Colorimetric quantification of amino groups in linear and dendritic structures

Size-based characterization of dendrigraft poly(L-lysine) by free solution capillary electrophoresis using polyelectrolyte multilayer coatings

Dendrigraft poly(L-lysine) (DGL) constitutes a promising dendritic-like drug vehicle with high biocompatibility and straightforward access via ring-opening polymerization of N-carboxyanhydride in water. The characterization of the different generations of DGL is however challenging due to their heterogeneity in molar mass and branching ratio. In this work, free solution capillary electrophoresis was used to perform selective separation of the three first generations of DGL, and optimized conditions were developed to maximize inter-generation resolution. To reduce solute adsorption on the capillary wall, successive multiple ionic polymer layer coatings terminated with a polycation were deposited onto the inner wall surface. PEGylated polycation was also used as the last layer for the control of the electroosmotic flow (EOF), depending on the PEGylation degree and the methyl-polyethylene glycol (mPEG) chain length. 1 kDa mPEG chains and low grafting densities were found to be the best experimental conditions for a fine tuning of the EOF leading to high peak resolution. Molar mass polydispersity and polydispersity in effective electrophoretic mobility were successfully determined for the three first generations of DGL.

Versatile lysine dendrigrafts and polyethylene glycol hydrogels with inherent biological properties: in vitro cell behavior modulation and in vivo biocompatibility

Poly(ethylene glycol) (PEG) hydrogels have been extensively used as scaffolds for tissue engineering applications, owing to their biocompatibility, chemical versatility, and tunable mechanical properties. However, their bio-inert properties require them to be associated with additional functional moieties to interact with cells. To circumvent this need, we propose here to reticulate PEG molecules with poly(L-lysine) dendrigrafts (DGL) to provide intrinsic cell functionalities to PEG-based hydrogels. The physico-chemical characteristics of the resulting hydrogels were studied in regard of the concentration of each component. With increasing amounts of DGL, the cross-linking time and swelling ratio could be decreased, conversely to mechanical properties, which could be tailored from 7.7 ± 0.7 to 90 ± 28.8 kPa. Furthermore, fibroblasts adhesion, viability, and morphology on hydrogels were then assessed. While cell adhesion significantly increased with the concentration of DGL, cell viability was dependant of the ratio of DGL and PEG. Cell morphology and proliferation; however, appeared mainly related to the overall hydrogel rigidity. To allow cell infiltration and cell growth in 3D, the hydrogels were rendered porous. The biocompatibility of resulting hydrogels of different compositions and porosities was evaluated by 3 week subcutaneous implantations in mice. Hydrogels allowed an extensive cellular infiltration with a mild foreign body reaction, histological evidence of hydrogel degradation, and neovascularization.

Plasma Polymer Coatings To Direct the Differentiation of Mouse Kidney-Derived Stem Cells into Podocyte and Proximal Tubule-like Cells

Kidney disease is now recognized as a global health problem and is associated with increased morbidity and mortality, along with high economic costs. To develop new treatments for ameliorating kidney injury and preventing disease progression, there is a need for appropriate renal culture systems for screening novel drugs and investigating the cellular mechanisms underlying renal pathogenesis. There is a need for in vitro culture systems that promote the growth and differentiation of specialized renal cell types. In this work, we have used plasma polymerization technology to generate gradients of chemical functional groups to explore whether specific concentrations of these functional groups can direct the differentiation of mouse kidney-derived stem cells into specialized renal cell types. We found that amine-rich (-NH₂) allylamine-based plasma-polymerized coatings could promote differentiation into podocyte-like cells, whereas methyl-rich (CH₃) 1,7-octadiene-based coatings promoted differentiation into proximal tubule-like cells (PTC). Importantly, the PT-like cells generated on the substrates expressed the marker megalin and were able to endocytose albumin, indicating that the cells were functional.

Everything You Always Wanted to Know about Poly-l-lysine Dendrigrafts (But Were Afraid to Ask)

Less than a decade ago, dendrigrafts of poly-l-lysine (DGLs) joined the family of polycationic dendritic macromolecules. Resulting from the iterative polycondensation of an N-carboxyanhydride in water, four generations of the dendrigraft can be obtained on a multigram scale and without chromatographic purification. DGLs share features with both dendrimers and hyperbranched polymers, but turned out to have unique biophysical and bioactive properties. The macromolecules-in their native form or functionalized-have been extensively characterized by various analytical and computational methods, and have already found numerous applications in the biomedical field, such as drug and gene delivery, biomaterials, tissue engineering, bioimaging, and biosensing. Despite a growing interest for DGLs, there is still plenty of room for further exciting developments that could result from a better exposure of these macromolecules, which is the ambition of this short review.

Folate-modified silicon carbide nanoparticles as multiphoton imaging nanoprobes for cancer-cell-specific labeling

SHG-active SiC nanoparticles were modified with folic acid for cancer-cell-specific labelling.

Characterization of three amino-functionalized surfaces and evaluation of antibody immobilization for the multiplex detection of tumor markers involved in colorectal cancer

Antibody microarrays are powerful and high-throughput tools for screening and identifying tumor markers from small sample volumes of only a few microliters. Optimization of surface chemistry and spotting conditions are crucial parameters to enhance antibodies' immobilization efficiency and to maintain their biological activity. Here, we report the implementation of an antibody microarray for the detection of tumor markers involved in colorectal cancer. Three-dimensional microstructured glass slides were functionalized with three different aminated molecules ((3-aminopropyl)dimethylethoxysilane (APDMES), Jeffamine, and chitosan) varying in their chain length, their amine density, and their hydrophilic/hydrophobic balance. The physicochemical properties of the resulting surfaces were characterized. Antibody immobilization efficiency through physical interaction was studied as a function of surface properties as well as a function of the immobilization conditions. The results show that surface energy, steric hindrance, and pH of spotting buffer have great effects on protein immobilization. Under optimal conditions, biological activities of four immobilized antitumor marker antibodies were evaluated in multiplex immunoassay for the detection of the corresponding tumor markers. Results indicated that the chitosan functionalized surface displayed the highest binding capacity and allowed to retain maximal biological activity of the four tested antibody/antigen systems. Thus, we successfully demonstrated the application of amino-based surface modification for antibody microarrays to efficiently detect tumor markers.

Interpretation of protein quantitation using the Bradford assay: comparison with two calculation models

The Bradford assay is a simple method for protein quantitation, but variation in the results between proteins is a matter of concern. In this study, we compared and normalized quantitative values from two models for protein quantitation, where the residues in the protein that bind to anionic Coomassie Brilliant Blue G-250 comprise either Arg and Lys (Method 1, M1) or Arg, Lys, and His (Method 2, M2). Use of the M2 model yielded much more consistent quantitation values compared with use of the M1 model, which exhibited marked overestimations against protein standards.

PREPARATION OF CORE-SHELL SILVER/SILICA NANOPATICLES AND THEIR APPLICATION FOR ENHANCEMENT OF CYANINE 3 FLUORESCENCE

Core shell Ag@SiO2 -Streptavidin- Cy3 nanoparticles were prepared. Ag@SiO2 nanoparticles were synthesized via a sol–gel method. Then, Streptavidin- Cy3 was covalently bonded to the Ag@SiO2 surface. These core-shell nanoparticles were characterized by steady-state fluorescence spectroscopy and fluorescence scanning. In presence of the silver core, a 2.5-time enhancement of Cy3 fluorescence intensity was obtained. This result shows that these nanoparticles can be potentially helpful in surface analysis based on biochip.

Purification of Coomassie Brilliant Blue G-250 by multiple dual mode countercurrent chromatography

Commercial samples of Coomassie Brilliant Blue G-250 (CBB) were not pure enough to give reliable results when used as indicator of amine content in biological material. The polar and apolar impurities produce unacceptable biases in the results. Counter current chromatography (CCC) was used to purify significant amounts of CBB. The liquid system heptane/1-butanol/water 2:3:4 (v/v) was appropriate to separate crude CBB in three groups of components: polar, partitioning in the aqueous lower phase, intermediate, partitioning well between the aqueous and organic phases, and apolar, preferring greatly the organic phase. The dual-mode way of using a CCC chromatograph was found appropriate for the separation injecting the crude CBB in the middle of a two coil CCC instrument. A multi dual-mode purification was performed allowing to eliminate the polar impurities in the aqueous phase at the column tail and the apolar ones in the organic phase at the column head, trapping the purified dye inside the CCC column. 200mg of purified CBB were obtained from 1g of crude CBB in 3h using as little as 150 mL of butanol and 70 mL of heptane with 200 mL of water. The purified CBB gave total satisfaction in testing amine content in polyclonal antibody containing monolith pipettes.

Preparation and full characterization of a micro-immunoaffinity monolithic column and its in-line coupling with capillary zone electrophoresis with Ochratoxin A as model solute

A micro-immunoaffinity monolithic column (μIAC) was developed and in-line coupled with capillary zone electrophoresis in a fully automated way with Ochratoxin A as test solute. The in-line micro-immunoaffinity columns based on monolithic methacrylate polymers (EDMA-GMA) were prepared in situ at the inlet end of a PTFE coated fused silica capillary by UV initiated polymerization and subsequently grafted with antibodies. These μIACs were thoroughly characterized. The synthesis of the polymeric support was first demonstrated to be reproducible in terms of permeability, surface properties and efficiency. The antibodies immobilization was then studied by a new original hydrodynamic method (ADECA) allowing the in situ quantitative determination (at a miniaturized scale) of the total amount of immobilized antibodies. The combination of this measurement with the binding capacity of the μIAC allowed, for the first time, the in situ determination of immobilized antibody activity. A total of 260 ± 15 ng (1.6 ± 0.1 pmol) of IgG antibodies/cm in 75 μm i.d. monolithic column (i.e. 18 μgmg(-1)) was obtained with (anti-Ochratoxin A/Ochratoxin A) as antibody/antigen model. 40% of the immobilized antibodies remain active corresponding to a binding capacity of 1.2 ± 0.2 pmol antigen/cm (i.e. 600 pg/cm of our test solute OTA), a very high capacity when dealing with trace analysis and with regard to the detection limits (30 pg and 0.5 pg with UV and LIF detection, respectively). The recovery yields were quantitative with negligible non-specific adsorption and allow analysis of diluted samples (1 ngmL(-1)) for a percolated volume of 10 μL. It was also demonstrated that despite the progressive denaturation of antibodies consecutive to the elution step, the binding capacity of the μIAC remained high enough to implement at least 15 consecutive analyses with the same column and in a fully automated way.

Quantification of primary amine groups available for subsequent biofunctionalization of polymer surfaces

Biocompatible polymers are commonly functionalized with specific moieties such as amino groups to modify their surface properties and/or to attach bioactive compounds. A reliable method is usually required to characterize amino group surface densities. In this study, aminated polyethylene terephthalate (PET) films were generated via an aminolysis reaction involving either ethylenediamine molecules (EtDA), in order to vary easily the amino group density on PET surfaces, or 25 kDa polyvinylamine (PVAm) as an alternative reagent preventing bulk damages resulting from the aminolysis reaction. Among commonly used dyes for amino group quantification, Orange II and Coomassie Brillant Blue (CBB) were selected to quantify the extent of amine grafting resulting from these derivatization procedures. Rapid and convenient colorimetric assays were compared to surface atomic compositions obtained from X-ray photoelectron spectroscopy (XPS) measurements. Orange II was found to be the most appropriate dye for quantifying primary amine groups in a reliable and specific way. Due to its unique negative charge and low steric hindrance compared to CBB, the Orange II dye was very sensitive and provided reliable quantification over a wide range of amino group surface densities (ca. 5 to at least 200 pmol/mm(2)). In order to further validate the use of the Orange II dye for amino group quantification, a heterobifunctional linker reacting with amino groups was then grafted on modified PET surfaces. Interestingly, the good correlation between the densities of adsorbed Orange II and covalently grafted linkers suggests that the Orange II method is a relevant, reliable, easy, and inexpensive method to predict the amount of amino groups available for subsequent functionalization of polymer surfaces.