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Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

Infrared spectroscopy is used to investigate the transformation of carboxyl-terminated alkyl chains immobilized on a surface into succinimidyl ester-terminated chains by reaction with an aqueous solution of N-ethyl-N'-(3-(dimethylamino)propyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The acid chains are covalently grafted at the surface of hydrogenated porous silicon whose large specific surface area allows for assessing the activation yield in a semiquantitative way by infrared (IR) spectroscopy and detecting trace amounts of surface products and/or reaction products of small IR cross section. In this way, we rationalize the different reaction paths and optimize the reaction conditions to obtain as pure as possible succinimidyl ester-terminated surfaces. A diagram mapping the surface composition after activation was constructed by systematically varying the solution composition. Results are accounted for by NHS surface adsorption and a kinetic competition between the various EDC-induced surface reactions.

Semiquantitative Study of the EDC/NHS Activation of Acid Terminal Groups at Modified Porous Silicon Surfaces

We have developed a facile method for the construction of liquid-phase eutectic gallium–indium (EGaIn) alloy nanoparticles. Particle formation is directed by molecular self-assembly and assisted by sonication. As the bulk liquid alloy is ultrasonically dispersed, fast thiolate self-assembly at the EGaIn interface protects the material against oxidation. The choice of self-assembled monolayer ligand directs the ultimate size reduction in the material; strongly interacting molecules induce surface strain and assist particle cleavage to the nanoscale. Transmission electron microscopy images and diffraction analyses reveal that the nanoscale particles are in an amorphous or liquid phase, with no observed faceting. The particles exhibit strong absorption in the ultraviolet (∼200 nm), consistent with the gallium surface plasmon resonance, but dependent on the nature of the particle ligand shell.

Directing substrate morphology via self-assembly: ligand-mediated scission of gallium-indium microspheres to the nanoscale

Recently, much attention has been given to the development of biofunctionalized nanoparticles with magnetic properties for novel biomedical imaging. Guided, smart, targeting nanoparticulate magneti ...

Synthesis and characterization of PEGylated Gd2O3 nanoparticles for MRI contrast enhancement.

Immobilization of glucose oxidase onto gold nanoparticles with enhanced thermostability

Two N-hydroxysuccinimide (NHS) ester disulfides, 16,16'-dithiobis(N-hydroxysuccinimidylhexadecanoate) (NHS-C15) and 11,11'-dithiobis(N-hydroxysuccinimidylundecanoate) (NHS-C10), were synthesized and adsorbed as self-assembled monolayers (SAMs) on gold surfaces. These SAMs, together with SAMs of 3,3'-dithiobis(N-hydroxysuccinimidylpropionate) (NHS-C2), were used as model systems for an examination of the factors that affect the kinetics of interfacial reactions. The SAMs and the rate of the base-catalyzed hydrolysis of the incorporated NHS ester groups were characterized by grazing incidence reflection Fourier transform infrared (GIR-FTIR) spectroscopy and contact angle measurements. GIR-FTIR spectroscopy shows that SAMs of NHS-C2 and NHS-C10 undergo a pseudo-first-order hydrolysis with second-order rate constants of (61 ± 11) × 10-2 M-1 s-1 and (4.5 ± 0.4) × 10-2 M-1 s-1, respectively. SAMs of NHS-C15 show a sigmoid behavior with a half reaction time of 1700 ± 20 s in 10 mM aqueous NaOH. The rate constants determined based on the contact angle data and application of the Cassie equation are in excellent agreement with the GIR-FTIR spectroscopy results. The increase in conformational order with increasing chain length and the concomitant improvement of packing of the NHS ester end groups, as seen by GIR-FTIR spectroscopy, account for the observed differences in reactivity. Our results imply that surface reactions in SAMs can be controlled via careful design of the adsorbate structure.

Reactivity in the Confinement of Self-Assembled Monolayers: Chain Length Effects on the Hydrolysis of N-Hydroxysuccinimide Ester Disulfides on Gold

A bottom-up fabrication of nanometer-scale dendritic structures via the growth of isolated, nanosized supramolecular structures on gold surfaces is presented. A novel dendritic wedge containing peripheral pyridines and a focal dialkylsulfide chain (9) was synthesized and its coordination chemistry in solution was tested with a second-generation Frechet dendron functionalized with a focal SCS PdII pincer moiety (13). Replacement of the labile acetonitrile in 13 by the pyridine groups of 9 converts dendritic wedge 9 into fourth-generation metallodendron 9 · 134 in one step. Based on these results the spatially confined growth on a gold surface was studied. The dendritic molecules with reactive pyridine groups at the periphery (9) were first spatially isolated by inserting them into decanethiol self-assembled monolayers (SAMs) on a gold surface. Subsequently, the peripheral pyridines were reacted via metal-ligand coordinative interactions by exposing the monolayer to a solution of dendritic wedges containing focal SCS PdII pincer moieties (13). The isolated molecules inserted into the original SAM in the first step were resolved by ex-situ tapping-mode atomic force microscopy (TM-AFM). The subsequent PdII-pyridine coordination resulted in a significant increase in size of the individually resolved molecules. Reference experiments demonstrated that the increased size of the isolated dendrimers on the gold substrate was a result of specific metal-ligand interactions. The methodology presented herein allows the creation of surface-confined architectures and potentially provides a viable complement to currently employed top-down methods in nanofabrication.

Non‐Covalent Chemistry on Surface‐Confined, Isolated Dendrimers

In this contribution we review our recent progress in studies that aim at the understanding of the relationship between structure and surface reactivity of organic thin films on the one hand, and at the micro- and nanofabrication of bioreactive or biocompatible platforms on the other hand. Self-assembled monolayers (SAMs) of n,n′-dithiobis(N-hydroxysuccinimidyl-n-alkanoate) exposing NHS reactive ester groups were studied as model systems for immobilization reactions of DNA, proteins, and receptors. Reaction kinetics and activation energies were determined quantitatively at length scales ranging from millimeters down to nanometers using, for example, surface infrared spectroscopy and in situ inverted chemical force microscopy (iCFM), respectively. The increase in conformational order with increasing alkane segment length was found to result in reduced reactivity due to steric crowding. This drawback of highly organized monolayer architectures and the inherently limited loading can be circumvented by utilizing well-defined macromolecular thin films. Using amine-terminated polyamidoamine (PAMAM) dendrimers immobilized via soft lithography, as well as scanning probe lithography (SPL) approaches (dip-pen nanolithography, DPN) on NHS ester surfaces, robust micrometer and submicrometer patterned (bio)reactive surfaces, which allow one to achieve high molecular loading in coupling reactions for chip-based assays and sensor surfaces, were fabricated. Covalent coupling afforded the required robustness of the patterned assemblies. Finally, we address micro- and nanopatterned bilayer-based systems. SPL was applied in order to fabricate nanoscale biocompatible supramolecular architectures on solid supports. The adsorption of vesicles onto lipid bilayers was spatially controlled and directed in situ with nanometer-scale precision using SPL. This methodology, which provides a platform for research on proteins incorporated in the lipid bilayers comprising the vesicles, does not require that the vesicles are chemically labeled in order to guide their deposition.

Organic and Macromolecular Films and Assemblies as (Bio)reactive Platforms: From Model Studies on Structure-Reactivity Relationships to Submicrometer Patterning

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Papers

Reactivity in the Confinement of Self-Assembled Monolayers: Chain Length Effects on the Hydrolysis of N-Hydroxysuccinimide Ester Disulfides on Gold

Non‐Covalent Chemistry on Surface‐Confined, Isolated Dendrimers

Organic and Macromolecular Films and Assemblies as (Bio)reactive Platforms: From Model Studies on Structure-Reactivity Relationships to Submicrometer Patterning