Filtern
Dokumenttyp
- Zeitschriftenartikel (7)
- Vortrag (6)
- Posterpräsentation (5)
- Sonstiges (1)
Sprache
- Englisch (19)
Schlagworte
- Fluorescence (11)
- Polymerization (8)
- Nano (7)
- Microbeads (6)
- Particle (6)
- Quality assurance (6)
- Surface chemistry (6)
- Quantum dots (5)
- Luminescence (4)
- Method (4)
Organisationseinheit der BAM
Paper des Monats
- ja (1)
The growth of ultrathin layers of VOx (<12 monolayers) on Pt(111) and the activity of these layers in catalytic methanol oxidation at 10−4 mbar have been studied with low-energy electron difraction, Auger electron spectroscopy, rate measurements, and with photoemission electron microscopy. Reactive deposition of V in O2 at 670 K obeys a Stranski–Krastanov growth mode with a (√3 × √3)R30° structure representing the limiting case for epitaxial growth of 3D-VOx. The activity of VOx/Pt(111) in catalytic methanol oxidation is very low and no redistribution dynamics is observed lifting the initial spatial homogeneity of the VOx layer. Under reaction conditions, part of the surface vanadium difuses into the Pt subsurface region.
Exposure to O2 causes part of the V to difuse back to the surface, but only up to one monolayer of VOx can be stabilized in this way at 10−4 mbar.
Functional nanomaterials (NM) of different size, shape, chemical composition, and surface chemistry are of increasing relevance for many key technologies of the twenty-first century. This includes polymer and silica or silica-coated nanoparticles (NP) with covalently bound surface groups, semiconductor quantum dots (QD), metal and metal oxide NP, and lanthanide-based NP with coordinatively or electrostatically bound ligands, as well as surface-coated nanostructures like micellar encapsulated NP. The surface chemistry can significantly affect the physicochemical properties of NM, their charge, their processability and performance, as well as their impact on human health and the environment. Thus, analytical methods for the characterization of NM surface chemistry regarding chemical identification, quantification, and accessibility of functional groups (FG) and surface ligands bearing such FG are of increasing importance for quality control of NM synthesis up to nanosafety. Here, we provide an overview of analytical methods for FG analysis and quantification with special emphasis on bioanalytically relevant FG broadly utilized for the covalent attachment of biomolecules like proteins, peptides, and oligonucleotides and address methodand material-related challenges and limitations. Analytical techniques reviewed include electrochemical titration methods, optical assays, nuclear magnetic resonance and vibrational spectroscopy, as well as X-ray based and thermal analysis methods, covering the last 5–10 years. Criteria for method classification and evaluation include the need for a signal-generating label, provision of either the total or derivatizable number of FG, need for expensive instrumentation, and suitability for process and production control during NM synthesis and functionalization.
Surface-functionalized polymer beads encoded with molecular luminophores and nanocrystalline emitters such as semiconductor nanocrystals, often referred to as quantum dots (QDs), or magnetic nanoparticles are broadly used in the life sciences as reporters and carrier beads. Many of these applications require a profound knowledge of the chemical nature and total number of their surface functional groups (FGs), that control bead charge, colloidal stability, hydrophobicity, and the interaction with the environment and biological systems. For bioanalytical applications, also the number of groups accessible for the subsequent functionalization with, e.g., biomolecules or targeting ligands is relevant. In this study, we explore the influence of QD encoding on the amount of carboxylic acid (COOH) surface FGs of 2 μm polystyrene microparticles (PSMPs). This is done for frequently employed oleic acid and oleylamine stabilized, luminescent core/shell CdSe QDs and two commonly used encoding procedures. This included QD addition during bead formation by a thermally induced polymerization reaction and a post synthetic swelling procedure. The accessible number of COOH groups on the surface of QD-encoded and pristine beads was quantified by two colorimetric assays, utilizing differently sized reporters and electrostatic and covalent interactions. The results were compared to the total number of FGs obtained by a conductometric titration and Fourier transform infrared spectroscopy (FTIR). In addition, a comparison of the impact of QD and dye encoding on the bead surface chemistry was performed. Our results demonstrate the influence of QD encoding and the QD-encoding strategy on the number of surface FG that is ascribed to an interaction of the QDs with the carboxylic acid groups on the bead surface. These findings are of considerable relevance for applications of nanoparticle-encoded beads and safe-by-design concepts for nanomaterials.
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, Semiconductor Nanoparticle-loaded Polymer Microbeads - Comparing Particle Architectures
(2024)
The synthesis of luminescent polymer microparticles stained with different, including non-spherical, semiconductor nanoparticles (NPs) was developed and optimized while ensuring a good preservation of the particle photoluminescence. The aplicability of the different semiconductor NPs was determined to depend on their surface chemistry and shape. Thus, a first correlation of semiconductor NP architecture and applicability could be deduced, which has not been reported before.
Luminescent polymer microbeads are applied in bead-based platforms for biomolecule binding interactions, and the encoding of these beads is important for the realization of optically distinguishable barcodes. While dye- encoded beads often suffer from photobleaching and spectral crosstalk due to the relatively broad dye emission band, quantum dot (QD)-encoded beads absorb in a very broad wavelength range and reveal narrow emission bands, which enables simultaneous excitation of beads stained with differently colored QDs. To address existing limitations of QD encoding, we have explored simple and effective approaches to homogeneously stain polymer particles and identify suitable polymerization reactions and QD surface ligands that tackle these challenges.
Luminescent, Semiconductor Nanoparticle-Loadedpolymer Microbeads–Comparingparticlearchitectures
(2025)
Luminescent polymer microparticles (PMPs) are applied in various (bio)analytical and diagnostic processes.[1] The staining of these beads is important for the realization of optically distinguishable barcodes that can be read out, e.g., by a flow cytometer or fluorescence microscope. Typically, luminescent semiconductor nanoparticles (NPs) absorb in a broad wavelength range and show narrow emission bands, which enables simultaneous excitation of differently colored luminophores and facilitates a spectral discrimination.[1] This makes them ideal candidates for this purpose and encouraged us to explore and develop a simple, effective approach to luminescent semiconductor NP encoding of polystyrene PMPs and identify suitable synthesis conditions.[2]
Until now, mainly semiconductor quantum dots (QDs) have been used for the synthesis of luminescent PMPs, although NPs with different shapes could introduce beneficial new features. Aiming for the application of our developed procedure to non-spherical NPs, we systematically investigated the luminescence properties of the resulting NP-stained beads using fluorescence and integrating sphere spectroscopy as well as fluorescence and electron microscopy. These studies showed that the suitability of semiconductor NPs for the synthesis of luminescent PMPs depends not only on their shape, but also heavily on their surface chemistry.[3] The successful incorporation of nonspherical NPs opens the path to include even more NPs, and the results can help to deduce future applications for the beads which best suit their specific properties.
Ratiometric green–red fluorescent nanosensors for fluorometrically monitoring pH in the acidic range were designed from 80 nm-sized polystyrene (PS) and silica (SiO2) nanoparticles (NPs), red emissive reference dyes, and a green emissive naphthalimide pH probe, analytically and spectroscopically characterized, and compared regarding their sensing performance in aqueous dispersion and in cellular uptake studies. Preparation of these optical probes, which are excitable by 405 nm laser or LED light sources, involved the encapsulation of the pH-inert red-fuorescent dye Nile Red (NR) in the core of self-made carboxylated PSNPs by a simple swelling procedure and the fabrication of rhodamine B (RhB)-stained SiO2-NPs from a silane derivative of pH-insensitive RhB. Subsequently, the custom-made naphthalimide pH probe, that utilizes a protonation-controlled photoinduced electron transfer process, was covalently attached to the carboxylic acid groups at the surface of both types of NPs. Fluorescence microscopy studies with the molecular and nanoscale optical probes and A549 lung cancer cells confirmed the cellular uptake of all probes and their penetration into acidic cell compartments, i.e., the lysosomes, indicated by the switching ON of the green naphthalimide fluorescence. This underlines their suitability for intracellular pH sensing, with the SiO2-based nanosensor revealing the best performance regarding uptake speed and stability.
