Surface Amine Density Research Articles

Use of Ball Drop Casting and Surface Modification for the Development of Amine-Functionalized Silica Aerogel Globules for Dynamic and Efficient Direct Air Capture.

Amine-functionalized silica aerogel globules (AFSAGs) were first synthesized via a simple ball drop casting method followed by amine grafting. The effect of grafting time on the structure and CO2 adsorption performance of the AFSAGs was investigated. The CO2 adsorption performance was comprehensively studied by breakthrough curves, adsorption capacity and rates, surface amine loading and density, amine efficiency, adsorption halftime, and cyclic stability. The results demonstrate that prolonging the grafting time does not lead to a significant increase in surface amine content owing to pore space blockage by superabundant amine groups. The CO2 adsorption performance shows obvious dependence on surface amine density, determined by both the surface amine content and specific surface area, and working temperature. AFSAGs with a grafting time of 24 h (AFSAG24) with a moderate surface amine density have optimal CO2 adsorption capacities, which are 1.78 and 2.14 mmol/g at 25 °C with dry and humid 400 ppm CO2, respectively. The amine efficiency of AFSAG24 with low CO2 concentrations, 0.38-0.63 with dry 400 ppm-1% CO2, is the highest among the reported amine-functionalized adsorbents. After estimation with different diffusion models, the CO2 adsorption process of AFSAG24 is governed by film diffusion and intraparticle diffusion. In the range of 1-4 mm, the ball size does not affect the CO2 adsorption capacity of AFSAG24 obviously. AFSAG24 offers significant advantages for practical direct air capture compared with its state-of-the-art counterparts, such as high dynamic adsorption capacity and amine efficiency, excellent stability, and outstanding adaptation to the environment.

One-step fabrication method of non-fouling amine-functionalized polyethylene glycol thin film using a single precursor through plasma-enhanced chemical vapor deposition

Fabrication methods to produce an amine-functionalized surface have been widely investigated as it is a promising substrate for biological studies, owing to its ability to stably immobilize various biomolecules. In this study, a biocompatible amine-functionalized polyethylene glycol (aPEG) thin film was fabricated by using plasma-enhanced chemical vapor deposition (PECVD) to overcome the disadvantages of the conventional wet process. A functionalized PEG diamine was used as a single precursor to simplify the fabrication process, and the relationship between the surface functional group density and the plasma power was investigated. Also, the surfaces of the functionalized thin films were quantitatively analyzed to determine the optimal fabrication condition that yields the most excellent surface amine density. The non-fouling resistance of the aPEG thin film and its applicability for biological applications was demonstrated by successfully immobilizing the matrix metalloproteinase-7 (MMP-7) enzyme, which is a well-known biomarker for cancers, with minimal non-specific adsorption (NSA). Our fabrication method was further applied to the modification of rather challenging substrates, including carbon paper, polyethylene terephthalate (PET) film, silicon wafer, polyvinylidene fluoride (PVDF), and successful modification was confirmed by the results of time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis. It is expected that our fabrication method can enable applications of the functionalized thin film in bioscience by presenting a versatile surface modification technique for deposition of biocompatible material onto various substrates, which can be potentially used in disease diagnosis, medical implants, and bioengineering.

Plasma-polymerized antifouling biochips for label-free measurement of protease activity in cell culture media

We report polyethylene glycol (PEG)-grafting antifouling surfaces using a plasma copolymerized (PcP) technique to monitor protease activity in complex media. By varying the mixing ratio of the PEG and ethylenediamine (EDA) precursors, the PcP-PEG-EDA (PcP-PE) film was able to easily control surface amine density with good preservation of the internal PEG structure. We found that nonspecific protein adsorption was dramatically reduced in serum-containing media on the PcP-PE films, as opposed to that on plasma polymerized-EDA (PP-E) films without PEG. When SPR sensor chips coated with PcP-PE film were employed to detect protease activity, biotinylated luciferase probes (luciferase-peptide-biotin) on streptavidin-conjugated SPR chips enabled real-time and label-free measurement of matrix metalloproteinase activity in cell culture media. Owing to its excellent antifouling ability, this newly developed method boasts minimal nonspecific binding and can serve as a biochip platform to promote a wide range of applications in the biological field.

CO2 capture using triamine-grafted SBA-15: The impact of the support pore structure

The impact of the support pore structure on the CO2 adsorption performance of triamine-tethered SBA-15 silica was studied. Six SBA-15 silica supports with different pore sizes and intrawall pore volumes were synthesized, followed by triamine functionalization through dry and wet grafting (i.e., with and without added water). CO2 adsorption measurements showed the positive impact of support large pore size and high intrawall pore volume on adsorptive properties, with the former being dominant. Large-pore supports exhibited the highest surface density of amine groups (up to 35 μmol/m2), highest CO2 uptakes (up to 1.88 mmol CO2/g) and CO2/N ratios (up to 0.33 mol CO2/mol N), and fastest adsorption kinetics. When the intrawall pore volume decreased by 53% for samples with identical pore sizes, lower CO2 uptakes (up to 63%) and CO2/N ratios (up to 62%), and slower adsorption kinetics were observed, particularly for the lowest adsorption temperature (i.e., 25 °C). It was inferred that large pore size and/or high intrawall pore volume of the support improve the adsorptive properties via enhanced amine accessibility. Large-pore supports also allowed higher surface amine density to be achieved because of reduced steric hindrance between grafted triamine species.

Ratiometric fluorescent response of electrospun fibrous strips for real-time sensing of alkaline phosphatase in serum

The development of rapid, convenient and reliable assays for monitoring alkaline phosphatase (ALP) levels is valuable for clinical diagnoses and biomedical research. In the current study, a ratiometric assay of ALP activity has been realized by covalent immobilization of fluorescein onto polyethylene terephthalate (PET) fibers, followed by electrostatic adsorption of bisquaternary ammonium salt of tetraphenylethene (TPE-2N+). In the absence of ALP, the complex formation between phosphorylated fluorescein and TPE-2N+ results in the aggregation-induced emission (AIE) of TPE at 471nm. While in the presence of ALP, the hydrolysis of phosphoesters leads to a gradual removal of TPE-2N+ and the restoration of fluorescein emission at 514nm. Fibers with surface amine densities of 30 nmol/mg show the most significant and almost linear increases in I514/I471 ratios from 0.73 to 3.05 with increasing ALP concentrations from 0 to 100 mU/mL. The ratiometric fluorescence responses result in color changes of fibrous strips from blue (TPE-2N+) to green (fluorescein) under an ultraviolet lamp in a matter of minutes. The color changes are more suitable for an eyeball detection of ALP levels ranging from 0 to 80 mU/mL, which is included in the concentration range of ALP in human serum considering the dilution factor if necessary. The ALP detection indicates no apparent interference by serum components and good agreement with enzyme-linked immunosorbent assay (ELISA). Thus, this is the first study on ratiometric fluorescent assay of serum ALP levels by fibrous strips, which offers a capacity to exploit electrospun fibrous mats and ratiometric responses for real-time assays of bioactive substances as self-test devices.

Surface functionalization of silica particles for their efficient fluorescence and stereo selective modification

Abstract Optimization of reaction conditions between surface silanols of silica particles and 3-aminopropyltriethoxysilane is performed. A reasonably good surface coverage by amino groups is achieved by adjustment of solvent polarity, temperature and reaction time. The best results are obtained for the ratio of toluene/ethanol 9:1 (v/v) and 5 h of reaction time at 50 °C, which can be further improved increasing the surface amine density from 0.62 to 0.87 groups/nm 2 under dry silanization conditions. The availability of surface amino groups for further coupling is verified by decoration of anisotropically modified (Janus) particles with gold nanoparticles and by reaction with a fluorescent dye Rhodamine B isothiocyanate. The duration of coupling with the dye is crucial for efficient dye incorporation and particle fluorescence. The emission intensity of the dyed particles declines if the reaction is conducted for more than 24 h because of the degradation of the particle-dye adduct.

Stepwise Orthogonal Click Chemistry toward Fabrication of Paclitaxel/Galactose Functionalized Fluorescent Nanoparticles for HepG2 Cell Targeting and Delivery

In this report, we used stepwise orthogonal click chemistry (SOCC) involving strain-promoted azide-alkyne cycloaddition (SPAAC) and microwave-assisted Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) to assemble an anticancer drug (paclitaxel, PTX) and a targeting ligand (trivalent galactoside, TGal) on a fluorescent silicon oxide nanoparticle (NP) by using dialkyne linker 8 as a bridge. The fluorescent NH2@Cy3SiO2NP was fabricated using a competition method to incorporate Cy3 without loss of the original surface amine density on the NPs. The concept of SOCC was first investigated in a solution-phase model study that showed quantitative reaction yield. In the fabrication of TGal-PTX@Cy3SiO2NP, the expensive compound azido-functionalized PTX 12 used in SPAAC can be easily recovered due to the absence of other reagents in the reaction mixture. High loading of the sugar ligand on the NP surface serves a targeting function and also overcomes the low water solubility of PTX. Confocal fluorescence microscopy and cytotoxicity assay showed that TGal-PTX@Cy3SiO2NP was taken up by HepG2 cells and was affected by the microtubule skeleton in these cells and inhibited the proliferation of these cells in a dose-dependent manner. The presence of a fluorescent probe, a targeting ligand, and an anticancer drug on the multifunctional TGal-PTX@Cy3SiO2NP allows for real-time imaging, specific cancer-cell targeting, and the cell-killing effect which is better than free PTX.

Grafting of Amines on Ethanol-Extracted SBA-15 for CO2 Adsorption.

SBA-15 prepared via ethanol extraction for template removing was grafted with three kinds of amine precursors (mono-, di-, tri-aminosilanes) to synthesis new CO2 adsorbents. The SBA-15 support and the obtained adsorbents were characterized by X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), N2 adsorption/desorption, thermogravimetry (TG), elemental analysis, Fourier transform infrared (FTIR) spectrometry, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that, except higher silanol density, the ethanol-extracted SBA-15 support possessed a more regular mesophase and thicker walls than traditionally calcined samples, leading to a good stability of the adsorbent under steam treatment. The adsorption capacity of different amine-grafted samples was found to be influenced by not only the surface amine density, but also their physiochemical properties. These observations provide important support for further studies of applying amine-grafted adsorbents in practical CO2 capture process.

The effect of nanofibre surface amine density and conjugate structure on the adhesion and proliferation of human haematopoietic progenitor cells

Previous studies have shown that substrate surface chemistry and topography exhibit significant impact on haematopoietic progenitor cell adhesion, proliferation and differentiation. In the present study, the effect of surface amine density and structure of grafted polymer chains on the adhesion and expansion of haematopoietic progenitor cells was investigated. Cryopreserved human umbilical cord blood CD133(+) cells were expanded in cytokine-supplemented medium on ethylenediamine (EDA)- or 2-aminoethyl methacrylate hydrochloride (AEMA)-grafted polyethersulphone (PES) nanofibre scaffolds for 10 days. Although the percentage of CD34(+) cells among the expanded cells increased with the surface amine density, the maximum fold expansion of CD34(+) cells was obtained at a moderate amine density of 20-80 nmol cm(-2). When comparing nanofibre matrices with similar amine densities, but prepared with two different methods, cells cultured on the AEMA-grafted PES nanofibre matrix showed lower fold expansion in terms of total cell number (300 ± 84 fold) and CD34(+) cell number (68 ± 19-fold) in comparison with those cultured on EDA-grafted nanofibres (787 ± 84-fold and 185 ± 84-fold, respectively). These results indicate that the surface amine density and the conjugate structure are important determinants for the preservation of CD34 surface marker and expansion efficiency of CD34(+) cells.

Nanoengineering life: from cell to tissue

Nanoengineering, which brings several traditional disciplines including physics, engineering, biology and medicine together, is an emerging tool for manipulating major constituents of living organisms such as cells and tissues. Generally, the scopes of nanoengineering techniques include

Surface functionalisation of magnetic nanoparticles: quantification of surface to bulk amine density

Work has been conducted to adapt a colourimetric assay previously used on flat surfaces for the assay of amine group density on nanoparticles silanised with 3-(aminopropyl) triethoxysilane. The new assay was rapid, easy to perform, and linear in the range of optical density (OD282 nm) values of 0.080–1.6 for particle suspension densities of between 0.5 and 7.0 mg/ml. In addition, the same materials, as well as the ones activated using 3-(aminopropyl) diethoxy methyl silane, were investigated for their elemental compositions by, combustion carbon-hydrogen-nitrogen (CHN) analysis and results from both approaches together have permitted the accurate calculation of the ratio of surface to total amine density for the materials when activated in water. This value can in turn be used as an indication of a surface amino structure (i.e. mono or multilayer). The aminosilanisation processes were further characterised by DNA-binding/elution and zeta potential measurement. This combination of approaches provides a fast, convenient and effective means of measuring surface amine densities on particles and yields information about the structure of the surface aminosilanes layers.

One-pot green synthesis of biocompatible arginine-stabilized magnetic nanoparticles

A green one-step approach has been developed for the synthesis of amino-functionalizedmagnetite nanoparticles. The synthesis was accomplished by simply mixingFeCl2 with arginine under ambient conditions. It was found that theFe2+/arginine molar ratio, reaction duration and temperature greatly influence the size, morphologyand composition of magnetic nanoparticles. The arginine-stabilized magneticnanoparticles were characterized by transmission electron microscopy, x-ray diffraction,x-ray photoelectron spectroscopy, thermogravimetric analysis, and Fouriertransform infrared spectroscopy techniques. The results show that the preparednanoparticles are spherically shaped with a nearly uniform size distribution andpure magnetite phase. The presence of arginine on the magnetic nanoparticlesurface has been confirmed and the amount of surface arginine varies with theFe2+/arginine molar ratio. The surface amine densities are calculated to be 5.60 and 7.84 µmol mg−1 for magnetic nanoparticles prepared at 1:1 and 1:2Fe2+/arginine molar ratio, respectively. The as-synthesized nanoparticles show superparamagneticbehavior at room temperature and good solubility in water. In addition, using a similarsynthesis procedure, we have been able to synthesize superparamagnetic manganese andcobalt ferrite nanoparticles.

Preparation of γ-APS monolayer with complete coverage via contact printing

A monolayer film of 3-aminopropyltriethoxysilane (γ-APS) was prepared by contact printing with featureless PDMS stamp. First, γ-APS ink solutions in dry toluene were prepared in a dry nitrogen-filled glove box and immediately used for spin coating onto a PDMS stamp, followed by printing on a silicon wafer. Next, water contact angles and film thicknesses were measured as a function of ink concentration (5–100 mM) and printing time (1–60 min) after printing, as well as after aging in toluene for 24 h. In addition, surface coverage, topology, RMS roughness and surface amine density were also evaluated, while the chemical structure of γ-APS monolayer was analyzed by FT-IR/ATR. Optimum conditions for γ-APS monolayer with complete coverage were determined to be ink concentration of 20 mM and printing time of 30 min, which resulted in a water contact angle of 93°, film thickness of 0.78 nm and surface amine density of 7.6 molecules/nm 2.

Inducing Efficient Cross-priming Using Antigen-coated Yeast Particles

Saccharomyces cerevisiae stimulates dendritic cells (DCs) and represents a promising candidate for cancer vaccine development. Effective cross-presentation of antigen delivered to DCs is necessary for successful induction of cellular immunity. Here, we present a yeast-based vaccine approach that is independent of yeast's ability to express the chosen antigen, which is instead produced separately and conjugated to the yeast cell wall. The conjugation method is site-specific (based on the SNAP-tag) and designed to facilitate antigen release in the DC phagosome and subsequent translocation for cross-presentation. We demonstrate that nonsite-specific chemical conjugation of the same protein hinders cross-presentation. Phagosomal antigen release was further expedited through the insertion of the invariant chain ectodomain as a linker, which is rapidly cleaved by Cathepsin S. The dose of delivered antigen was increased in several ways: by using yeast strains with higher surface amine densities, by using yeast hulls (cell wall fragments) instead of whole cells, and by conjugating multiple layers of antigen. The novel multilayer conjugation scheme takes advantage of Sfp phosphopantetheinyl transferase and remains site-specific; it enables the antigen dose to grow linearly with the number of layers. We show that whole yeast cells coated with 1 layer of the cancer-testis antigen NY-ESO-1 and yeast hulls bearing 3 layers were able to cross-prime naive CD8 T cells in vitro, with the latter resulting in higher frequencies of antigen-specific cells after 10 days. This cross-presentation-efficient antigen conjugation scheme is not limited to yeast and can readily be applied toward the development of other particulate vaccines.

Surface Modification via Plasma Polymerization of Allylamine for Antibody Immobilization

AbstractContinuous wave and pulsed plasma polymerization coatings of allylamine were investigated for antibody immobilization as a function of plasma power, monomer pressure and treatment time, and duty cycle. Conditions were optimized by evaluating the surface amine density of plasma polymer coated samples before and after aging in dry ethanol for 3 hrs. In addition, plasma polymer coatings were characterized by contact angle analyzer, α‐step, and FT‐IR/ATR. The continuous wave plasma polymerization provided amine density of 4.8 molecules/nm2 at the optimum condition of 20 W, 1 min, and 60 mTorr, while the pulsed plasma polymerization coating resulted in further increased amine density to 5.2 molecules/nm2 at the duty cycle of 60/100.

Quantitative analysis of surface amine groups on plasma-polymerized ethylenediamine films using UV–visible spectroscopy compared to chemical derivatization with FT-IR spectroscopy, XPS and TOF-SIMS

A quantitative analysis of the surface density of amine groups on a plasma-polymerized ethylenediamine thin film deposited on a platinum surface using inductively coupled plasma chemical vapor deposition method is described. UV–visible spectroscopy together with a chemical derivatization technique using Fourier transform infrared (FT-IR) spectroscopy was used to obtain the quantitative information. Chemical tags of pentafluorobenzaldehyde were hybridized with the surface amine groups and were easily detected due to the characteristic absorption bands of C–F stretching, aromatic ring and C N stretching vibrations in the reflection–absorption FT-IR spectra. The surface amine density was reproducibly controlled as a function of deposition plasma power and quantified using UV–visible spectroscopy. A good linear correlation was observed between the FT-IR intensities of the characteristic absorption bands and the surface amine densities, suggesting the possibility of using this chemical derivatization technique to quantify the surface densities of specific functional groups on an organic surface. Chemical derivatization was also used with X-ray photoelectron spectroscopy on the same samples, and the results were compared with those obtained from FT-IR and time-of-flight secondary ion mass spectrometry. Although each analysis technique has different probing depths from the surface, the three different data sets obtained from the chemical tags correlated well with each other since each analysis technique measured the chemical tags on the sample surface.

Chemical derivatization technique in ToF-SIMS for quantification analysis of surface amine groups

A chemical derivatization technique in ToF-SIMS along with principal component analysis (PCA) were used to perform a quantitative study of the surface amine density of the plasma-polymerized ethylenediamine (PPEDA) thin film. We used the scores on principal component (PC) 1 from a PCA of ToF-SIMS data for the PPEDA films and their chemical-derivatized surfaces for comparison with the surface amine densities. These surface amine densities were independently determined by UV–visible spectroscopy. Our work found a good linear relationship between the surface amine densities and the scores on PC 1 from a PCA of the ToF-SIMS data for the chemical-derivatized PPEDA surfaces, but not for the PPEDA thin films themselves. In addition to quantification, our PCA results provided insights into the surface chemical composition of each surface.

Quantitative Chemical Derivatization Technique in Time-of-Flight Secondary Ion Mass Spectrometry for Surface Amine Groups on Plasma-Polymerized Ethylenediamine Film

A chemical derivatization technique in time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been developed to quantify the surface density of amine groups of plasma-polymerized ethylenediamine thin film deposited on a glass surface by inductively coupled plasma chemical vapor deposition. Chemical tags of 4-nitrobenzaldehyde or pentafluorobenzaldehyde were hybridized with the surface amine groups and were detected in TOF-SIMS spectra as characteristic molecular secondary ions. The surface amine density was controlled in a reproducible manner as a function of deposition plasma power and was also quantified using UV-visible spectroscopy. A good linear correlation was observed between the results of TOF-SIMS and UV-visible measurements as a function of plasma power. This shows that the chemical derivatization technique in TOF-SIMS analysis would be useful in quantifying the surface density of specific functional groups that exist on the organic surface.

Fabrication of amino silane-coated microchip for DNA extraction from whole blood

A simple microchip device for DNA extraction was constructed based on electrostatic interactions between surface amine groups and DNA. Microchannel was fabricated on silicon wafer by photolithography and coated with 3-aminopropyltriethoxysilane (APTES) or 3-[2-(2-aminoethylamino)-ethylamino]-propyltrimethoxysilane (AEEA) to introduce amine groups on the surface. Determination of the number of surface amine groups and optimization of DNA capture condition were demonstrated to characterize the microchip. Capacities of capturing DNA were approximately 97 ng/cm 2 in APTES and 194 ng/cm 2 in AEEA modified microchips, respectively. The amount of DNA captured in the microchip increased depending on surface amine density. Furthermore, DNA extraction using amine-coated microchip from whole blood was examined. Quantification of DNA and proteins in washing or eluting fraction indicates that proteins were removed at washing steps and only DNA was effectively eluted by changing alkalinity of buffer from pH 7.5 to 10.6. The amount of DNA extracted from whole blood was approximately 10 ng and its recovery ratio was 27–40%. Performance of PCR for the eluted fraction indicates that DNA extracted from whole blood was well purified using amine-coated microchip.

Effects of protein-surface interactions on protein ion signals in MALDI mass spectrometry.

The influence of polymer surface-protein binding affinity on protein ion signals in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is examined. The surfaces of poly(vinylidene fluoride) and poly(ethylene terephthalate) polymer substrates are modified by pulsed rf plasma deposition of allylamine. By varying the on/off duty cycle of the pulsed rf plasma, the polymer substrate surfaces are coated with thin films having varying densities of surface amine groups. The varying surface amine density is shown to lead to systematic changes in the surface binding affinity for the 125I-radiolabeled peptides angiotensin I and porcine insulin. Unlabeled angiotensin I and porcine insulin are then deposited on the pulsed rf plasma-modified substrates and analyzed by MALDI mass spectrometry. The experimental approach involves applying the peptide to the modified polymer surface in an aqueous phosphate-buffered saline solution and allowing the peptide solution to dry completely under ambient conditions. Subsequently, the MALDI matrix alpha-cyano-4-hydroxycinnamic acid in methanol and 10% trifluoroacetic acid in water are added to the peptide-coated modified polymer surfaces. The results of these studies demonstrate that, for the sample preparation method employed, increases in the surface peptide binding affinity lead to decreases in the peptide MALDI ion signal.