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By varying reaction parameters for the syntheses of the hydrogen-bonded metal-imidazolate frameworks (HIF) HIF-1 and HIF-2 (featuring 14 Zn and 14 Co atoms, respectively) to increase their yields and crystallinity, we found that HIF-1 is generated in two different frameworks, named as HIF-1a and HIF-1b. HIF-1b is isostructural to HIF-2. We determined the gas sorption and magnetic properties of HIF-2. In comparison to HIF-1a (Brunauer-Emmett-Teller (BET) surface area of 471m(2) g(-1)), HIF-2 possesses overall very low gas sorption uptake capacities [BET(CO2) surface area=85m(2) g(-1)]. Variable temperature magnetic susceptibility measurement of HIF-2 showed antiferromagnetic exchange interactions between the cobalt(II) high-spin centres at lower temperature. Theoretical analysis by density functional theory confirmed this finding. The UV/Vis-reflection spectra of HIF-1 (mixture of HIF-1a and b), HIF-2 and HIF-3 (with 14 Cd atoms) were measured and showed a characteristic absorption band centered at 340nm, which was indicative for differences in the imidazolate framework.
The formation of secondary Ln(III) solid phases (e.g. Nd(OH)CO3 and Sm(OH)CO3) has been studied as a function of the humic acid (HA) concentration in 0.1 M NaClO4 aqueous solution and their solubility has been investigated in the neutral pH range (6.5-8) under normal atmospheric conditions. Nd(III) and Sm(III) were selected as analogues for trivalent lanthanide and actinide ions. The solid phases under investigation have been prepared by alkaline precipitation and characterized by TGA, ATR-FTIR, XRD, TRLFS, DR-UV-Vis and Raman spectroscopy, and solubility measurements. The spectroscopic data obtained indicate that Nd(OH)CO3 and Sm(OH)CO3 are stable and remain the solubility limiting solid phases even in the presence of increased HA concentration (0.5 g/L) in solution. Upon base addition in the Ln(III)-HA system decomplexation of the previously formed Ln(III)-humate complexes and precipitation of two distinct phases occurs, the inorganic (Ln(OH)CO3) and the organic phase (HA), which is adsorbed on the particle surface of the former. Nevertheless, HA affects the particle size of the solid phases. Increasing HA concentration results in decreasing crystallite size of the Nd(OH)CO3 and increasing crystallite size of the Sm(OH)CO3 solid phase, and affects inversely the solubility of the solid phases. However, this impact on the solid phase properties is expected to be of minor relevance regarding the chemical behavior and migration of trivalent lanthanides and actinides in the geosphere.
The formation of secondary Ln(III) solid phases (e.g., Nd-2(CO3)(3) and Sm-2(CO3)(3)) was studied as a function of the humic acid concentration in 0.1 mol/L NaClO4 aqueous solution in the neutral pH range (5-6.5). The solid phases under investigation were prepared by alkaline precipitation under 100% CO2 atmosphere and characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), time-resolved laser fluorescence spectroscopy (TRLFS), diffuse reflectance ultraviolet-visible (DR-UV-Vis), Raman spectroscopy, and solubility measurements. The spectroscopic data obtained indicated that Nd-2(CO3)(3) and Sm-2(CO3)(3) were stable and remained the solubility limiting solid phases even in the presence of increased humic acid concentration (0.5 g/L) in solution. Upon base addition in the Ln(III)-HA system, decomplexation of the previously formed Ln(III)-humate complexes and precipitation of two distinct phases occurred, the inorganic (Ln(2)(CO3)(3)) and the organic phase (HA), which was adsorbed on the particle surface of the former. Nevertheless, humic acid affected the particle size of the solid phases. Increasing humic acid concentration resulted in decreasing crystallite size of the Nd-2(CO3)(3) and increasing crystallite size of the Sm-2(CO3)(3) solid phase, and affected inversely the solubility of the solid phases. However, this impact on the solid phase properties was expected to be of minor relevance regarding the chemical behavior and migration of trivalent lanthanides and actinides in the geosphere.
Lanthanide resonance energy transfer (LRET) was used to investigate the motion of dopant ions during the synthesis of core-shell-shell-nanocrystals (NCs) that are frequently used as frequency upconversion materials. Reaction conditions (temperature, solvent) as well as lattice composition and precursors were adapted from a typical hydrothermal synthesis approach used to obtain upconversion nanoparticles (UCNPs). Instead of adding the lanthanide ions Yb3+/Er3+ as the sensitizer/activator couple, Eu3+/Nd3+ as the donor/acceptor were added as the LRET pair to the outer shell (Eu-3) and the core (Nd-3). By tailoring the thickness of the insulation shell ("middle shell"), the expected distance between the donor and the acceptor was increased beyond 2 R-0, a distance for which no LRET is expected. The successful synthesis of core- shell-shell NCs with different thicknesses of the insulation layer was demonstrated by high-resolution transmission electron microscopy measurement. The incorporation of the Eu3+ ions into the NaYF4 lattice was investigated by high-resolution time-resolved luminescence measurements. Two major Eu3+ species (bulk and surface) were found. This was supported by steady-state as well as time-resolved luminescence data. Based on the luminescence decay kinetics, the intermixing of lanthanides during synthesis of core- shell UCNPs was evaluated. The energy transfer between Eu3+ (donor) and Nd3+ (acceptor) ions was exploited to quantify the motion of the dopant ions. This investigation reveals the migration of Ln(3+) ions between different compatiments in core-shell NCs and affects the concept of using core-shell architectures to increase the efficiency of UCNPs. In order to obtain well-separated core and shell structures with different dopants, alternative concepts are needed.
The imagination of clearly separated core-shell structures is already outdated by the fact, that the nanoparticle core-shell structures remain in terms of efficiency behind their respective bulk material due to intermixing between core and shell dopant ions. In order to optimize the photoluminescence of core-shell UCNP the intermixing should be as small as possible and therefore, key parameters of this process need to be identified. In the present work the Ln(III) ion migration in the host lattices NaYF4 and NaGdF4 was monitored. These investigations have been performed by laser spectroscopy with help of lanthanide resonance energy transfer (LRET) between Eu(III) as donor and Pr(III) or Nd(III) as acceptor. The LRET is evaluated based on the Forster theory. The findings corroborate the literature and point out the migration of ions in the host lattices. Based on the introduced LRET model, the acceptor concentration in the surrounding of one donor depends clearly on the design of the applied core-shell-shell nanoparticles. In general, thinner intermediate insulating shells lead to higher acceptor concentration, stronger quenching of the Eu(III) donor and subsequently stronger sensitization of the Pr(III) or the Nd(III) acceptors. The choice of the host lattice as well as of the synthesis temperature are parameters to be considered for the intermixing process.
Bioinspired confinement of upconversion nanoparticles for improved performance in aqueous solution
(2020)
The resonance energy transfer (RET) from NaYF4:Yb,Er upconverting nanoparticles (UNCPs) to a dye (5-carboxytetramethylrhodamine (TAMRA)) was investigated by photoluminescence experiments and microscale thermophoresis (MST). The dye was excited via RET from the UCNPs which was excited in the near-infrared (NIR). The change of the dye diffusion speed (free vs coupled) was investigated by MST. RET shows significant changes in the decay times of the dye as well as of the UCNPs. MST reveals significant changes in the diffusion speed. A unique amphiphilic coating polymer (customized mussel protein (CMP) polymer) for UCNP surface coating was used, which mimics blood protein adsorption and mussel food protein adhesion to transfer the UCNP into the aqueous phase and to allow surface functionalization. The CMP provides very good water dispersibility to the UCNPs and minimizes ligand exchange and subsequent UCNP aging reactions because of the interlinkage of the CMP on the UCNP surface. Moreover, CMP provides N-3-functional groups for dick chemistry-based functionalization demonstrated with the dye 5-carboxytetramethylrhodamine (TAMRA). This establishes the principle coupling scheme for suitable biomarkers such as antibodies. The CMP provides very stable aqueous UCNP dispersions that are storable up to 3 years in a fridge at 5 degrees C without dissolution or coagulation. The outstanding properties of CMP in shielding the UCNP from unwanted solvent effects is reflected in the distinct increase of the photoluminescence decay times after UCNP functionalization. The UCNP-to-TAMRA energy transfer is also spectroscopically investigated at low temperatures (4-200 K), revealing that one of the two green Er(III) emission bands contributes the major part to the energy transfer. The TAMRA fluorescence decay time increases by a factor of 9500 from 2.28 ns up to 22 mu s due to radiationless energy transfer from the UCNP after NIR excitation of the latter. This underlines the unique properties of CMP as a versatile capping ligand for distinctly improving the UCNPs' performance in aqueous solutions, for coupling of biomolecules, and for applications for in vitro and in vivo experiments using UCNPs as optical probes in life science applications.
Results of an inter-laboratory round-robin study of the application of time-resolved emission spectroscopy (TRES) to the speciation of uranium(VI) in aqueous media are presented. The round-robin study involved 13 independent laboratories, using various instrumentation and data analysis methods. Samples were prepared based on appropriate speciation diagrams and, in general, were found to be chemically stable for at least six months. Four different types of aqueous uranyl solutions were studied: (1) acidic medium where UO22+aq is the single emitting species, (2) uranyl in the presence of fluoride ions, (3) uranyl in the presence of sulfate ions, and (4) uranyl in aqueous solutions at different pH, promoting the formation of hydrolyzed species. Results between the laboratories are compared in terms of the number of decay components, luminescence lifetimes, and spectral band positions. The successes and limitations of TRES in uranyl analysis and speciation in aqueous solutions are discussed.
The hydration process of Portland cement in a cementitious system is crucial for development of the high‐quality cement‐based construction material. Complementary experiments of X‐ray diffraction analysis (XRD), scanning electron microscopy (SEM) and time‐resolved laser fluorescence spectroscopy (TRLFS) using europium (Eu(III)) as an optical probe are used to analyse the hydration process of two cement systems in the absence and presence of different organic admixtures. We show that different analysed admixtures and the used sulphate carriers in each cement system have a significant influence on the hydration process, namely on the time‐dependence in the formation of different hydrate phases of cement. Moreover, the effect of a particular admixture is related to the type of sulphate carrier used. The quantitative information on the amounts of the crystalline cement paste components is accessible via XRD analysis. Distinctly different morphologies of ettringite and calcium−silicate−hydrates (C−S−H) determined by SEM allow visual conclusions about formation of these phases at particular ageing times. The TRLFS data provides information about the admixture influence on the course of the silicate reaction. The dip in the dependence of the luminescence decay times on the hydration time indicates the change in the structure of C−S−H in the early hydration period. Complementary information from XRD, SEM and TRLFS provides detailed information on distinct periods of the cement hydration process.
The hydration process of Portland cement in a cementitious system is crucial for development of the high‐quality cement‐based construction material. Complementary experiments of X‐ray diffraction analysis (XRD), scanning electron microscopy (SEM) and time‐resolved laser fluorescence spectroscopy (TRLFS) using europium (Eu(III)) as an optical probe are used to analyse the hydration process of two cement systems in the absence and presence of different organic admixtures. We show that different analysed admixtures and the used sulphate carriers in each cement system have a significant influence on the hydration process, namely on the time‐dependence in the formation of different hydrate phases of cement. Moreover, the effect of a particular admixture is related to the type of sulphate carrier used. The quantitative information on the amounts of the crystalline cement paste components is accessible via XRD analysis. Distinctly different morphologies of ettringite and calcium−silicate−hydrates (C−S−H) determined by SEM allow visual conclusions about formation of these phases at particular ageing times. The TRLFS data provides information about the admixture influence on the course of the silicate reaction. The dip in the dependence of the luminescence decay times on the hydration time indicates the change in the structure of C−S−H in the early hydration period. Complementary information from XRD, SEM and TRLFS provides detailed information on distinct periods of the cement hydration process.
The luminescence of Lanthanide(Ill) complexes with different model ligands was studied under direct as well as sensitized excitation conditions. The research was performed in the context of studies dealing with deep-underground storages for high-level nuclear waste. Here, Lanthanide(III) ions served as natural analogues for Actinide(III) ions and the low-molecular weight organic ligands are present in clay minerals and furthermore, they were employed as proxies for building blocks of humic substances, which are important complexing molecules in the natural environment, e.g., in the far field of a repository site. Time-resolved luminescence spectroscopy was applied for a detailed characterization of Eu(III), Tb(III), Sm(III) and.Dy(III) complexes in aqueous solutions. Based on the observed luminescence the ligands were tentatively divided into two groups (A, B). The luminescence of Lanthanide(III) complexes of group A was mainly influenced by an energy transfer to OH-vibrations. Lanthanide(Ill) complexes of group B showed ligand-related luminescence quenching, which was further investigated. To gain more information on the underlying quenching processes of group A and B ligands, measurements at different temperatures (77 K <= T <= 353 K) were performed and activation energies were determined based on an Arrhenius analysis. Moreover, the influence of the ionic strength between 0 M <= 1 <= 4 M on the Lanthanide(III) luminescence was monitored for different complexes, in order to evaluate the influence of specific conditions encountered in host rocks foreseen as potential repository sites.
In this study, the apparent relationship between the transport process and the surface chemistry of the Calcium-Silicate Hydrate (CSH) phases was investigated. For this purpose, a method was developed to synthesize ultrathin CSH phases to be used as a model substrate with the specific modification of their structure by introducing europium (Eu(III)). The structural and chemical changes during this Eu(III)-doping were observed by means of infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), and time-resolved laser fluorescence spectroscopy (TRLFS). These alterations of the CSH phases led to significant changes in the surface chemistry and consequently to considerable variations in the interaction with water, as evidenced by measurements of the contact angles on the modified model substrates. Our results provide the basis for a more profound molecular understanding of reactive transport processes in cement-based systems. Furthermore, these results broaden the perspective of improving the stability of cement-based materials, which are subjected to the impact of aggressive aqueous environments through targeted modifications of the CSH phases.
Gadolinium-doped ceria or gadolinium-stabilized ceria (GDC) is an important technical material due to its ability to conduct O2- ions, e.g., used in solid oxide fuel cells operated at intermediate temperature as an electrolyte, diffusion barrier, and electrode component. We have synthesized Ce1-xGdxO2-y:Eu3+ (0 <= x <= 0.4) nanoparticles (11-15 nm) using a scalable spray pyrolysis method, which allows the continuous large-scale technical production of such materials. Introducing Eu3+ ions in small amounts into ceria and GDC as spectroscopic probes can provide detailed information about the atomic structure and local environments and allows us to monitor small structural changes. This study presents a novel approach to structurally elucidate europium-doped Ce1-xGdxO2-y:Eu3+ nanoparticles by way of Eu3+ spectroscopy, processing the spectroscopic data with the multiway decomposition method parallel factor (PARAFAC) analysis. In order to perform the deconvolution of spectra, data sets of excitation wavelength, emission wavelength, and time are required. Room temperature, time-resolved emission spectra recorded at lambda(ex) = 464 nm show that Gd3+ doping results in significantly altered emission spectra compared to pure ceria. The PARAFAC analysis for the pure ceria samples reveals a high-symmetry species (which can also be probed directly via the CeO2 charge transfer band) and a low-symmetry species. The GDC samples yield two low-symmetry spectra in the same experiment. High-resolution emission spectra recorded under cryogenic conditions after probing the D-5(0)-F-7(0) transition at lambda(ex) = 575-583 nm revealed additional variation in the low-symmetry Eu3+ sites in pure ceria and GDC. The total luminescence spectra of CeO2-y:Eu3+ showed Eu3+ ions located in at least three slightly different coordination environments with the same fundamental symmetry, whereas the overall hypsochromic shift and increased broadening of the D-5(0)-F-7(0) excitation in the GDC samples, as well as the broadened spectra after deconvolution point to less homogeneous environments. The data of the Gd3+-containing samples indicates that the average charge density around the Eu3+ ions in the lattice is decreased with increasing Gd3+ and oxygen vacancy concentration. For reference, the Judd-Ofelt parameters of all spectra were calculated. PARAFAC proves to be a powerful tool to analyze lanthanide spectra in crystalline solid materials, which are characterized by numerous Stark transitions and where measurements usually yield a superposition of different contributions to any given spectrum.
Lanthanide based ceria nanomaterials are important practical materials due to the redox properties that are useful in the avenues pertaining to technology and life sciences. Sub 10 nm spherical and highly monodisperse Ce1−xYbxO2−y (0.04 ≤ x ≤ 0.22) nanoparticles were synthesized by thermal decomposition, annealed separately at 773 K and 1273 K for 2 hours and characterized. Elemental mapping for Yb3+ doped ceria nanoparticles shows homogeneous distribution of Yb3+ atoms in the ceria with low Yb3+ content annealed at 773 K and 1273 K for 2 hours. However, clusters are observed for 773 K annealed ceria samples with high concentration of Yb3+. These clusters are not detected in 1273 K annealed nanomaterials. Introducing small amounts of Yb3+ ions into the ceria lattice as spectroscopic probes can provide detailed information about the atomic structure and local environments allowing the monitoring of small structural changes, such as clustering. The emission spectra observed at room temperature and at 4 K have a manifold of bands that corresponds to the 2F5/2 → 2F7/2 transition of Yb3+ ions. Some small shifts are observed in the Stark splitting pattern depending on the sample and the annealing conditions. The deconvolution by PARAFAC analysis yielded luminescence decay kinetics as well as the associated luminescence spectra of three species for each of the low Yb3+ doped ceria samples annealed at 773 K and one species for the 1273 K annealed samples. However, the ceria samples with high concentration of Yb3+ annealed at the two temperatures showed only one species with lower decay times as compared to the low Yb3+ doped ceria samples.
Ammonium serves as key nitrogen source and metabolic intermediate, yet excess causes toxicity. Ammonium uptake is mediated by ammonium transporters, whose regulation is poorly understood. While transport can easily be characterized in heterologous systems, measuring transporter activity in vivo remains challenging. Here we developed a simple assay for monitoring activity in vivo by inserting circularly-permutated GFP into conformation-sensitive positions of two plant and one yeast ammonium transceptors (’AmTrac and ’MepTrac’). Addition of ammonium to yeast cells expressing the sensors triggered concentration dependent fluorescence intensity (FI) changes that strictly correlated with the activity of the transporter. Fluorescence-based activity sensors present a novel technology for monitoring the interaction of the transporters with their substrates, the activity of transporters and their regulation in vivo, which is particularly valuable in the context of analytes for which no radiotracers exist, as well as for cell-specific and subcellular transport processes that are otherwise difficult to track.
The adsorption of boron (boric acid) from aqueous solutions on alumina has been investigated at pH 8.0, I=0.1M NaClO4, T=22 +/- 3 degrees C, and under normal atmospheric conditions. The characterization of the adsorbed species was performed by Raman spectroscopy and the spectroscopic speciation was assisted by theoretical DFT calculations. Evaluation of the spectroscopic data points to the formation of inner-sphere surface complexes and indicates the formation of two different types of adsorbed boron species. The theoretical calculations corroborate the spectroscopic data and indicate that at low boron concentration the monodentate surface species dominates, whereas increased boron concentration favors the formation of a bidentate surface species. Assuming low coverage, the conditional formation constant for the monodentate surface species has been evaluated to be log=4.1 +/- 0.1.
The retention of actinides in different oxidation states (An(X), X = III, IV, VI) by a calcium-silicate-hydrate (C-S-H) phase with a Ca/Si (C/S) ratio of 0.8 was investigated in the presence of gluconate (GLU). The actinides considered were Am(III), Th(IV), Pu(IV), and U(VI). Eu(III) was investigated as chemical analogue for Am(III) and Cm(III). In addition to the ternary systems An(X)/GLU/C-S-H, also binary systems An(X)/C-S-H, GLU/C-S-H, and An(X)/GLU were studied. Complementary analytical techniques were applied to address the different specific aspects of the binary and ternary systems. Time-resolved laser-induced luminescence spectroscopy (TRLFS) was applied in combination with parallel factor analysis (PARAFAC) to identify retained species and to monitor species-selective sorption kinetics. ¹³C and ²⁹Si magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were applied to determine the bulk structure and the composition of the C-S-H surface, respectively, in the absence and presence of GLU. The interaction of Th(IV) with GLU in different electrolytes was studied by capillary electrophoresis-inductively coupled plasma mass spectrometry (CE-ICP-MS). The influence of GLU on An(X) retention was investigated for a large concentration range up to 10⁻² M. The results showed that GLU had little to no effect on the overall An(X) retention by C-S-H with C/S of 0.8, regardless of the oxidation state of the actinides. For Eu(III), the TRLFS investigations additionally implied the formation of a Eu(III)-bearing precipitate with dissolved constituents of the C-S-H phase, which becomes structurally altered by the presence of GLU. For U(VI) sorption on the C-S-H phase, only a small influence of GLU could be established in the luminescence spectroscopic investigations, and no precipitation of U(VI)-containing secondary phases could be identified.
The retention of actinides in different oxidation states (An(X), X = III, IV, VI) by a calcium-silicate-hydrate (C-S-H) phase with a Ca/Si (C/S) ratio of 0.8 was investigated in the presence of gluconate (GLU). The actinides considered were Am(III), Th(IV), Pu(IV), and U(VI). Eu(III) was investigated as chemical analogue for Am(III) and Cm(III). In addition to the ternary systems An(X)/GLU/C-S-H, also binary systems An(X)/C-S-H, GLU/C-S-H, and An(X)/GLU were studied. Complementary analytical techniques were applied to address the different specific aspects of the binary and ternary systems. Time-resolved laser-induced luminescence spectroscopy (TRLFS) was applied in combination with parallel factor analysis (PARAFAC) to identify retained species and to monitor species-selective sorption kinetics. ¹³C and ²⁹Si magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were applied to determine the bulk structure and the composition of the C-S-H surface, respectively, in the absence and presence of GLU. The interaction of Th(IV) with GLU in different electrolytes was studied by capillary electrophoresis-inductively coupled plasma mass spectrometry (CE-ICP-MS). The influence of GLU on An(X) retention was investigated for a large concentration range up to 10⁻² M. The results showed that GLU had little to no effect on the overall An(X) retention by C-S-H with C/S of 0.8, regardless of the oxidation state of the actinides. For Eu(III), the TRLFS investigations additionally implied the formation of a Eu(III)-bearing precipitate with dissolved constituents of the C-S-H phase, which becomes structurally altered by the presence of GLU. For U(VI) sorption on the C-S-H phase, only a small influence of GLU could be established in the luminescence spectroscopic investigations, and no precipitation of U(VI)-containing secondary phases could be identified.
Vibrationally resolved fluorescence spectra of four angular [N]phenylenes were recorded with laser excited Shpol’skii spectroscopy (LESS) in an n-octane matrix at 10 K. In general, the same vibrational frequencies were observed in the fluorescence excitation and emission spectra, indicating that the geometries of ground and electronically excited state are very similar. Because of intensity borrowing from the S2 state, vibrations of two different symmetries were observed in the fluorescence excitation spectra of angular [3]phenylene and zig-zag[5]phenylene. This finding allowed the location of the S2 state for these compounds. DFT calculations(RB3LYP/6-31G*) of the ground state vibrational frequencies were made. The calculated vibrational modes were in reasonably good agreement with the experimental data. A new very low-frequency vibration of approximately 100 cm-1 was predicted and experimentally confirmed for all [N]phenylenes investigated. This vibration seems to be unique for [N]phenylenes and is attributed to an in-plane movement of the carbon backbone.
Deuteration effects on the vibronic structure of the emission and excitation spectra of triangular [4]phenylene (D3h[4]phenylene) were studied using laser-excited Shpolskii spectroscopy (LESS) in an octane matrix at 4.2 K. For correct assignment of the vibrational modes, the experimental results were compared with calculated frequencies (B3LYP/6-31G*). CH vibrations were identified by their characteristic isotopic shifts in the spectra of deuterated triangular [4]phenylenes. Two CC stretching modes, at 100 cm–1 and 1176 cm–1, suitable as probes for bond strength changes in the excited state, were identified. The isotope effect on the internal conversion rates of triangular [4]phenylene was evaluated from measurements of temperature dependent lifetime. Isotope dependency and the magnitude of the internal conversion rates indicate that internal conversion in triangular [4]phenylene is most likely induced by CH vibrations. The results obtained by LESS and lifetime measurements were compared with PM3 PECI calculations of the excited state structure. The theoretical results and the relation between ground and excited state vibration energies of the 1176 cm–1 probe vibration indicate a reduction of bond alternation of the central cyclohexatriene ring in the excited state.
Deuteration effects on the vibronic structure of the emission and excitation spectra of triangular [ 4] phenylene (D-3h [4]phenylene) were studied using laser-excited Shpol'skii spectroscopy (LESS) in an octane matrix at 4.2 K. For correct assignment of the vibrational modes, the experimental results were compared with calculated frequencies (B3LYP/6-31G*). CH vibrations were identified by their characteristic isotopic shifts in the spectra of deuterated triangular [4]phenylenes. Two CC stretching modes, at 100 cm(-1) and 1176 cm(-1), suitable as probes for bond strength changes in the excited state, were identified. The isotope effect on the internal conversion rates of triangular [4] phenylene was evaluated from measurements of temperature dependent lifetime. Isotope dependency and the magnitude of the internal conversion rates indicate that internal conversion in triangular [4] phenylene is most likely induced by CH vibrations. The results obtained by LESS and lifetime measurements were compared with PM3 PECI calculations of the excited state structure. The theoretical results and the relation between ground and excited state vibration energies of the 1176 cm(-1) probe vibration indicate a reduction of bond alternation of the central cyclohexatriene ring in the excited state
Encapsulation of diagnostic and therapeutic compounds in transporters improves their delivery to the point of need. An even more efficient treatment of diseases can be achieved using carriers with targeting or protecting moieties. In the present work, we investigated micellar and liposomal nanocarriers modified with fluorescein, peptides, and polymers that are covalently bound to fatty acids or phospholipids to ensure a self-driven incorporation into the micelles or liposomes. First, we characterized the photophysics of the fluorescent probes in the absence and in the presence of nanocarriers. Changes in the fluorescence decay time, quantum yield, and intensity of a fluorescein-labeled fatty acid (fluorescein-labeled palmitic acid [fPA]) and a fluorescein-labeled lipopeptide (P2fA2) were found. By exploiting these changes, we investigated a lipopeptide (P2A2 as an uptake-mediating unit) in combination with different nanocarriers (micelles and liposomes) and determined the corresponding association constant K-ass values, which were found to be very high. In addition, the mobility of fPA was exploited using fluorescence correlation spectroscopy (FCS) and fluorescence depolarization (FD) experiments to characterize the nanocarriers. Cellular uptake experiments with mouse brain endothelial cells provided information on the uptake behavior of liposomes modified by uptake-mediating P2A2 and revealed differences in the uptake behavior between pH-sensitive and pH-insensitive liposomes.
Nowadays, the encapsulation of therapeutic compounds in so-called carrier systems is a very smart method to achieve protection as well as an improvement of their temporal and spatial distribution. After the successful transport to the point of care, the delivery has to be released under controlled conditions. To monitor the triggered release from the carrier, we investigated different fluorescent probes regarding their response to the pH-induced collapse of pH-sensitive liposomes (pHSLip), which occurs when the environmental pH falls below a critical value. Depending on the probe, the fluorescence decay time as well as fluorescence anisotropy can be used equally as key parameters for monitoring the collapse. Especially the application of a fluorescein labeled fatty acid (fPA) enabled the monitoring of the pHSLips collapse and the pH of its microenvironment simultaneously without interference. Varying the pH in the range of 3 < pH < 9, anisotropy data revealed the critical pH value at which the collapse of the pHSLips occurs. Complementary methods, e.g., fluorescence correlation spectroscopy and dynamic light scattering, supported the analysis based on the decay time and anisotropy. Additional experiments with varying incubation times yielded information on the kinetics of the liposomal collapse.
Oligospirothioketal (OSTK) rods are presented as an adjustable scaffold for optical membrane probes. The OSTK rods are readily incorporated into lipid bilayers due to their hydrophobic backbones. Because of their high length-over-diameter aspect ratio, only a minimal disturbance of the lipid bilayer is caused. OSTK rods show outstanding rigidity and allow defined labeling with fluorescent dyes, yielding full control of the orientation between the dye and OSTK skeleton. This. allows the construction of novel Forster resonance energy transfer probes with highly defined relative orientations of the transition dipole moments of the donor and acceptor dyes and makes the class of OSTK probes a power-fill, flexible toolbox for optical biosensing applications. Data on steady-state and time-resolved fluorescence experiments investigating the incorporation of coumarin- and [1,3]-dioxolo[4,5-f][1,3]benzo-dioxole-labeled OSTKs in large unilamellar vesicles are presented as a show case.
Characterization of interactions between antigens and antibodies is of utmost importance both for fundamental understanding of the binding and for development of advanced clinical diagnostics. Here, fluorescence line-narrowing (FLN) spectroscopy was used to study physicochemical interactions between 3-hydroxybenzo[a]pyrene (3OH-BaP, as antigen) and a variety of solvent matrices (as model systems) or anti-polycyclic aromatic hydrocarbon antibodies (anti-PAH). We focused the studies on the specific physicochemical interactions between 3OH-BaP and different, previously obtained, monoclonal and recombinant anti-PAH antibodies. Control experiments performed with non-binding monoclonal antibodies and bovine serum albumin (BSA) indicated that nonspecific interactions did not affect the FLN spectrum of 3OH-BaP. The spectral positions and relative intensities of the bands in the FLN spectra are highly dependent on the molecular environment of the 3OH-BaP. The FLN bands correlate with different vibrational modes of 3OH-BaP which are affected by interactions with the molecular environment (pi-pi interactions, H-bonding, or van-der-Waals forces). Although the analyte (3OH-BaP) was the same for all the antibodies investigated, different binding interactions could be identified from the FLN spectra on the basis of structural flexibility and conformational multiplicity of the antibodies' paratopes.
Immunochemical analytical methods are very successful in clinical diagnostics and are nowadays also emerging in the control of food as well as monitoring of environmental issues. Among the different immunoassays, luminescence based formats are characterized by their outstanding sensitivity making this format especially attractive for future applications. The need for multiparameter detection capabilities calls for a tool box of dye labels in order to transduce the biochemical reaction into an optically detectable signal. Here, in a multiparameter approach each analyte may be detected by a different dye with a unique emission color (covering the blue to red spectral range) or a unique luminescence decay kinetics. In the case of a competitive immunoassay format for each of the different dye labels an individual antibody would be needed. In the present paper a slightly modified approach is presented using a 7-aminocoumarin unit as the basic antigen against which highly specific antibodies were generated. Leaving the epitope region in the dyes unchanged but introducing a side group in positon 3 of the coumarin system allowed us to tune the optical properties of the coumarin dyes without the necessity of new antibody generation. Upon modification of the parent coumarin unit the full spectral range from blue to deep red was accessed. In the manuscript the photophysical characterization of the coumarin derivatives and their corresponding immunocomplexes with two highly specific antibodies is presented. The coumarin dyes and their immunocomplexes were characterized by steady-state and time-resolved absorption as well as emission spectroscopy. Moreover, fluorescence depolarization measurements were carried out to complement the data stressing the different binding modes of the two antibodies. The binding modes were evaluated using the photophysics of 7-aminocoumarins and how it was affected in the respective immunocomplexes, namely, the formation of the intramolecular charge transfer (ICT) as well as the twisted intramolecular charge transfer (TICT). In contrast to other antibody-dye pairs reported a distinct fluorescence enhancement upon formation of the antibody-dye complex up to a factor of SO was found. Because of the easy emission color tuning by tailoring the coumarin substitution for the antigen binding in nonrelevant position 3 of the parent molecule, a dye tool box is on hand which can be used in the construction of competitive multiparameter fluorescence enhancement immunoassays (FenIA).
Bright or dark immune complexes of anti-TAMRA antibodies for adapted fluorescence-based bioanalysis
(2015)
Fluorescence labels, for example fluorescein or rhodamin derivatives, are widely used in bioanalysis applications including lateral-flow assays, PCR, and fluorescence microscopy. Depending on the layout of the particular application, fluorescence quenching or enhancement may be desired as the detection principle. Especially for multiplexed applications or high-brightness requirements, a tunable fluorescence probe can be beneficial. The alterations in the photophysics of rhodamine derivatives upon binding to two different anti-TAMRA antibodies were investigated by absorption and fluorescence-spectroscopy techniques, especially determining the fluorescence decay time and steady-state and time-resolved fluorescence anisotropy. Two monoclonal anti-TAMRA antibodies were generated by the hybridoma technique. Although surface-plasmon-resonance measurements clearly proved the high affinity of both antibodies towards 5-TAMRA, the observed effects on the fluorescence of rhodamine derivatives were very different. Depending on the anti-TAMRA antibody either a strong fluorescence quenching (G71-DC7) or a distinct fluorescence enhancement (G71-BE11) upon formation of the immune complex was observed. Additional rhodamine derivatives were used to gain further information on the binding interaction. The data reveal that such haptens as 5-TAMRA could generate different paratopes with equal binding affinities but different binding interactions, which provide the opportunity to adapt bioanalysis methods including immunoassays for optimized detection principles for the same hapten depending on the specific requirements.
Optical methods play an important role in process analytical technologies (PAT). Four examples of optical process and quality sensing (OPQS) are presented, which are based on three important experimental techniques: near-infrared absorption, luminescence quenching, and a novel method, photon density wave (PDW) spectroscopy. These are used to evaluate four process and quality parameters related to beer brewing and polyurethane (PU) foaming processes: the ethanol content and the oxygen (O2) content in beer, the biomass in a bioreactor, and the cellular structures of PU foam produced in a pilot production plant.
Optical methods play an important role in process analytical technologies (PAT). Four examples of optical process and quality sensing (OPQS) are presented, which are based on three important experimental techniques: near- infrared absorption, luminescence quenching, and a novel method, photon density wave (PDW) spectroscopy. These are used to evaluate four process and quality parameters related to beer brewing and polyurethane (PU) foaming processes: the ethanol content and the oxygen (O-2) content in beer, the biomass in a bioreactor, and the cellular structures of PU foam produced in a pilot production plant
Die Anwendung von optischen Parametern zur Stoffcharakterisierung wird diskutiert. Dabei ist der Schwerpunkt der Diskussion auf absorptions- und fluoreszenzspektroskopische Methoden gesetzt. Beide Methoden können schnell und zuverlässig – auch im on-line Betrieb – eingesetzt werden. Der Beitrag soll einen Überblick über die grundlegenden Möglichkeiten der Anwendung beider Methoden geben.
Time-resolved emission data (fluorescence decay and fluorescence depolarization) of two three-color Forster resonance energy transfer (tc-FRET) systems consisting of a carbostyril donor (D), a ruthenium complex (Ru) as relay dye, and a Cy5 derivative (Cy) or, optionally, an anthraquinone quencher (Q) were carefully analyzed using advanced distribution analysis models. Thereby, it is possible to get information on the flexibility and mobility of the chromophores which are bound to double stranded (ds) DNA. Especially the distance distribution based on the analysis of the fluorescence depolarization is an attractive approach to complement data of fluorescence decay time analysis. The distance distributions extracted from the experimental data were in excellent agreement with those determined from accessible volume (AV) simulations. Moreover, the study showed that for tc-FRET systems the combination of dyes emitting on different time scales (e.g., nanoseconds vs microseconds) is highly beneficial in the distribution analysis of time-resolved luminescence data in cases where macromolecules such as DNA are involved. Here, the short lifetimes can yield information on the rotation of the dye molecule itself and the long lifetime can give insight in the overall dynamics of the macromolecule.
The transport of bioactive compounds to the site of action is a great challenge. A promising approach to overcome application-related problems is the development of targeting colloidal transport systems, such as micelles which are equipped with uptake mediating moieties. Here, we investigated a set of novel lipopeptides which exhibit a surfactant-like structure due to attachment of two palmitoyl chains to the Nterminus of cationic or anionic amino acid sequences. We analyzed the association behavior of these lipopeptides by using 5(6)-carboxyfluorescein (CF)-labeled derivatives as a fluorescent probe and different spectroscopic methods such as fluorescence anisotropy and fluorescence correlation spectroscopy (FCS). The photophysical properties as well as the diffusion and rotational movements of the CF-labeled lipopeptides were exploited to determine the cmc and the size of the micelles consisting of lipopeptides. We could distinguish cationic and anionic lipopeptides by their association behavior and by studying the interactions with mouse brain capillary endothelial cells (b.end3). The cationic derivatives turned out to be very strong surfactants with a very low cmc in the micromolar range (0.5-14 mu M). The unique combination of micelle-forming property and cell-penetrating ability can pave the road for the development of a novel class of efficient drug carrier systems.
The standard procedure in the lab for plasmid isolation usually involves a 2-mL, 16 h over-night cultivation in 15-mL bioreaction tubes in LB medium. This is time consuming, and not suitable for high-throughput applications. This study shows that it is possible to produce plasmid DNA (pDNA) in a 1.5-mL microcentrifuge tube with only 100 L cultivation volume in less than 7 h with a simple protocol. Compared with the standard LB cultivation for pDNA production reaching a final pDNA concentration range of 1.5-4 mu g mL(-1), a 6- to 10-fold increase in plasmid concentration (from 10 up to 25 mu g mL(-1) cultivation volume) is achieved using an optimized medium with an internal substrate delivery system (EnBase (R)). Different strains, plasmids, and the applicability of different inoculation tools (i.e. different starting ODs) were compared, demonstrating the robustness of the system. Additionally, dissolved oxygen was monitored in real time online, indicating that under optimized conditions oxygen limitation can be avoided. We developed a simple protocol with a significantly decreased procedure time, enabling simultaneous handling of more samples, while a consistent quality and a higher final pDNA concentration are ensured.
Quenching mechanism of uranyl(VI) by chloride and bromide in aqueous and non-aqueous solutions
(2021)
A major hindrance in utilizing uranyl(VI) luminescence as a standard analytical tool, for example, in environmental monitoring or nuclear industries, is quenching by other ions such as halide ions, which are present in many relevant matrices of uranyl(VI) speciation. Here, we demonstrate through a combination of time-resolved laser-induced fluorescence spectroscopy, transient absorption spectroscopy, and quantum chemistry that coordinating solvent molecules play a crucial role in U(VI) halide luminescence quenching. We show that our previously suggested quenching mechanism based on an internal redox reaction of the 1:2-uranyl-halide-complex holds also true for bromide-induced quenching of uranyl(VI). By adopting specific organic solvents, we were able to suppress the separation of the oxidized halide ligand X-2(center dot-) and the formed uranyl(V) into fully solvated ions, thereby "reigniting" U(VI) luminescence. Time-dependent density functional theory calculations show that quenching occurs through the outer-sphere complex of U(VI) and halide in water, while the ligand-to-metal charge transfer is strongly reduced in acetonitrile.
9,10-substituted anthracenes are known for their useful optical properties like fluorescence, which makes them frequently used probes in sensing applications. In this article, we investigate the fundamental photophysical properties of three pyridyl-substituted variants. The nitrogen atoms in the pyridinium six-membered rings are located in the ortho-, meta-, and para-positions in relation to the anthracene core. Absorption, fluorescence, and transient absorption measurements were carried out and were complemented by theoretical calculations. We monitored the photophysics of the anthracene derivatives in chloroform and water investigating the protonated as well as their nonprotonated forms. We found that the optical properties of the nonprotonated forms are strongly determined by the anthracene chromophore, with only small differences to other 9,10-substituted anthracenes, for example diphenyl anthracene. In contrast, protonation leads to a strong decrease in fluorescence intensity and lifetime. Transient absorption measurements and theoretical calculations revealed the formation of a charge-transfer state in the protonated chromophores, where electron density is shifted from the anthracene moiety toward the protonated pyridyl substituents. While the para- and ortho-derivatives' charge transfer is still moderately fluorescent, the meta-derivative is affected much stronger and shows nearly no fluorescence. This nitrogen-atom-position-dependent sensitivity to hydronium activity makes a combination of these fluorophores very attractive for pH-sensing applications covering a broadened pH range.
The so-called DBD ([1,3]dioxolo[4,5-f][1,3]benzodioxole) dyes are a new class of fluorescent dyes, with tunable photophysical properties like absorption, fluorescence lifetime, and Stokes shift. With the development of sulfur based DBDs, this dye class is extended even further for possible applications in spectroscopy and microscopy. In this paper we are investigating the basic photophysical properties and their implications for future applications for S-4-DBD as well as O-4-DBD. On the basis of time-resolved laser fluorescence spectroscopy, transient absorption spectroscopy, and UV/vis-spectroscopy, we determined the rate constants of the radiative and nonradiative deactivation processes as well as the energy of respective electronic states involved in the electronic deactivation of S-4-DBD and of O-4-DBD. For S-4-DBD we unraveled the triplet formation with intersystem crossing quantum yields of up to 80%. By TD-DFT calculations we estimated a triplet energy of around 13500-14700 cm(-1) depending on the DBD dye and solvent. Through solvent dependent measurements, we found quadrupole moments in the range of 2 B.
A new generation of wavelength-tunable, fluorescent dyes, so-called DBD ([1,3]dioxolo[4,5-f][1,3]benzodioxole) dyes, were developed a few years ago, and they showed great potential as probes, for example, for fluorescence microscopy. However, their photophysics is not fully explored and leaves open questions regarding their large fluorescence Stokes shifts and sensitivity to solvent conditions of differently substituted DBD dyes. To improve the understanding of the influence of the substitution pattern of the DBD dyes on their respective photophysics, transient absorption spectroscopy (TAS) was used, that is, a pump-probe experiment on the femtosecond timescale. TAS allows measurements of excited states, ground state recovery, solvent relaxation, and fluorescence properties on time scales of up to several nanoseconds. Two different DBD dye samples were investigated: aryl- and ester-substituted DBD dyes. Experiments were carried out in solvents with different polarities using different excitation energies and at different viscosities. Based on the experimental data and theoretical calculations, we were able to determine the conformational changes of the molecule due to electronic excitation and were able to investigate solvent relaxation processes for both types of DBD dyes. By generalizing the theory for quadrupole-induced solvent relaxation developed by Togashi et al., we derived quadrupole moments of both molecules in the ground and excited state. Our data showed differences in the binding of polar solvent molecules to the dyes depending on the substituent on the DBD dye. In the case of water as the solvent, an additional efficient quenching process in the electronically excited state was revealed, which was indicated by the observation of solvated electrons in the TAS signals.
For the only water coordinated "free" uranyl (VI) aquo ion in perchlorate solution we identified and assigned several different excited states and showed that the (3)Delta state is the luminescent triplet state from transient absorption spectroscopy. With additional data from other spectroscopic methods (TRLFS, UV/vis) we generated a detailed Jablonski diagram and determined rate constants for several state transitions, like the inner conversion rate constant from the (3)Phi state to the (3)Delta state transition to be 0.35 ps(-1). In contrast to luminescence measurements, it was possible to observe the highly quenched uranyl(VI) ion in highly concentrated chloride solution by TAS and we were able to propose a dynamic quenching mechanism, where chloride complexation is followed by the charge transfer from the excited state uranyl(VI) to chloride. This proposed quenching route is supported by TD-DFT calculations.
Rapid Synthesis of Sub-10nm Hexagonal NaYF4-Based Upconverting Nanoparticles using Therminol((R))66
(2018)
We report a simple one-pot method for the rapid preparation of sub-10nm pure hexagonal (-phase) NaYF4-based upconverting nanoparticles (UCNPs). Using Therminol((R))66 as a co-solvent, monodisperse UCNPs could be obtained in unusually short reaction times. By varying the reaction time and reaction temperature, it was possible to control precisely the particle size and crystalline phase of the UCNPs. The upconversion (UC) luminescence properties of the nanocrystals were tuned by varying the concentrations of the dopants (Nd3+ and Yb3+ sensitizer ions and Er3+ activator ions). The size and phase-purity of the as-synthesized core and core-shell nanocrystals were assessed by using complementary transmission electron microscopy, dynamic light scattering, X-ray diffraction, and small-angle X-ray scattering studies. In-depth photophysical evaluation of the UCNPs was pursued by using steady-state and time-resolved luminescence spectroscopy. An enhancement in the UC intensity was observed if the nanocrystals, doped with optimized concentrations of lanthanide sensitizer/activator ions, were further coated with an inert/active shell. This was attributed to the suppression of surface-related luminescence quenching effects.
Rapid synthesis of sub-10 nm hexagonal NaYF4-based upconverting nanoparticles using Therminol® 66
(2018)
We report a simple one-pot method for the rapid preparation of sub-10nm pure hexagonal (-phase) NaYF4-based upconverting nanoparticles (UCNPs). Using Therminol((R))66 as a co-solvent, monodisperse UCNPs could be obtained in unusually short reaction times. By varying the reaction time and reaction temperature, it was possible to control precisely the particle size and crystalline phase of the UCNPs. The upconversion (UC) luminescence properties of the nanocrystals were tuned by varying the concentrations of the dopants (Nd3+ and Yb3+ sensitizer ions and Er3+ activator ions). The size and phase-purity of the as-synthesized core and core-shell nanocrystals were assessed by using complementary transmission electron microscopy, dynamic light scattering, X-ray diffraction, and small-angle X-ray scattering studies. In-depth photophysical evaluation of the UCNPs was pursued by using steady-state and time-resolved luminescence spectroscopy. An enhancement in the UC intensity was observed if the nanocrystals, doped with optimized concentrations of lanthanide sensitizer/activator ions, were further coated with an inert/active shell. This was attributed to the suppression of surface-related luminescence quenching effects.
In the study a dyad (C6 probe), constructed of two dyes with highly different hydrophobicities, was investigated by steady-state and time-resolved spectroscopic techniques in chloroform, methanol, and in phospholipid vesicles, respectively. The dyad was built on two dyes: the lipophilic benzo[a]pyrene (BaP) and the hydrophilic sulforhodamine B (SRB). The dyes were linked via a short, but flexible alkyl chain (six C-atoms). Based on their spectroscopic properties, BaP and SRB showed a very efficient non-radiative resonance energy transfer in solution. Incorporation into a lipid bilayer limited the relative flexibility (degree of freedom) between donor and acceptor and was used for the investigation of fundamental photophysical aspects (especially of FRET) as well as to elucidate the potential of the dyad to probe the interface of vesicles (or cells). The location of the two dyes in vesicles and their respective accessibility for interactions with dye-specific antibodies was investigated. Based on the alteration of the anisotropy, on the rotational correlation time as well as on the diffusion coefficient the incorporation of the C6 probe into the vesicles was evaluated. Especially the limitation in the relative movements of the two dyes was considered and used to differentiate between potential parameters, that influence the energy transfer in the dyad. Transient absorption spectroscopy (TAS) and pulsed-interleave single molecule fluorescence experiments were performed to better understand the intramolecular interactions in the dyad. Finally, in a showcase for a biosensing application of the dyads, the binding of an SRB-specific antibody was investigated when the dyad was incorporated in vesicles.
Different signal amplification strategies to improve the detection sensitivity of immunoassays have been applied which utilize enzymatic reactions, nanomaterials, or liposomes. The latter are very attractive materials for signal amplification because liposomes can be loaded with a large amount of signaling molecules, leading to a high sensitivity. In addition, liposomes can be used as a cell-like "bioscaffold" to directly test recognition schemes aiming at cell-related processes. This study demonstrates an easy and fast approach to link the novel hydrophobic optical probe based on [1,3]dioxolo[4,5-f]-[1,3]benzodioxole (DBD dye mm239) with tunable optical properties to hydrophilic recognition elements (e.g., antibodies) using liposomes for signal amplification and as carrier of the hydrophobic dye. The fluorescence properties of mm239 (e.g., long fluorescence lifetime, large Stokes shift, high photostability, and high quantum yield), its high hydrophobicity for efficient anchoring in liposomes, and a maleimide bioreactive group were applied in a unique combination to build a concept for the coupling of antibodies or other protein markers to liposomes (coupling to membranes can be envisaged). The concept further allowed us to avoid multiple dye labeling of the antibody. Here, anti-TAMRA-antibody (DC7-Ab) was attached to the liposomes. In proof-of-concept, steady-state as well as time-resolved fluorescence measurements (e.g., fluorescence depolarization) in combination with single molecule detection (fluorescence correlation spectroscopy, FCS) were used to analyze the binding interaction between DC7-Ab and liposomes as well as the binding of the antigen rhodamine 6G (R6G) to the antibody. Here, the Forster resonance energy transfer (FRET) between mm239 and R6G was monitored. In addition to ensemble FRET data, single-molecule FRET (PIE-FRET) experiments using pulsed interleaved excitation were used to characterize in detail the binding on a single-molecule level to avoid averaging out effects.
We report on a new three-color FRET system consisting of three fluorescent dyes, i.e., of a carbostyril (=quinolin-2(1H)-one)-derived donor D, a (bathophenanthroline)ruthenium complex as a relay chromophore A1, and a Cy dye as A2 (FRET=Forster resonance-energy-transfer) (cf. Fig. 1). With their widely matching spectroscopic properties (cf. Fig. 2), the combination of these dyes yielded excellent FRET efficiencies. Furthermore, fluorescence lifetime measurements revealed that the long fluorescence lifetime of the Ru complex was transferred to the Cy dye offering the possibility to measure the whole system in a time-resolved mode. The FRET system was established on double-stranded DNA (cf. Fig. 3) but it should also be generally applicable to other biomolecules.
We report on a new three-color FRET system which we were able to verify in peptides as well as in synthetic DNA. All three chromophores could be introduced by a building block approach avoiding postsynthetic labeling. Additional features are robustness, matching spectroscopic properties, high-energy transfer, and sensitivity. The system was investigated in detail on a set of peptides as well as an array of tailored oligonucleotides. The detailed analysis of the experimental data and comparison with theoretical considerations were in excellent agreement. It is shown that in the case of polypeptides specific interaction with the fluorescence probes has to be considered. In contrast with DNA, the fluorescence probes did not show any indications of such interactions. The novel three-color FRET toolbox revealed the potential for applications studying fundamental processes of three interacting molecules in life science applications.
Polymer solar cell devices with nanostructured blend layers have been fabricated using single- and dual- component polymer nanospheres. Starting from an electron-donating and an electron-accepting polyfluorene derivative, PFB and F8BT, dissolved in suitable organic solvents, dispersions of solid particles with mean diameters of ca. 50 nm, containing either the pure polymer components or a mixture of PFB and F8BT in each particle, were prepared with the miniemulsion process. Photovoltaic devices based on these particles have been studied with respect to the correlation between external quantum efficiency and layer composition. It is shown that the properties of devices containing a blend of single-component PFB and F8BT particles differ significantly from those of solar cells based on blend particles, even for the same layer composition. Various factors determining the quantum efficiency in both kinds of devices are identified and discussed, taking into account the spectroscopic properties of the particles. An external quantum efficiency of ca. 4% is measured for a device made from polymer blend nanoparticles containing PFB:F8BT at a weight ratio of 1:2 in each individual nanosphere. This is among the highest values reported so far for photovoltaic cells using this material combination
Upconversion NaYF4:Yb:Er nanoparticles co-doped with Gd3+ and Nd3+ for thermometry on the nanoscale
(2015)
In the present work, the upconversion luminescence properties of oleic acid capped NaYF4:Gd3+:Yb3+:Er3+ upconversion nanoparticles (UCNP) with pure β crystal phase and Nd3+ ions as an additional sensitizer were studied in the temperature range of 288 K < T < 328 K. The results of this study showed that the complex interplay of different mechanisms and effects, causing the special temperature behavior of the UCNP can be developed into thermometry on the nanoscale, e.g. to be applied in biological systems on a cellular level. The performance was improved by the use of Nd3+ as an additional dopant utilizing the cascade sensitization mechanism in tri-doped UCNP.
Upconversion NaYF4:Yb:Er nanoparticles co-doped with Gd3+ and Nd3+ for thermometry on the nanoscale
(2015)
In the present work, the upconversion luminescence properties of oleic acid capped NaYF4:Gd3+:Yb3+:Er3+ upconversion nanoparticles (UCNP) with pure β crystal phase and Nd3+ ions as an additional sensitizer were studied in the temperature range of 288 K < T < 328 K. The results of this study showed that the complex interplay of different mechanisms and effects, causing the special temperature behavior of the UCNP can be developed into thermometry on the nanoscale, e.g. to be applied in biological systems on a cellular level. The performance was improved by the use of Nd3+ as an additional dopant utilizing the cascade sensitization mechanism in tri-doped UCNP.
NaYF4:Yb:Er nanoparticles (UCNP) were synthesized under mild experimental conditions to obtain a pure cubic lattice. Upon annealing at different temperatures up to Tan = 700 °C phase transitions to the hexagonal phase and back to the cubic phase were induced. The UCNP materials obtained for different Tan were characterized with respect to the lattice phase using standard XRD and Raman spectroscopy as well as steady state and time resolved upconversion luminescence. The standard techniques showed that for the annealing temperature range 300 °C < Tan < 600 °C the hexagonal lattice phase was dominant. For Tan < 300 °C hardly any change in the lattice phase could be deduced, whereas for Tan > 600 °C a back transfer to the α-phase was observed. Complementarily, the luminescence upconversion properties of the annealed UCNP materials were characterized in steady state and time resolved luminescence measurements. Distinct differences in the upconversion luminescence intensity, the spectral intensity distribution and the luminescence decay kinetics were found for the cubic and hexagonal lattice phases, respectively, corroborating the results of the standard analytical techniques used. In laser power dependent measurements of the upconversion luminescence intensity it was found that the green (G1, G2) and red (R) emission of Er3+ showed different effects of Tan on the number of required photons reflecting the differences in the population routes of different energy levels involved. Furthermore, the intensity ratio of Gfull/R is highly effected by the laser power only when the β-phase is present, whereas the G1/G2 intensity ratio is only slightly effected regardless of the crystal phase. Moreover, based on different upconversion luminescence kinetics characteristics of the cubic and hexagonal phase time-resolved area normalized emission spectra (TRANES) proved to be a very sensitive tool to monitor the phase transition between cubic and hexagonal phases. Based on the TRANES analysis it was possible to resolve the lattice phase transition in more detail for 200 °C < Tan < 300 °C, which was not possible with the standard techniques.
NaYF4:Yb:Er nanoparticles (UCNP) were synthesized under mild experimental conditions to obtain a pure cubic lattice. Upon annealing at different temperatures up to Tan = 700 °C phase transitions to the hexagonal phase and back to the cubic phase were induced. The UCNP materials obtained for different Tan were characterized with respect to the lattice phase using standard XRD and Raman spectroscopy as well as steady state and time resolved upconversion luminescence. The standard techniques showed that for the annealing temperature range 300 °C < Tan < 600 °C the hexagonal lattice phase was dominant. For Tan < 300 °C hardly any change in the lattice phase could be deduced, whereas for Tan > 600 °C a back transfer to the α-phase was observed. Complementarily, the luminescence upconversion properties of the annealed UCNP materials were characterized in steady state and time resolved luminescence measurements. Distinct differences in the upconversion luminescence intensity, the spectral intensity distribution and the luminescence decay kinetics were found for the cubic and hexagonal lattice phases, respectively, corroborating the results of the standard analytical techniques used. In laser power dependent measurements of the upconversion luminescence intensity it was found that the green (G1, G2) and red (R) emission of Er3+ showed different effects of Tan on the number of required photons reflecting the differences in the population routes of different energy levels involved. Furthermore, the intensity ratio of Gfull/R is highly effected by the laser power only when the β-phase is present, whereas the G1/G2 intensity ratio is only slightly effected regardless of the crystal phase. Moreover, based on different upconversion luminescence kinetics characteristics of the cubic and hexagonal phase time-resolved area normalized emission spectra (TRANES) proved to be a very sensitive tool to monitor the phase transition between cubic and hexagonal phases. Based on the TRANES analysis it was possible to resolve the lattice phase transition in more detail for 200 °C < Tan < 300 °C, which was not possible with the standard techniques.
NaYF4:Yb:Er nanoparticles (UCNP) were synthesized under mild experimental conditions to obtain a pure cubic lattice. Upon annealing at different temperatures up to T-an = 700 degrees C phase transitions to the hexagonal phase and back to the cubic phase were induced. The UCNP materials obtained for different T-an were characterized with respect to the lattice phase using standard XRD and Raman spectroscopy as well as steady state and time resolved upconversion luminescence. The standard techniques showed that for the annealing temperature range 300 degrees C < T-an < 600 degrees C the hexagonal lattice phase was dominant. For T-an < 300 degrees C hardly any change in the lattice phase could be deduced, whereas for T-an > 600 degrees C a back transfer to the alpha-phase was observed. Complementarily, the luminescence upconversion properties of the annealed UCNP materials were characterized in steady state and time resolved luminescence measurements. Distinct differences in the upconversion luminescence intensity, the spectral intensity distribution and the luminescence decay kinetics were found for the cubic and hexagonal lattice phases, respectively, corroborating the results of the standard analytical techniques used. In laser power dependent measurements of the upconversion luminescence intensity it was found that the green (G1, G2) and red (R) emission of Er3+ showed different effects of T-an on the number of required photons reflecting the differences in the population routes of different energy levels involved. Furthermore, the intensity ratio of G(full)/R is highly effected by the laser power only when the beta-phase is present, whereas the G1/G2 intensity ratio is only slightly effected regardless of the crystal phase. Moreover, based on different upconversion luminescence kinetics characteristics of the cubic and hexagonal phase time-resolved area normalized emission spectra (TRANES) proved to be a very sensitive tool to monitor the phase transition between cubic and hexagonal phases. Based on the TRANES analysis it was possible to resolve the lattice phase transition in more detail for 200 degrees C < T-an < 300 degrees C, which was not possible with the standard techniques.