Quantification of Aldehydes on Polymeric Microbead Surfaces via Catch and Release of Reporter Chromophores

Synthesis of New Bodipy Hydrazide Fluorescent Probes for the Detection of Carbonylated Proteins Generated by Oxidative Stress

Oxidative stress is a cellular disorder implicated in various severe diseases and redox biology and represents an important field of research for the last decades. One of the major consequences of oxidative stress is the carbonylation of proteins, which is also a reliable marker to assess protein oxidative modifications. Accumulation of carbonylated proteins has been associated with aging and age-related diseases and can ultimately causes cell death. Detection of these oxidative modifications is essential to understand and discover new treatments against oxidative stress. We describe the design and the synthetic pathway of new BODIPY fluorescent probes functionalized with hydrazide function for protein carbonyl labeling to improve existing methodologies such as 2D-Oxi electrophoresis. Hydrazide BODIPY analogues show very good fluorescent properties such as NIR emission up to 633 nm and quantum yield up to 0.88. These new probes were validated for the detection and quantification of carbonylated proteins with 2D-Oxi electrophoresis using mouse muscle protein extracts, as well as both flow cytometry and microscopy using oxidant stressed C2 C12 cells.

Influence of nanoparticle encapsulation and encoding on the surface chemistry of polymer carrier beads

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.

Analyzing the surface of functional nanomaterials-how to quantify the total and derivatizable number of functional groups and ligands

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 method- and 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.

Fabrication of a "Selenium Signature" Chemical Probe-Modified Paper Substrate for Simultaneous and Efficient Determination of Biothiols by Paper Spray Mass Spectrometry

Significant efforts have been made to develop robust and reliable methods for simultaneous biothiols determination in different matrices, but there still exist the problems such as easy oxidation, tedious derivatization, and difficulty in discrimination, which brings unsatisfactory results in their accuracy and fast quantification in biological samples. To overcome these problems, a simultaneous biothiols detection method combining a "selenium signature" chemical probe and paper spray mass spectrometry (PS-MS) was proposed. In the strategy, the modified-paper substrate is used to enhance the analytical performance. Chemical probe Ebselen-NH₂ that has a specific response to biothiols was designed and covalently fixed on the surface of an oxidized paper substrate. By the identification of derivatized product with distinctive selenium isotope distribution and employment of the optimized PS-MS method, qualitative and quantitative analysis of five biothiols including glutathione (GSH), cysteine (Cys), cysteinylglycine (CysGly), N-acetylcysteine (Nac), and homocysteine (Hcy) were realized. Biothiols in plasma and cell lysates were measured with satisfactory results. The established method not only provides a novel protocol for simultaneous determination of biothiols, but also is helpful for understanding the biological and clinical roles played by these bioactive small molecules.

Capture and Release of Protein-Nanoparticle Conjugates by Reversible Covalent Molecular Linkers

A hybrid approach to covalently detachable molecules for nanoparticle capture and release from several custom-functionalized surfaces is described. This new surface chemistry capability provides a means for reversible binding of functionalized nanoparticles without relying on costly nucleic acid-based complexation. A new surface linker motif was devised wherein custom molecules were synthesized with components for surface anchoring, cleavage, and target capture through biotin-streptavidin binding. All capture-and-release chemistry is performed using physiological conditions (aqueous, pH 7). Covalent cleavage of linker molecules was achieved through incorporation of a tunable orthogonal reversible covalent (TORC) hydrazone functional group which underwent exchange with a competitive hydrazide aided by an aniline catalyst. The influence of the linker architecture on hydrazone exchange and nanoparticle release was probed by altering the distance between hydrazone and biotin groups using different length PEG spacers. Cleavable linkers were used to functionalize microwells, magnetic separation beads, and gold-coated glass surfaces. Upon functionalization, all surface types bound streptavidin and conjugated nanoparticles regardless of the linker structure. Conversely, the extent of hydrazone exchange as well as release of nanoparticles were influenced both by the hydrazone surface density and the linker molecular structure.