Dendrimer Monolayer Research Articles

Protein Interaction with Dendrimer Monolayers: Energy and Surface Topology

Protein interaction with polymers layers is a keystone in designing bio-nano devices. Polyamidoamines (PAMAMs) are well-known polymers. Zero aromatic core dendrimers (ZAC) are molecules with no proven toxic effect in cultured cells. When coating nanodevices with enzymatic systems, active sites are disturbed by an interaction with the biosystem surface. Computational methods were used in order to simulate, characterize, and quantify protein–polymer interaction. Protein corona, i.e., surface proteins disposed on a viral membrane or nanodevice outer surface, are crucial in interactions with a potential pharmacological target or receptor. Corona symmetry has been observed in the Middle East respiratory syndrome-related coronavirus (MERS-CoV), severe acute respiratory syndrome coronavirus (SARS-CoV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). As a protein alpha 1 antitrypsin’s a crystallographic structure was chosen. Protein–mono dendrimer layer systems were generated using in silico methods in order to simulate their interaction. Interactions were quantified using topological and quantum mechanical strategies. Results showed that PAMAM and ZAC interact differently with alpha 1 antitrypsin. Energy and topological surfaces of protein vary accordingly with the dendrimer monolayer. Topological surfaces have a higher sensibility in describing the interactions.

Monolayers of poly(amido amine) dendrimers on mica – In situ streaming potential measurements

The deposition of poly(amido amine) dendrimers on mica at various pHs was studied by the atomic force microscopy (AFM) and in situ streaming potential measurements. Bulk characteristics of dendrimers were acquired by using the dynamic light scattering (DLS) and the laser Doppler velocimetry (LDV). The hydrodynamic radius derived from DLS measurements was 5.2nm for the ionic strength of 10−2M and pH range 4–10. The electrophoretic mobility, the zeta potential and the number of electrokinetic charges per molecule were derived as a function of pH from the LDV measurements. It was revealed that the dendrimers are positively charged for pH up to 10. This promoted their deposition on negatively charged mica substrate whose kinetics was quantitatively evaluated by direct AFM imaging and streaming potential measurements interpreted in terms of the electrokinetic model. The desorption kinetics of dendrimers under flowing conditions from monolayers of various coverage was also studied. It was revealed that dendrimer deposition was partially reversible for pH above 5.8. The acid-base properties of the dendrimer monolayers deposited on mica were characterized.

Combining Surface Plasmon Resonance and Quartz Crystal Microbalance To Determine Hydration of Dendrimer Monolayers

Polyelectrolytes are abundant in nature and crucial due to their versatility in biological systems. The controlled assembly of polyelectrolytes has potential applications in the formation of nanostructured and microstructured materials of desired structure and functionality. Dendrimers are a special class of polyelectrolytes, which are characterized by their densely branched and well-defined spherical geometry. Amino-terminal dendrimers resemble spheres, whose uniform surface charge densities can be continuously modulated by pH or ionic strength. The present study focuses on the dendrimer monolayer structure on gold surfaces. We used multiparametric surface plasmon resonance (MP-SPR) and a quartz crystal microbalance with dissipation energy monitoring (QCM-D) to investigate the conformational behavior of the sixth generation of PAMAM molecules. Both the kinetics of dendrimer deposition and the maximum surface concentration were determined. The dependence of the maximum coverage on the pH, ionic strength, ...

PAMAM dendrimers on controlled pore glass: The effect of tethered dendrimer size and tethered affinity groups NTA and terpy on metal ion and indicator dye uptake

PAMAM dendrimer monolayers were covalently immobilized onto controlled pore glass (CPG) particles as platforms to graft the metal ion affinity groups nitrilotriacetic acid (NTA) and terpyridine (terpy). Functional end group analyses, metal ion loading capacities and indicator dye complexation to metal affinity sites were measured as a function of dendrimer size. Metal ions were efficiently extracted from 5ppm solutions flowing through a packed column of modified CPG and loading capacities increased linearly with immobilized dendrimer size at pH 7.2 as determined by atomic absorption spectroscopy. The dendrimer tethered terpy affinity group was surprisingly effective in aqueous solution for extraction of Zn, Cu and Pb ions, but not as effective for Ni ions when compared to tethered NTA. Metal ion indicator dyes bind to the immobilized metal affinity sites showing a generational dependence. Subsequent addition of pyrophosphate releases dye back into solution as a demonstration of an immobilized indicator displacement assay.

Deposition of gallium oxide nanodots prepared from metal-assembling dendrimer molecules isolated by the spacing of the nonmetal-assembling dendrimer molecules in the two-dendrimers mixture monolayer

Phenylazomethine dendrimers (DPA) can precisely incorporate metal chlorides onto the imine sites in a stepwise fashion. Such precise dendrimer–metal complexes allow the preparation of size-controlled subnanometer metal particles. We now propose a novel approach for the fabrication of size-controlled subnanometer metal oxide dots isolated on a substrate using two different-type dendrimers. One is a fourth-generation phenylazomethine dendrimer (DPAG4) and the other is a benzylether dendrimer (BzEG3) with a zinc porphyrin core. Even though the diameter of BzEG3 corresponds to that of DPAG4, BzEG3 has no metal-complexing site. Upon dip coating on a highly oriented pyrolytic graphite substrate by the mixed solution of the metal chloride-assembling DPAG4 molecules and BzEG3 molecules, the dendrimer monolayer was immobilized on the substrate. The concentration of the dendrimer mixture was determined in order to separate each DPAG4–metal chloride complex molecule by BzEG3. Monodispersed metaloxide nanodot arrays could be obtained from the dendrimer monolayer in which DPAG4–metal chloride complex molecule is well isolated by the BzEG3 as a spacer after the hydrolysis of metal chlorides followed by the complete removal of dendrimers. Copyright © 2013 John Wiley & Sons, Ltd.

Novel 3-dimensional dendrimer platform for glycolipid microarray

Glycolipids are important biological molecules that modulate cellular recognitions and pathogen adhesions. In this paper, we report a sensitive glycolipid microarray for non-covalently immobilizing glycolipids on a microarray substrate and we perform a set of immunoassays to explore glycolipid–protein interactions. This substrate utilizes a three-dimensional hydrazide-functionalized dendrimer monolayer attached onto a microscopic glass surface, which possesses the characteristics to adsorb glycoliplids non-covalently and facilitates multivalent attributes on the substrate surface. In the proof-of-concept experiments, gangliosides such as GM1, FucGM1, GM3, GD1b, GT1b, and GQ1b, and a lipoarabinomannan were tested on the substrate and interrogated with toxins and antibodies. The resulting glycolipid microarrays exhibited hypersensitivity and specificity for detection of glycolipid–protein interactions. In particular, a robust and specific binding of a pentameric cholera toxin B subunit to the GM1 glycolipid spotted on the array has demonstrated its superiority in sensitivity and specificity. In addition, this glycolipid microarray substrate was used to detect lipoarabinomannan in buffer within a limit-of-detection of 125ng/mL. Furthermore, Mycobacterium tuberculosis (Mtb) Lipoarabinomannan was tested in human urine specimens on this platform, which can effectively identify urine samples either infected or not infected with Mtb. The results of this work suggest the possibility of using this glycolipid microarray platform to fabricate glycoconjugate microarrays, which includes free glycans and glycolipids and potential application in detection of pathogen and toxin.

Electrochemical Property and Cell Toxicity of Gold Electrode Modified by Monolayer PAMAM Encapsulated Gold Nanorods

Herein we exploit the molecular engineering capability to immobilize monolayer of polyamidoamine dendrimer on gold electrode, which exhibit enhanced charge transfer and biocompatibility. Polyamidoamine (PAMAM generation 5.0) dendrimers were used as template/stabilizers for gold nanoparticle growth, with Au@PAMAMAu @ nanoparticles serving as surface modifier to produce monolayer film. TEM, UV-vis spectroscopy, and AFM were used to characterize the formation of monolayer PAMAM on gold surface. The cyclic voltammetry (CV) and Impedance measurements of Au@PAMAM modified gold electrodes demonstrate electrochemistry properties of modified electrode. Furthermore, Au@PAMAM coating can greatly increased the biocompatibility of gold electrode as determined by cell growth curves.

Interactions between DNA and Poly(amido amine) Dendrimers on Silica Surfaces

This study increases the understanding at a molecular level of the interactions between DNA and poly(amido amine) (PAMAM) dendrimers on solid surfaces, which is a subject of potential interest in applications such as gene therapy. We have used in situ null ellipsometry and neutron reflectometry to study the structure of multilayer arrangements formed by PAMAM dendrimers of generation 2 (G2), 4 (G4), and 6 (G6) and DNA on silica surfaces. Specifically, we adsorbed cationic dendrimer layers, then we condensed DNA to form dendrimer-DNA bilayers, and last we exposed further dendrimer molecules to the interface to encapsulate DNA in dendrimer-DNA-dendrimer trilayers. The dendrimer monolayers formed initially result in the deformation of the cationic adsorbates as a result of their strong electrostatic attraction to the hydrophilic silica surface. The highest surface excess and most pronounced deformation occurs for the G6 molecules due to their relatively large size and high surface charge density. G6-functionalized surfaces give rise to the highest surface excess of DNA during the bilayer formation process. This result is explained in terms of the high number of charged binding sites in the G6 monolayer and the low electrostatic repulsion between DNA and exposed patches of silica surface due to the relatively thick G6 monolayer. The binding strengths of the silica-dendrimer and dendrimer-DNA interactions are demonstrated by the high stability of the interfacial bilayers during rinsing. For the formation of trilayers of dendrimers, DNA, and dendrimers, G2 adsorbs as a smooth layer while G4 and G6 induce the formation of less well-defined structures due to more complex DNA layer morphologies.

Indicator displacement assays for amino acids using Ni–NTA tethered to PAMAM dendrimers on controlled pore glass

PAMAM dendrimer monolayers, immobilized on glass and modified with Ni(II)-NTA moieties at the termini, show generational dependent responses as histidine selective sensors via indicator displacement assays.

Carbohydrate Cluster Microarrays Fabricated on Three-Dimensional Dendrimeric Platforms for Functional Glycomics Exploration

We reported here a novel, ready-to-use bioarray platform and methodology for construction of sensitive carbohydrate cluster microarrays. This technology utilizes a three-dimensional (3-D) poly(amidoamine) starburst dendrimer monolayer assembled on glass surface, which is functionalized with terminal aminooxy and hydrazide groups for site-specific coupling of carbohydrates. A wide range of saccharides, including monosaccharides, oligosaccharides and polysaccharides of diverse structures, are applicable for the 3-D bioarray platform without prior chemical derivatization. The process of carbohydrate coupling is effectively accelerated by microwave radiation energy. The carbohydrate concentration required for microarray fabrication is substantially reduced using this technology. Importantly, this bioarray platform presents sugar chains in defined orientation and cluster configurations. It is, thus, uniquely useful for exploration of the structural and conformational diversities of glyco-epitope and their functional properties.

Novel Carbohydrate Cluster Microarrays Technology for Profiling Glycan Functions

First, we introduce a novel, ready-to-use bioarray platform and methodology for construction of sensitive carbohydrate cluster microarrays. This technology utilizes a 3-dimensional (3-D) poly(amidoamine) starburst dendrimer monolayer assembled on glass surface, which is functionalized with terminal aminooxy and hydrazide groups for site-specific coupling of carbohydrates. A wide range of saccharides, including monosaccharides, oligosaccharides and polysaccharides of diverse structures, are applicable for the 3-D bioarray platform without prior chemical derivatization. The process of carbohydrate coupling is effectively accelerated by microwave radiation energy. The carbohydrate concentration required for microarray fabrication is substantially reduced using this technology. Importantly, this bioarray platform presents sugar chains in defined orientation and cluster configurations. It is, thus, uniquely useful for exploration of the structural and conformational diversities of glyco-epitope and their functional properties. Its potential in glycomics application is demonstrated by chip-display of a panel of glyco-epitopes for highly sensitive detection of carbohydrate-binding proteins and construction of sugar microarrays for differential detection of the Influenza hemagglutinins of H3N1 and H5N1. We will also briefly introduce our recently research on the development of Au glyconanoparticles and fluorescent glycolnanoparticles, as well as the application of the glyconanoparticles for biotoxin detection and bio-imaging.

A sensitive impedimetric thrombin aptasensor based on polyamidoamine dendrimer

A label-free and highly sensitive impedimetric aptasensor based on a polyamidoamine dendrimer modified gold electrode was developed for the determination of thrombin. Amino-terminated polyamidoamine dendrimer was firstly covalently attached to the cysteine functionalized gold electrode through glutaraldehyde coupling. Subsequently, the dendrimer was activated with glutaraldehyde, and amino-modified thrombin aptamer probe was immobilized onto the activated dendrimer monolayer film. The layer-by-layer assembly process was traced by surface plasmon resonance and electrochemical impedance spectroscopy. After electrode preparation, the detection of thrombin was investigated in the presence of the reversible [Fe(CN) 6] 3−/4− redox couple using impedance technique. The results showed that the charge-transfer resistance ( R ct) value had a linear relationship with the concentrations of thrombin in the range of 1–50 nM, and the detection limit (S/N = 3) as low as 0.01 nM was obtained. The covalent immobilization of dendrimer on the electrode surface not only improved the immobilization capacity of probe molecules but also magnified the response signal. The aptasensor exhibited favorable regeneration ability, selectivity and stability. It also showed the detectability in biological fluid.

Preparation of catalytic films of platinum on Au substrates modified by self-assembled PAMAM dendrimer monolayers

In this work we demonstrate the preparation of highly catalytically active Pt formed by the galvanic replacement of the copper adlayer on Au substrates, modified by the self-assembly of fourth generation amine terminated PAMAM dendrimer (G4NH2). The copper adlayer was formed on the dendrimer-modified gold substrate by chemical preconcentration of copper ions followed by electrochemical reduction. The Pt overlayer was characterized by SEM, XPS and by cyclic voltammetry. The catalytic efficiency of the modified film thus prepared through soft route was evaluated by the electro catalytic oxidation of methanol using cyclic voltammetry, chronoamperometry and AC impedance techniques. This work also demonstrates that the copper adlayer formed on the dendrimer-modified electrode can undergo galvanic replacement by nobler metals like Au and Ag, besides Pt. An elegant soft route involving a new three-step protocol to build the concentration of active Pt on the Au surface has been developed. Concentration of the same metal (Pt) or two different metals (Pt–Au) can be built at the interface in a stepwise manner at ambient temperature.

Electrochemical preparation of copper–dendrimer nanocomposites: picomolar detection of Cu2+ ions

The present work describes, for the first time, in situ electrochemical preparation of dendrimer-encapsulated Cu nanoparticles using a self-assembled monolayer of fourth-generation amine-terminated polyamidoamine (PAMAM) dendrimer as the template. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) studies of the modified surface confirmed the presence of Cu nanoparticles entrapped in dendrimer film. Au electrode modified with a monolayer of the dendrimer enables preconcentration and subsequent voltammetric detection of Cu(2+) at picomolar concentrations. Further, Cu nanoparticles in the dendrimer monolayer could be electrochemically derivatised to Cu hexacyanoferrate, which exhibits specific crystal planes, unlike the random distribution of crystal planes in bulk-formed Cu hexacyanoferrate, which is another catalytically active material for sensor applications.

Fabrication of an integrated microfluidic device based on a heat-sensitive poly(N-isopropylacrylamide) polymer and micromachining protocols for programmed bio-molecular patterning

Due to their broad application in biochemical analysis, the miniaturized and integrated microfluidic devices which can give a biochemically active phase for diagnostic capabilities on single chips are very important in contemporary research. Here, we present an integrated microfluidic device applicable to sample preparation, like the controlled patterning of target biomolecules, like proteins or cells, with a smart polymer-modified temperature-addressable microelectrode that is thermally switched between hydrophilic and hydrophobic states. The device is composed of a bulk-micromachined Si device and a hot-cast poly(dimethyl siloxane) (PDMS) device. The microelectrode a array has been integrated into a micro-hot plate having an embedded microheater and temperature sensors on 2-μm thick silicon oxide/silicon nitride/silicon oxide (O/N/O) stacking layer, and is designed to adsorb and release biomolecules with low power consumption and rapidness in a microfluidic chamber. To provide the heat-responsive activity to the microelectrode surface, the electrode surface was modified with poly( N -isopropylacrylamide) (PNIPAAm), which shows a rapidly reversible hydrophilic-to-hydrophobic transition in response to temperature changes. In this study, design, fabrication and its characterization of the microfluidic device with NHS PNIPAAm surface modifications on the dendrimer monolayer conjugated microelectrode were carried out. And then, the synthesis and the confirmation of surface modification with the smart polymer by grazing FT-IR spectroscopy and contact angle analyzer were demonstrated. The microfluidic devices would be directly applicable to a portable battery-powered biochemical system.

PAMAM Dendrimers as Anchors for the Preparation of Electrocatalytically Active Ultrathin Metallic Films

This paper describes the formation of catalytically active thin films of Pt, Pt/Au, and Pt/Ru on gold substrates stabilized by amine-terminated polyamidoamine (PAMAM) dendrimers. A monolayer of dendrimer is initially self-assembled on the gold substrate, which serves as a template for the growth of catalytically active thin films. As dendrimers contain tens to hundreds of functional groups at the periphery, the aggregate strength of the multidentate interactions with the gold substrate leads to the formation of robust films. The films were found to exhibit high catalytic activity for the oxidation of small hydrocarbons such as methanol. Such films offer versatility and scope for the design of effective electrocatalysts, especially in the context of microfuel cells and "dendrichips"; hence, they could find applications in the fields of sensors, fuel cells, and waste-water treatment.

Microcontact printed poly(amidoamine) dendrimer monolayers on silicon oxide surface

Patterning of silicon substrates with poly(amidoamine) generation 5 (PAMAM-G5) dendrimers using soft lithographic microcontact printing (μCP) is presented. μCP is shown to yield monolayers of dendrimers patterned with high level of definition over μm 2 to mm 2 areas. The patterns are stable over a period of weeks, which is attributed to the suppressed diffusion of partially charged G5 PAMAM on oxidized silicon. However, the dendrimers studied were shown to be relatively weakly bound to the substrate when subjected to lateral stresses. In aqueous conditions most of the dendrimers desorbed from the substrate.

Preparation of thin oligopeptide films using self-organized dendrimer monolayer as an anchoring scaffold

Functionalization of a self-organized poly(amidoamine) (PAMAM) dendrimer monolayer with oligopeptides on a silicon/quartz substrate is investigated in this paper. A monolayer of PAMAM dendrimers is formed on a silicon/quartz surface via electrostatic adsorption. The functionalization of the PAMAM monolayer with oligo-tryptophan (Trp) is performed by in situ ring-opening polymerization of Trp– N -carboxyanhydrides (NCAs). The substrates have been examined by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and UV–Vis spectroscopy, which confirm that the self-organized PAMAM dendrimer monolayer can be used as an anchoring scaffold for the construction of thin oligopeptide film.

A tribological study of kinetically influenced ultrathin Au and Cu metal overlayers grown on dendrimer mediated Si

Evidence is presented here for deposition kinetic energy influences on the wear properties of Au and Cu films deposited by evaporation and sputtering on clean and poly(amidoamine) (PAMAM) dendrimer modified SiOx substrates. Ramped load nanoscratch tests show increased resistance to wear in the presence of the dendrimer monolayer. Nanoscratch profiles indicate that the critical load to failure (scratch bearing capacity) is increased in the presence of a dendrimer interlayer. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis of the wear tracks show that following film failure plowing is the predominant mechanism of wear for sputtered or evaporatively deposited Au. No obvious changes in the wear properties (a pure cutting mechanism) of Cu thin films are observed upon changing the kinetic energy of the incoming metal.

Morphological and structural characterizations of dendrimer-mediated metallic Ti and Al thin film nanocomposites

Evidence is presented here for significant influence on the surface topography of Ti and Al films in the presence of poly(amidoamine) dendrimer monolayers [generations G(4–8)] on SiO x . X-ray photoelectron spectroscopy analysis clearly indicates formation of nitrides and carbides for Ti metal grown on dendrimer monolayers. In addition, obvious trends in measured correlation lengths and crystalline growth modes of Ti films indicate grain sizes tracking the intrinsic roughness of dendrimer monolayers. No formation of metal nitride is observed for Al depositions. Atomic force microscopy analyses show significant changes in rms vertical roughness and aggregation of as-deposited Ti or Al in presence of dendrimer monolayers.