i.e., the same F pl using accordingly optimized reaction conditions. The application of these zero-reabsorption high quality NCs in the light conversion layers, deposited on top of a commercial monocrystalline silicon (mono-Si) solar cell, led to a significant enhancement of the external quantum efficiency (EQE) of this device in the ultraviolet spectral region between 300 and 400 nm up to ca. 12%. EQE enhancement is reflected by an increase in the power conversion efficiency (PCE) by nearly 0.5 percentage points and approached the theoretical limit (0.6%) expected from down-shifting for this Si solar cell. The resulting PCE may result in a BoM (bill of materials) cost reduction of app. 3% for mono-Si photovoltaic modules. Such small but distinct improvements are expected to pave the road for an industrial application of doped semiconductor NCs as cost-effective light converters for silicon photovoltaic (PV) and other optoelectronic applications. Broader context The low efficiencies of inorganic solar cells in the ultraviolet (UV) and blue spectral region are key factors which restrict their power conversion efficiency (PCE). A simple and reliable technological step to overcome these limitations, which can be easily introduced into the manufacturing process, is the coating of the cover glass or the solar cells/modules by a light-converting material with high absorption in the UV-blue, luminescence in the active solar cell region, and a high photoluminescence quantum yield/efficiency. The resulting conversion of UV/blue light to the active spectral region of the solar cell can improve PCE by several percentage points, especially in the case of thin-film solar cells based on CuInGaSe 2 or CdTe. Due to the already relatively high efficiency of the monocrystalline silicon (mono-Si) solar cells in the UV (about 45% at 300 nm) the expected improvement of the PCE of these cells is about 0.6 percentage points. Due to the high market share of the mono-Si modules, this improvement is expected to be nevertheless very profitable. To demonstrate the potential of this concept using the most promising type of light converters, that is, zero-reabsorption doped semiconductor quantum dots (QDs), we developed a simple non-injection one-pot, two-step synthetic route towards Zn x Cd 1Àx S:Mn/ZnS core-shell nanocrystals showing a broad and efficient emission centered at 598 nm, which can be easily upscaled, and a simple coating technique to generate down shifting layers applicable to conventional mono-Si solar cells. With this approach, we could improve the efficiency of a commercial Si solar cell by up to ca. 12% in the UV spectral region which led to an enhancement of PCE by nearly 0.5 percentage points and will enable a cost reduction of ca. 3.3%. Our simple strategy is expected to encourage solar module manufacturers to also equip their photovoltaic modules with light converting layers and pave the road to a broader application of solar cells.

Chemical Communications, 2022

The influence of solvent polarity and surface ligand rigidification on the SWIR emission profile ... more The influence of solvent polarity and surface ligand rigidification on the SWIR emission profile of gold nanoclusters with an anistropic surface was investigated. A strong enhancement of the SWIR emission band at 1200 nm was observed when measuring in different local environments: in solution, in polymer composites, and in solids. SWIR in vivo imaging of mice assisted by deep learning after intravenous administration of these gold nanoclusters provides high definition pseudo-3D views of vascular blood vessels.

Chemistry: A European Journal, May 15, 2017

The unparallelede xcited-state potential-energy landscape of the chromium(III)-based dye [1] 3 + ... more The unparallelede xcited-state potential-energy landscape of the chromium(III)-based dye [1] 3 + + ([Cr(ddpd) 2 ] 3 + ;d dpd = N,N'-dimethyl-N,N'-dipyridin-2-ylpyridin-2,6-diamine) enables as trong dual emission in the near infrared region. The temperature dependence of this dual emission allows the use of [1] 3 + + as an unprecedented molecular ratiometric thermometer in the 210-373 Kt emperature range in organic and in aqueous media. Incorporation of [1] 3 + + in biocompatiblen anocarriers, such as 100 nm-sized polystyrene nanoparticles and solutol micelles, providesn anodimensional thermometers operating under physiological conditions.

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

We present here a new approach for non-invasive high resolution whole-body vascular imaging in de... more We present here a new approach for non-invasive high resolution whole-body vascular imaging in depth by combining water-soluble and bright SWIR-emitting gold nanoclusters revealing an anisotropic surface charge with Monte Carlo image processing of the images. We applied and validated this approach to quantify vessel complexity in transgenic mice presenting vascular disorders. In vivo infrared imaging has experienced major breakthroughs over the past few years with potential applications in cancer and cardio-vascular diagnostics1. Hongjie Dai's team was among the first who developed emitters for the shortwave infrared region (SWIR, 900-1700 nm), also called NIR II. Due to the weak photon absorption, the low autofluorescence, and reduced scattering by tissues at these wavelengths compared to NIR I (700-900 nm) and the preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.

Chemical admixtures like superplasticisers or stabilising agents are of ever increasing importanc... more Chemical admixtures like superplasticisers or stabilising agents are of ever increasing importance for modern concrete technology. They liberate the workability of concrete from its dependency on water content, and thus, open the gate towards innovative and future oriented concrete technologies such as selfcompacting concrete. Meanwhile admixtures have become common practice in concrete technology, but the understanding of these highly complex polymers in the entire concrete system lags far behind their application. Due to its complex time-dependent, multi-phase and multi-scale behaviour, flowable concrete systems are highly complicated and cannot be described comprehensively by simple models. It is therefore extremely challenging to identify the relevant parameters that predominantly control flow phenomena on different size scales, since these may occur on any scale between the nano scale (e.g. superplasticizer adsorption) and macro scale (e.g. grading of the aggregates). The prese...

Frontiers in Optics + Laser Science APS/DLS, 2019

We show that Drexhage-type experiment where the silver-coated millimeter-sized sphere is used to ... more We show that Drexhage-type experiment where the silver-coated millimeter-sized sphere is used to measure the local quantum efficiency of pH-dependent fluorescein isothiocyanate bound to a mesoporous silica thin film.

Reducing the size of upconversion nanoparticles (UCNPs) down to a few nm yields unique luminescen... more Reducing the size of upconversion nanoparticles (UCNPs) down to a few nm yields unique luminescent materials containing a very small number of emitters. Considering the bottom limit of one activator per particle, such ultrasmall UCNPs offer an unprecedented platform to study the contributions of the different energy transfer processes at play in upconversion luminescence, especially the role of cross relaxation. Maintaining detectable emission despite the limited number of emitting ions and the high surface-to-volume ratio requires suitable particle architectures. The preparation of Na(Gd-Yb)F4:Tm emissive sub-3 nm diameter ꞵ-phase UCNPs was achieved using a gadolinium-rich composition, in situ mixing of the precursors NaOH and NH4F, and a microwave high-temperature cycling sequence that allowed precise control of the particle size and dispersity. These nanoparticles contain only a single Tm 3+ activator ion, while coating of these cores with a NaGdF4 inert shell was performed to minimize the deleterious influence of surface quenching. The role of cross relaxation in upconversion luminescence was examined by time-resolved luminescence measurements using a combination of standard NIR excitation of the Yb 3+ sensitizer and direct UV excitation of the Tm 3+ activator. The fine tuning of the number of activators per particle via an optimized synthesis pathway along with an appropriate excitation scheme enabled us to select the operating cross relaxation processes and provide an accurate analysis of the different mechanisms at play in these model nanoparticles.

Scientific reports, May 24, 2024

Luminophore stained micro-and nanobeads made from organic polymers like polystyrene (PS) are broa... more Luminophore stained micro-and nanobeads made from organic polymers like polystyrene (PS) are broadly used in the life and material sciences as luminescent reporters, for bead-based assays, sensor arrays, printable barcodes, security inks, and the calibration of fluorescence microscopes and flow cytometers. Initially mostly prepared with organic dyes, meanwhile luminescent core/shell nanoparticles (NPs) like spherical semiconductor quantum dots (QDs) are increasingly employed for bead encoding. This is related to their narrower emission spectra, tuneability of emission color, broad wavelength excitability, and better photostability. However, correlations between particle architecture, morphology, and photoluminescence (PL) of the luminescent nanocrystals used for encoding and the optical properties of the NP-stained beads have been rarely explored. This encouraged us to perform a screening study on the incorporation of different types of luminescent core/shell semiconductor nanocrystals into polymer microparticles (PMPs) by a radical-induced polymerization reaction. Nanocrystals explored include CdSe/CdS QDs of varying CdS shell thickness, a CdSe/ZnS core/shell QD, CdSe/CdS quantum rods (QRs), and CdSe/CdS nanoplatelets (NPLs). Thereby, we focused on the applicability of these NPs for the polymerization synthesis approach used and quantified the preservation of the initial NP luminescence. The spectroscopic characterization of the resulting PMPs revealed the successful staining of the PMPs with luminescent CdSe/CdS QDs and CdSe/CdS NPLs. In contrast, usage of CdSe/CdS QRs and CdSe QDs with a ZnS shell did not yield luminescent PMPs. The results of this study provide new insights into structure-property relationships between NP stained PMPs and the initial luminescent NPs applied for staining and underline the importance of such studies for the performance optimization of NP-stained beads. Luminescent polymer microparticles (PMPs) are frequently utilized in bioanalysis and medical diagnostics 1-4. Typical applications are multimodal and multicolor labels, luminescence sensing of specific targets or biomolecular interactions 5,6 , drug carriers, and calibration beads 5-11. Signal readout is typically performed optically using fluorescence spectroscopy, fluorescence microscopy or flow cytometry 12,13. Combined with magnetic nanoparticles (NPs) like iron oxide NPs, such PMPs are also applied for immunoseparation 14-16. For the preparation of such optically encoded beads, meanwhile different types of luminophores have been employed, including organic dyes, different semiconductor NPs, and lanthanide-based NPs 17-19. Well suited candidates for the luminescence staining of PMPs, e.g., for multiplexing and encoding applications, are photostable quantum dots

Scientific reports, May 24, 2024

Fluorescent labels have strongly contributed to many advancements in bioanalysis, molecular biolo... more Fluorescent labels have strongly contributed to many advancements in bioanalysis, molecular biology, molecular imaging, and medical diagnostics. Despite a large toolbox of molecular and nanoscale fluorophores to choose from, there is still a need for brighter labels, e.g., for flow cytometry and fluorescence microscopy, that are preferably of molecular nature. This requires versatile concepts for fluorophore multimerization, which involves the shielding of dyes from other chromophores and possible quenchers in their neighborhood. In addition, to increase the number of readout parameters for fluorescence microscopy and eventually also flow cytometry, control and tuning of the labels' fluorescence lifetimes is desired. Searching for bright multi-chromophoric or multimeric labels, we developed PEGylated dyes bearing functional groups for their bioconjugation and explored their spectroscopic properties and photostability in comparison to those of the respective monomeric dyes for two exemplarily chosen fluorophores excitable at 488 nm. Subsequently, these dyes were conjugated with anti-CD4 and anti-CD8 immunoglobulins to obtain fluorescent conjugates suitable for the labeling of cells and beads. Finally, the suitability of these novel labels for fluorescence lifetime imaging and target discrimination based upon lifetime measurements was assessed. Based upon the results of our spectroscopic studies including measurements of fluorescence quantum yields (QY) and fluorescence decay kinetics we could demonstrate the absence of significant dye-dye interactions and self-quenching in these multimeric labels. Moreover, in a first fluorescence lifetime imaging (FLIM) study, we could show the future potential of this multimerization concept for lifetime discrimination and multiplexing.

Nanoscale, 2024

Amphiphilic nanogels (ANGs) are promising carriers for hydrophobic cargos such as drugs, dyes, an... more Amphiphilic nanogels (ANGs) are promising carriers for hydrophobic cargos such as drugs, dyes, and catalysts. Loading content and release kinetics of these compounds are controlled by type and number of hydrophobic groups in the amphiphilic copolymer network. Thus, understanding the interactions between cargo and colloidal carrier is mandatory for a tailor-made and cargo-specific ANG design. To systematically explore the influence of the network composition on these interactions, we prepared a set of ANGs of different amphiphilicity and loaded these ANGs with varying concentrations of the solvatochromic dye Nile Red (NR). Here, NR acts as a hydrophobic model cargo to optically probe the polarity of its microenvironment. Analysis of the NR emission spectra as well as measurements of the fluorescence quantum yields and decay kinetics revealed a decrease in the polarity of the NR microenvironment with increasing hydrophobicity of the hydrophobic groups in the ANG network and dye-dye interactions at higher loading concentrations. At low NR concentrations, the hydrophobic cargo NR is encapsulated in the hydrophobic domains. Increasing NR concentrations resulted in probe molecules located in a more hydrophilic environment, i.e., at the nanodomain border, and favored dye-dye interactions and NR aggregation. These results correlate well with release experiments, indicating first NR release from more hydrophilic network locations. Overall, our findings demonstrate the importance to understand carrier-drug interactions for efficient loading and controlled release profiles in amphiphilic nanogels.

Analytical and bioanalytical chemistry/Analytical & bioanalytical chemistry, Mar 13, 2024

The 2023 Nobel Prize in Chemistry was awarded to Aleksey I. Ekimov (prize share 1/3), Louis E. Br... more The 2023 Nobel Prize in Chemistry was awarded to Aleksey I. Ekimov (prize share 1/3), Louis E. Brus (prize share 1/3), and Moungi G. Bawendi (prize share 1/3) for groundbreaking inventions in the field of nanotechnology, i.e., for the discovery and synthesis of semiconductor nanocrystals, also termed quantum dots, that exhibit size-dependent physicochemical properties enabled by quantum size effects. This feature article summarizes the main milestones of the discoveries and developments of quantum dots that paved the road to their versatile applications in solid-state lighting, display technology, energy conversion, medical diagnostics, bioimaging, and image-guided surgery.

Radiology, Jun 1, 2008

To prospectively depict carcinoembryonic antigen (CEA)-expressing tumors in mice with a high-affi... more To prospectively depict carcinoembryonic antigen (CEA)-expressing tumors in mice with a high-affinity probe consisting of a near-infrared (NIR) fluorochrome and the clinically used anti-CEA antibody fragment arcitumomab. This study was approved by the regional animal committee. By coupling a NIR fluorescent (NIRF) cyanine dye (DY-676) to a specific antibody fragment directed against CEA (arcitumomab) and a nonspecific IgG Fab fragment, a bio-optical high-affinity fluorescent probe (anti-CEA-DY-676) and a low-affinity fluorescent probe (FabIgG-DY-676) were designed. The dye-to-protein ratios were determined, and both probes were tested for NIRF imaging in vitro on CEA-expressing LS-174T human colonic adenocarcinoma cells and CEA-nonexpressing A-375 human melanoma cells by using a bio-optical NIR small-animal imager. In vivo data of xenografted LS-174T and A-375 tumors in mice (n = 10) were recorded and statistically analyzed (Student t test). The dye-to-protein ratios were determined as 3.0-3.5 for both probes. In vitro experiments revealed the specific binding of the anti-CEA-DY-676 probe on CEA-expressing cells as compared with CEA-nonexpressing cells; the FabIgG-DY-676 probe showed a markedly lower binding affinity to cells. In vivo LS-174T tumors xenografted in all mice could be significantly distinguished from A-375 tumors with application of the anti-CEA-DY-676 but not with that of the FabIgG-DY-676 at different times (2-24 hours, P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; .005) after intravenous injection of the probes. Semiquantitative analysis revealed maximal fluorescence signals of anti-CEA-DY-676 to CEA-expressing tumors about 8 hours after injection. Findings of this study indicate the potential use of the high-affinity probe anti-CEA-DY-676 for specific NIRF imaging in in vivo tumor diagnosis.