Dendrimer Monolayer Research Articles

Replication of dendrimer monolayer as nanopores in titania ultrathin film.

An ultrathin titania film with molecular-sized cavities was synthesized by treating a ca. 8 nm thick (TiO2)3(dendrimer)(TiO2)2 sandwich film with activated oxygen gas.

Self-Assembled Multilayer Films Based on Dendrimers with Covalent Interlayer Linkage

Multilayer ultrathin films composed of nitro-containing diazoresin (NDR) as polycation and poly(amidoamine) dendrimers with carboxyl terminal groups (PAMAMC) (G = 1.5, 2.5, 3.5, and 4.5) as polyanion were fabricated on mica by electrostatic layer-by-layer deposition. Subsequent UV irradiation converted the interlayer linkage from ionic to covalent. The films were characterized with UV−vis, FTIR, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and X-ray diffraction (XRD). The results show that the uniform multilayer films were formed. All the films with dendrimers of various generations as building blocks have a very smooth surface with a mean roughness of about 0.8−1.1 nm. The thickness of the PAMAMC−NDR bilayer in the films increases with the generation number of the dendrimer, but the average thickness of the dendrimer monolayer is smaller than the diameter of the ideal spherical model of dendrimers with an extended conformation of all branches. They are significantly compressed i...

Detecting the adsorption of dye molecules in homogeneous poly(propylene imine) dendrimer monolayers by surface plasmon resonance sensor.

In this work, we studied guest-host interactions between various dye molecules and the fifth-generation poly(propylene imine) (PPI-5) dendrimers in aqueous solutions using a surface plasmon resonance (SPR) sensor. The effect of the properties of guest and host molecules (e.g., charge and shape) and media (e.g., pH and ion strength) on affinity between guest and host molecules was investigated. Based on an immobilized homogeneous monolayer of PPI-5 dendrimer tethered to carboxyl-terminal self-assembled monolayers, the adsorption behavior of a group of dye molecules in PPI-5 was obtained. Results show that the strong affinity of PPI-5 to Rose Bengal and erythrosine B is attributed to the good match in charge and shape between the cavities of the dendrimer and the dye molecules. Maximum adsorption around a pH value of 7 was observed. The kinetic behaviors of different dye molecules in dendrimers were also studied. A fundamental understanding of guest-host interactions in dendrimers will guide the design of new-generation sensors and drug delivery carriers.

Reversible affinity interactions of antibody molecules at functionalized dendrimer monolayer: affinity-sensing surface with reusability

We described reversible affinity interactions of antibody molecules at a chemically functionalized electrode surface for a repeatedly renewable affinity–biosensing interface. Underlying biofunctionalizable monolayers were constructed with poly(amidoamine) dendrimers, whose surface chain-end groups were double-functionalized with biotinyl ligand and ferrocenyl groups for biospecific recognition and electron transfer reactions, respectively. Functionalized monolayers on gold electrodes provide platform surfaces for biospecific recognition reaction with monoclonal anti-biotin antibody molecules. Bound antibody molecules were dissociated from the surface via displacement reaction by the addition of free biotin in solution, enabling the affinity surface to be renewed and repeatedly utilized. Tracking of the association/dissociation reaction cycles were performed by registering the bioelectrocatalytic currents at the electrode using glucose oxidase (GO x) as a signal generator and ferrocenyl-tethered dendrimer (Fc-D) as an electron transferring mediator in electrolyte. Shielding of the affinity surface by biospecifically bound antibody molecules caused hindrance in electron transfer, resulting in reduced signal from cyclic voltammetry. By the displacement reaction using free biotin, bound antibody molecules were dissociated from the surface and the bioelectrocatalytic signal was restored. With the affinity surfaces constructed in this work, continuous association/dissociation reactions have been successfully accomplished, providing a possibility of reusable affinity biosensing interface.

The Nanomechanical Effect of Dendrimer Interlayers Underneath Cu Ultrathin Films

ABSTRACTTwo kinds of dendrimers, DAB and PAMAM (with the same terminal groups but different branched repeat units), were chosen as interlayers for Cu ultrathin films deposited on native oxide Si(100) wafers. 10 nm Cu thin films were deposited directly on the dendrimer monolayers by DC sputtering at room temperature. The nanomechanical results show that PAMAM and DAB have significant effects on the properties of the resulting films, with the DAB layer acting as a stiffer ‘spring’, compared to PAMAM, underneath the Cu films. Both dendrimer interlayers lower the hardness of the film, compared to Cu alone; the effect is greater for PAMAM than DAB interlayers. However, the introduction of either dendrimer monolayer significantly increased the elasticity of the Cu film.

Thin Metal Films Deposited on Dendrimer Monolayers

Chemical interactions and the evolution of surface morphology resulting from deposition of Cr and Co onto dendrimer monolayers have been investigated by XPS, RAIRS, and AFM. Evidence is presented for formation of metal nitrides and mediation of film morphology as a function of the metal and generation number of the dendrimer comprising the monolayer.

Molecular Interlayers and the Mechanism of Abrasive Wear of Ultrathin Metal Films

Striking differences have been observed in the deformation modes associated with nanoscratch events on ultrathin Cu layers deposited on SiOx with and without a dendrimer interlayer. In the absence of the dendrimer monolayer significant lateral deformation and distinct ridge formation along the wear track indicative of plowing and wedge formation are observed. By contrast, dendrimer monolayer-mediated films exhibit restricted lateral deformation yielding ridgeless scratches apparently formed in a nearly pure cutting mode.

The Study on the Optical Characteristics of G4-48 Azo Dendrimer by Langmuir-Blodgett Method

In this study, we synthesized dendrimers containing light switchable units, azobenzene group(G4 48-Azo dendrimer). Their chemical structure was verified by using NMR study and UV spectroscopy. To apply to the molecular level switching device or data storage system using Langmuir-Blodgett(LB) film, we investigated the monolayer behavior using π-A isotherm at air/water interface. The surface pressure was also measured during light irradiation. As a result, the G4 48-Azo dendrimer monolayer showed the reversible photo-switching behavior by the isomerization of azobenzene group in their periphery.

Electro-Chemical Properties of Metal Complex Effect in G4-48 Crown-4 Dendrimer Monolayers

In the electro-chemical properties, this increase indicates an increase in the capacity for dendrimer monolayer, confirming the complex of metal ion. The AFM images show the differences in the surface morphology between dendrimer and included Li + monolayers. Importantly, these results conclusively demonstrate that the surface of the dendrimer-encapsulated Li + and Cs + . The current increased with the applied voltage and with metal ion complex.

The Study on the Optical Characteristics of G4-48 Azo Dendrimer by Langmuir-Blodgett Method

In this study, we synthesized dendrimers containing light switchable units, azobenzene group(G4 48-Azo dendrimer). Their chemical structure was verified by using NMR study and UV spectroscopy. To apply to the molecular level switching device or data storage system using Langmuir-Blodgett(LB) film, we investigated the monolayer behavior using π-A isotherm at air/water interface. The surface pressure was also measured during light irradiation. As a result, the G4 48-Azo dendrimer monolayer showed the reversible photo-switching behavior by the isomerization of azobenzene group in their periphery.

Electro-Chemical Properties of Metal Complex Effect in G4-48 Crown-4 Dendrimer Monolayers

In the electro-chemical properties, this increase indicates an increase in the capacity for dendrimer monolayer, confirming the complex of metal ion. The AFM images show the differences in the surface morphology between dendrimer and included Li + monolayers. Importantly, these results conclusively demonstrate that the surface of the dendrimer-encapsulated Li + and Cs + . The current increased with the applied voltage and with metal ion complex.

Photoisomerization of Azobenzene Dendrimer Monolayer Investigated by Maxwell Displacement Current Technique

Photoisomerization in monolayers of a novel azobenzene compound, azobenzene dendrimer, was investigated for the first time by means of the absorption spectrum and Maxwell displacement current (MDC) technique. According to the absorption spectrum, trans-to-cis conversion ratio was estimated to be approximately 10% for the third generation of azobenzene dendrimer deposited onto a glass substrate. Temperature-dependent induced charge with trans-cis isomerization was also measured by means of MDC technique, and we found that the thermal isomerization process must be taken into account for theoretical analysis of trans-to-cis photoisomerization. The temperature dependence was theoretically treated in terms of the three-state model that takes into account the stimulated thermal isomerization. As a result, we could obtain a ground state energy barrier of 0.93 eV in cis-to-trans isomerization for the first-generation of the azobenzene dendrimer (AZ-G1), and the value is in good agreement with the previous results obtained from the molecular orbital (MO) calculation which suggests that thermal cis-to-trans isomerization in AZ-G1 passes through the inversion process.

Dendrimer-mediated growth of very flat ultrathin Au films

Si wafers covered with a native oxide were used as substrates for growth of 12.5nm of evaporated Au (Au/SiOx), and self-assembly of a dendrimer monolayer followed by the same thickness of Au (Au/dendrimer/SiOx). This paper presents evidence for very significant improvements in Au film quality when grown on a self-assembled monolayer of amine-terminated poly(amidoamine) (PAMAM) dendrimers (generation G8) on SiOx. An increase in surface hardness from 1.7 to 3GPa, a decrease in surface roughness from about 1.2 to 0.4nm and better adhesion are shown with a combination of XPS, X-ray reflectivity (XRR), AFM, and nanoindentation. The improvement in film quality may be explained by penetration of the deposited Au into the dendrimer adlayer. This interpenetration is confirmed by AFM profilometry and XPS analysis.

Reversible Association/Dissociation Reaction of Avidin on the Dendrimer Monolayer Functionalized with a Biotin Analogue for a Regenerable Affinity-Sensing Surface

A new approach to a repeatedly regenerable affinity-sensing surface was developed based on the reversible association/dissociation reactions between avidin and biotin analogues. For the affinity surface, a fourth generation poly(amidoamine) dendrimer monolayer was first constructed on the 11-mercaptoundecanoic acid self-assembled monolayer on gold. The dendritic surface amine groups then were functionalized with biotin analogues, desthiobiotin (1), or newly synthesized desthiobiotin amidocaproate (2), an extended form of 1, which shows lower affinity toward avidin. To test the association/dissociation reaction cycles at the affinity surface, avidin adlayer was formed onto the biotin analogue functionalized surface and displaced with free biotin. To trace the stepwise reactions, biotinylated glucose oxidase (b-GOx) as a model enzyme was loaded onto the affinity surface, and cyclic voltammetric measurements were performed by registering the activity of the associated b-GOx. The efficient association/dissociation reaction cycles were registered, especially for the 2-modified electrodes, implying steric hindrance from the ligand length for biospecific interaction. With the optimized affinity-surface construction steps and reaction conditions, continuous association/dissociation reaction cycles were achieved, resulting in a regenerable affinity surface.

Glucose biosensors based on dendrimer monolayers.

The peculiarities of glucose biosensors based on different generation of dendrimers (G0, G1 and G4) have been studied by amperometry and QCM techniques. It is shown that stable glucose biosensor can be obtained with low generation of dendrimers. The sensor sensitivity, however considerable, increased with increasing number of generation of dendrimers. This can be due to the increased volume of the dendrimer interior as well as with increased number of binding sites for glucose oxidase (GOX). QCM experiments showed that immobilization of GOX resulted in formation of enzyme multilayers on a dendrimer surface. The enzyme turnover for this system (0.1-0.01 s(-1)) was lower then that for immobilization of GOX onto a supported lipid films by means of avidin-biotin technology (1.1 s(-1)). However, dendrimer based biosensors are more stable in comparison with sBLM based sensors and could be stored in a refrigerator in dry conditions over 15 days without substantial loss of sensitivity.

Nanoscratch Behavior of Sputtered Metal Films on PAMAM Dendrimer Monolayers

ABSTRACTStriking differences have been observed in the deformation modes associated with 2mN constant load nanoscratch events on ultrathin Cr layers deposited on SiOx with and without a dendrimer interlayer. In the absence of the dendrimer distinct ridge formation along the wear track indicative of plowing and wedge formation are observed. By contrast, dendrimer monolayer-mediated films exhibit ridgeless scratches apparently formed in a nearly pure cutting mode. In addition, the width of the scratch trench in the sample without dendrimer is larger than the one with dendrimer.

Dendritic Amphiphiles: Dendrimers Having an Amphiphile Structure in Each Unit

We have developed a novel approach for forming dendrimer monolayers. A Lys-Lys-Glu tripeptide with a dioctadecylamino tail at the C-terminal and an acetyl head at the N-terminal was newly synthesiz...

Synthesis and Surface Chemistry Study of a New Amphiphilic PAMAM Dendrimer

A new disk-shaped amphiphilic dendrimer has been synthesized by attaching sixty-four 12-hydroxydodecanoic acid chains to a fourth generation poly(amido amine) (PAMAM) dendrimer core. Surface pressure and surface potential−area isotherm measurements have shown that the dendrimer forms a stable monolayer at the air/water interface with limiting molecular area of 160 Å2/molecule. This small area relative to the huge size of the dendrimer suggests that the dendrimer molecules form an edge-on disk-shaped structure at the air/water interface. The topography of the dendrimer monolayer was observed by Brewster angle microscopy (BAM) at air/water interface as well as by environmental scanning electron microscopy (ESEM) as a Langmuir−Blodgett film. The striplike monolayer domains observed from BAM images correspond to the monolayer topography as observed from ESEM images.

Synthesis and Preparation of Ionically Bound Dendrimer Monolayers and Application toward Scanning Probe Lithography

Dendrimer monolayers have been designed for use as positive resists for scanning probe lithography (SPL). Several new amphiphilic poly(benzyl ether) dendrimers with carboxylic acids at either the focal point or the “periphery” have been prepared. These can form ionically bound dendrimer monolayers that may serve as either positive or negative tone resists for SPL. The amphiphilic dendrimers self-assemble onto (3-aminopropyl)silanized Si(100) wafer surfaces to afford ultrathin films. The dendrimer monolayers were characterized by AFM, ellipsometry, and contact angle goniometry. Patterning a singly charged dendrimer monolayer results in the formation of positive tone holes ∼35 nm in width. Similarly, patterning a multiply charged dendrimer monolayer in a direct-write manner with the scanning probe microscope results in the formation of negative tone oxide features ∼80 nm in width.

Time-Dependent Phase Segregation of Dendrimer/n-Alkylthiol Mixed-Monolayers on Au(111): An Atomic Force Microscopy Study

The two-dimensional phase behavior of mixed-monolayers composed of poly(amidoamine) (PAMAM) dendrimers and n-alkylthiols adsorbed to Au(111) surfaces was studied using tapping mode atomic force microscopy (TM-AFM). Mixed-monolayers were prepared by sequential immersion of Au(111) substrates into ethanolic solutions of, first, dendrimers and then n-alkylthiols. Films were prepared by systematically varying the dendrimer generation (G4, G6, and G8) and the n-alkylthiol chain length (CH3(CH2)xSH; x = 4, 11, 15). TM-AFM was used to monitor time-dependent morphological changes in the mixed-monolayers. Dendrimer monolayers immersed in hexane solutions of n-alkylthiols do not phase separate to an appreciable extent, which demonstrates the important role of dendrimer solvation in these processes. In contrast to the amine-terminated dendrimer monolayers, thiol-terminated dendrimers do not phase separate when exposed to ethanolic n-alkylthiol solutions, suggesting that one of the driving forces for this process is ...