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This study describes that the current rectification ratio, R ≡ |J|(-2.0 V)/|J|(+2.0 V) for supramolecular tunneling junctions with a top-electrode of eutectic gallium indium (EGaIn) that contains a conductive thin (0.7 nm) supporting outer oxide layer (Ga2O3), increases by up to four orders of magnitude under an applied bias of >+1.0 V up to +2.5 V; these junctions did not change their electrical characteristics when biased in the voltage range of ±1.0 V. The increase in R is caused by the presence of water and ions in the supramolecular assemblies which react with the Ga2O3/EGaIn layer and increase the thickness of the Ga2O3 layer. This increase in the oxide thickness from 0.7 nm to ∼2.0 nm changed the nature of the monolayer-top-electrode contact from an ohmic to a non-ohmic contact. These results unambiguously expose the experimental conditions that allow for a safe bias window of ±1.0 V (the range of biases studies of charge transport using this technique are normally conducted) to investigate molecular effects in molecular electronic junctions with Ga2O3/EGaIn top-electrodes where electrochemical reactions are not significant. Our findings also show that the interpretation of data in studies involving applied biases of >1.0 V may be complicated by electrochemical side reactions which can be recognized by changes of the electrical characteristics as a function voltage cycling or in current retention experiments.

In this contribution, optically active and paramagnetic micelles of the ligand 1,4,7,10-tetraaza-1-(1-carboxymethylundecane)-4,7,10-triacetic acid cyclododecane (DOTAC10) have been incorporated inside capsids of the cowpea chlorotic mottle virus (CCMV) protein through a hierarchical process of self-assembly triggered by self-assembly. The DOTAC10 ligand was used to complex Gd(III), in order to form paramagnetic micelles, as well as to encapsulate an amphiphilic Zn(II) phthalocyanine (ZnPc) dye that optically confirmed the encapsulation of the micelles. The incorporation of ZnPc molecules in the paramagnetic micelles led to high capsid loading of both Gd(III) and ZnPc, as the micelles were stabilized by the amphiphilic dye encapsulation. The resulting protein cage nanoparticles (PCNs) show an improved r1 relaxivity, suggesting the possible use of these nanostructures as contrast agents (CAs) for magnetic resonance imaging (MRI). Since the encapsulated ZnPc dye also has a potential therapeutic value, the present results represent a first step towards the consecution of fully self-assembled PCNs for multimodal imaging and therapy., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Competition with a monovalent cyclodextrin host (blue cones) in solution drives the multivalent binding of a Eu(3+) complex and a sensitizer molecule to cyclodextrin monolayers through a nonlinear self-assembly process. Adamantyl groups (light-blue spheres) are attached to the EDTA ligand (black) and the antenna molecule (orange), which has a carboxylate group for coordination to the Eu(3+) ion (yellow or red in free or complexed form, respectively)., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Variable-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) measurements are performed on heptathioether β-cyclodextrin (β-CD) self-assembled monolayers (SAMs) on Au. The β-CD molecules exhibit very rich dynamical behavior, which is not apparent in ensemble-averaged studies. The dynamics are reflected in the tunneling current-time traces, which are recorded with the STM feedback loop disabled. The dynamics are temperature independent, but increase with increasing tunneling current and sample bias, thus indicating that the conformational changes of the β-CD molecules are induced by electrons that tunnel inelastically. Even for sample biases as low as 10 mV, well-defined levels are observed in the tunneling current-time traces. These jumps are attributed to the excitations of the molecular vibration of the macrocyclic β-CD molecule. The results are of great importance for a proper understanding of transport measurements in SAMs., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Alkylphosphate self-assembled monolayers (SAMs) were prepared on Nb-doped SrTiO(3) (Nb-STO) conducting metal oxide substrates. Unlike thiols on gold, the alkylphosphate SAMs on Nb-STO exhibited an electrochemical stability over a wide voltage range from -2 to 2 V. Cyclic voltammetry showed that the SAM modification inhibited the electrochemical activity of the underlying conducting substrate with an efficiency dependent on the chain length. Impedance spectroscopy showed that SAM-modified Nb-STO substrates have a significantly higher resistance than bare substrates.

Dip-pen nanolithography (DPN) is an atomic force microscopy (AFM)-based lithography technique, which has the ability to fabricate patterns with a feature size down to approximately 15 nm using both top-down and bottom-up approaches. DPN utilizes the water meniscus formed between an AFM tip and a substrate to transfer ink molecules onto surfaces. A major application of this technique is the fabrication of micro- and nano-arrays of patterned biomolecules. To achieve this goal, a variety of chemical approaches has been used. This review concisely describes the development of DPN in the past decade and presents the related chemical strategies that have been reported to fabricate biomolecular patterns with DPN at micrometer and nanometer scale, classified into direct- and indirect DPN methodologies, discussing tip-functionalization strategies as well., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The kinetics of multivalent (multisite) interactions at interfaces is poorly understood, despite its fundamental importance for molecular or biomolecular motion and molecular recognition events at biological interfaces. Here, we use fluorescence microscopy to monitor the spreading of mono-, di- and trivalent ligand molecules on a receptor-functionalized surface, and perform multiscale computer simulations to understand the surface diffusion mechanisms. Analogous to chemotaxis, we found that the spreading is directional (along a developing gradient of vacant receptor sites) and is strongly dependent on ligand valency and concentration of a competing monovalent receptor in solution. We identify multiple surface diffusion mechanisms, which we call walking, hopping and flying. The study shows that the interfacial behaviour of multivalent systems is much more complex than that of monovalent ones.

PNAs (peptide nucleic acids) have been immobilized onto surfaces in a fast, accurate way by employing reactive microcontact printing. Surfaces have been first modified with aldehyde groups to react with the amino end of the synthesized PNAs. When patterning fluorescein-labeled PNAs by reactive microcontact printing using oxygen-oxidized polydimethylsiloxane stamps, homogeneous arrays were fabricated and characterized using optical methods. PNA-patterned surfaces were hybridized with complementary and mismatched dye-labeled oligonucleotides to test their ability to recognize DNA sequences. The stability and selectivity of the PNA-DNA duplexes on surfaces have been verified by fluorescence microscopy, and the melting curves have been recorded. Finally, the technique has been applied to the fabrication of chips by spotting a PNA microarray onto a flat PDMS stamp and reproducing the same features onto many slides. The chips were finally applied to single nucleotide polymorphism detection on oligonucleotides.

Controlled assembly of ferromagnetic nanoparticles on surfaces is of crucial importance for a range of spintronic and data storage applications. Here, we present a novel method for assembling monolayers of ferromagnetic FePt nanoparticles on silicon oxide substrates using "click chemistry". Reaction of alkyne-functionalized FePt nanoparticles with azide-terminated self-assembled monolayers (SAMs), on silicon oxide, leads to the irreversible attachment of magnetic nanoparticles to the surface via triazole linkers. Based on this covalent interaction, well-packed monolayers of FePt nanoparticles were prepared and nanoparticle patterns are generated on surfaces via microcontact printing (μCP).

We report here the use of nanomolding in capillaries (NAMIC) coupled with dithiocarbamate (DTC) chemistry to fabricate sub-50 nm quasi-1D arrays of 3.5 nm core gold nanoparticles (Au NPs) over large areas. Owing to chemical immobilization via the DTC bond, the patterned NP systems are stable in water and organic solvents, thus allowing the surface modification of the patterned Au NP arrays through thiol chemistry and further orthogonal binding of proteins. The electrical properties of these patterned Au NP wires have also been studied. Our results show that NAMIC combined with surface chemistry is a simple but powerful tool to create metal NP arrays that can potentially be applied to fabricate nanoelectronic or biosensing devices.

The lipase from Candida Rugosa was immobilized to a poly(methacrylic acid) polymer brush layer, grown on the inner wall of silicon-glass microreactors. The hydrolysis of 4-nitrophenyl acetate was used as a model reaction to study the activity of this biocatalytic system. The amount of bound lipase could be tuned by changing the polymerization time of the brush formation. The Michaelis-Menten constants and V(max) values, determined for immobilized and free lipase, are similar, demonstrating that the lipase's substrate affinity and its activity remain unchanged upon immobilization to the microchannel wall.

Detection of an analyte via supramolecular host-guest binding and quantum dot (QD)-based fluorescence resonance energy transfer (FRET) signal transduction mechanism is demonstrated. Surface patterns consisting of CdSe/ZnS QDs functionalized at their periphery with β-cyclodextrin (β-CD) were obtained by immobilization of the QDs from solution onto glass substrates patterned with adamantyl-terminated poly(propylene imine) dendrimeric "glue." Subsequent formation of host-guest complexes between vacant β-CD on the QD surface and an adamantyl-functionalized lissamine rhodamine resulting in FRET was confirmed by fluorescence microscopy, spectroscopy, and fluorescence lifetime imaging microscopy (FLIM).

A polymer-brush-based material was applied for the formation and in situ immobilization of silver and palladium nanoparticles, as a catalytic coating on the inner wall of glass microreactors. The brush film was grown directly on the microchannel interior by means of atom-transfer radical polymerization (ATRP), which allows control over the polymer film thickness and therefore permits the tuning of the number of nanoparticles formed on the channel walls. The wide applicability of the catalytic devices is demonstrated for the reduction of 4-nitrophenol and for the Heck reaction.

We here report the synthesis and structural characterization of the first iridium(III) complex with a caged ligand structure, which shows a 80% decrease of oxygen quenching compared to the archetypical Ir(ppy)(3).

The creation of cyclodextrin patterns on a fluorescent reporter surface by microcontact printing provides a versatile orthogonal surface modification method. The alkyne-beta-cyclodextrin surface is prepared through a "click" reaction on alkyne-terminated coumarin monolayers. The resulting alkyne-beta-cyclodextrin surface can be functionalized through supramolecular microcontact printing on cyclodextrin host patterns and by reactive microcontact printing-induced click chemistry on the alkyne-terminated patterns. The orthogonal covalent and supramolecular "host-guest" functionalization of the surface, and its specificity as well as selectivity, is demonstrated by sequential and one-step printing procedures.

A new approach for fabricating porous structures on silicon substrates and on polymer surfaces, using colloidal particle arrays with a polymer mask of a highly etch-resistant organometallic polymer, is demonstrated. Monolayers of silica particles, with diameters of 60 nm, 150 nm, 300 nm, or 500 nm, were deposited either on a silicon substrate or on a surface coated with polyethersulfone (PES), and the voids of the arrays were filled with poly(ferrocenylmethylphenylsilane) (PFMPS). Argon ion sputtering removed the excess PFMPS on the particles which enabled removal of the particles with HF. Further pattern transfer steps with reactive ion etching for different time intervals provided structures in silicon or in a PES layer. Free-standing PES membranes exhibiting regular arrays of circular holes with high porosity were fabricated by using cellulose acetate as a sacrificial layer. The pores obtained on silicon substrates after etching were used as molds for nanoimprint lithography (NIL). A combination of the techniques of nanosphere lithography (NSL) and NIL has resulted in 3D nanostructures with a hemispherical shape (inherited from the nanoparticles) which was obtained both in silicon and in PMMA.

Electrochemical properties of core-shell CdSe/ZnS quantum dots (QDs) in a non-aqueous solution are presented. Cathodic reduction and anodic oxidation processes involving the QD HOMO and LUMO levels as well as defect states were identified by cyclic voltammetry. The electrochemical bandgap was estimated from the anodic and cathodic redox peaks and found to match well with the optical bandgap estimated from the absorption spectrum. The trioctylphosphine oxide ligands on the surface of the QDs were exchanged to electroactive ferrocenyl thiols and the resulting material was characterized by NMR and optical spectroscopy. Cyclic voltammetry showed that the redox potentials of the QDs are modified due to the presence of ferrocene on the surface of the QD. The QD oxidation peak decreased and the reduction peak shifted to more negative potentials. The concurrent shift of the ferrocene redox peaks indicates that the system displays features of a 'molecular hybrid', where both the QD and the ligand influence each other.

FePt nanoparticles (NPs) were assembled on aluminum oxide substrates, and their ferromagnetic properties were studied before and after thermal annealing. For the first time, phosph(on)ates were used as an adsorbate to form self-assembled monolayers (SAMs) on alumina to direct the assembly of NPs onto the surface. The Al(2)O(3) substrates were functionalized with aminobutylphosphonic acid (ABP) or phosphonoundecanoic acid (PNDA) SAMs or with poly(ethyleneimine) (PEI) as a reference. FePt NPs assembled on all of these monolayers, but much less on unmodified Al(2)O(3), which shows that ligand exchange at the NPs is the most likely mechanism of attachment. Proper modification of the Al(2)O(3) surface and controlling the immersion time of the modified Al(2)O(3) substrates into the FePt NP solution resulted in FePt NPs assembly with controlled NP density. Alumina substrates were patterned by microcontact printing using aminobutylphosphonic acid as the ink, allowing local NP assembly. Thermal annealing under reducing conditions (96%N(2)/4%H(2)) led to a phase change of the FePt NPs from the disordered FCC phase to the ordered FCT phase. This resulted in ferromagnetic behavior at room temperature. Such a process can potentially be applied in the fabrication of spintronic devices.

An indirect method of protein patterning by using Ni(II) ion templates for immobilization via a specific metal-protein interaction is described. A nitrilotriacetic acid (NTA)-terminated self-assembled monolayer (SAM) allows oriented binding of histidine-tagged proteins via complexation with late first-row transition metal ions, such as Ni(II). Patterns of nickel(II) ions were prepared on NTA SAM-functionalized glass slides by microcontact printing (microCP) and dip-pen nanolithography (DPN) to obtain micrometer and submicrometer scale patterns. Consecutive dipping of the slides in 6His-protein solutions resulted in the formation of protein patterns, as was subsequently proven by AFM and confocal fluorescence microscopy. This indirect method prevents denaturation of fragile biomolecules caused by direct printing or writing of proteins. Moreover, it yields well-defined patterned monolayers of proteins and, in principle, is indifferent for biomolecules with a high molecular weight. This approach also enabled us to characterize the transfer of Ni(II) ions on fundamental parameters of DPN, such as writing speeds and tip-surface contact times, while writing with the smallest possible ink "molecules" (i.e., metal ions).

Supramolecular microcontact printing was used to obtain controlled patterns consisting of quantum dots (QDs) functionalized at their periphery with beta-cyclodextrin (beta-CD) in combination with adamantyl terminated dendrimeric "glues". Functionalization of core--shell CdSe/ZnS QDs was achieved by surface ligation. Immobilization of the QDs from solution onto glass substrates printed with (a) adamantyl-terminated poly(propylene imine) dendrimers and (b) via direct microcontact printing of QDs onto the dendrimer layer both yielded stable and robust multilayer structures. The stability of the patterns was primarily due to multivalent supramolecular host--guest interactions between beta-CD located at the QD surface and adamantyl groups at the dendrimer periphery as the dendrimers acted as a "supramolecular glue". The surface-immobilized QDs were capable of forming host--guest complexes with other molecules of interest at binding cavities not occupied by adamantyl groups. Complex formation with ferrocene-functionalized molecules at these sites led to partial quenching of the luminescence emission of QDs demonstrating the principle for sensing using the QD multilayer structures.

A polyelectrolyte multilayer was assembled on top of a patterned PDMS stamp employing the layer-by-layer (LbL) assembly technique. By post-treatment with a base and further cross-linking, a porous multilayer-coated PDMS composite stamp was obtained. With the pore structures acting as an ink reservoir, the multiple printing of proteins was successfully achieved without the need to re-ink the stamp.

Assembly of a mixture of guest-functionalized antenna and Eu(3+)-complexed ligand molecules in a patterned fashion onto a receptor surface provides efficient localized sensitized emission. Coordination of a carboxylate group of the antenna to the Eu(3+) center and noncovalent anchoring of both components to the receptor surface appeared to be prerequisites for efficient energy transfer. A Job plot at the surface confirmed that coordination of the antenna to the Eu(3+) center occurs in a 1:1 fashion. The efficiency of this intramolecular binding process is promoted by the high effective concentration of both complementary moieties at the surface. The system constitutes therefore an example of supramolecular expression of a complex consisting of several different building blocks which signals its own correct formation.

Magnetic nanoparticles are of great scientific and technological interest. The application of ferromagnetic nanoparticles for high-density data storage has great potential, but energy efficient synthesis of uniform, isolated, and patternable nanoparticles that remain ferromagnetic at room temperature is not trivial. Here, we present a low-temperature solution synthesis method for FePtAu nanoparticles that addresses all those issues and therefore can be regarded as an important step toward applications. We show that the onset of the chemically ordered face-centered tetragonal (L1(0)) phase is obtained for thermal annealing temperatures as low as 150 degrees C. Large uniaxial magnetic anisotropy (10(7) erg/cm(3)) and a high long-range order parameter have been obtained. Our low-temperature solution annealing leaves the organic ligands intact, so that the possibility for postanneal monolayer formation and chemically assisted patterning on a surface is maintained.

This paper describes a method for the direct transfer of biomolecules encapsulated within a viscous fluid matrix by dip-pen nanolithography (DPN). The method relies on the use of agarose as a "universal" carrier that is compatible with many types of biomolecules including proteins and oligonucleotides. Agarose-assisted DPN allows one to generate nanoarrays of such materials on activated glass substrates with the same deposition rates for different biomolecules, which will greatly expand future capabilities for parallel, multiplexed biomolecule deposition. The fluidity of the matrix may be systematically varied to control the deposition process, resulting in an additional parameter affecting deposition rates besides tip-substrate contact-time and humidity. Agarose-assisted DPN results in extremely fast biomolecule patterning with typical contact times less than 1 s. Feature sizes as small as 50 nm are demonstrated. The biorecognition properties of both protein and oligonucleotide structures are characterized by studying their reactivity with fluorophore-labeled antibody and complementary oligonucleotide sequences, respectively.

The treatment of a suspension of graphite oxide (GO) with sodium azide leads to a material that, after reduction, features amino groups at the top and bottom of the sheets. These groups react through microcontact printing with an isothiocyanate monolayer on a silicon oxide substrate to form covalent bonds that strongly attach to the particles on the surface. With ultrasonication it is possible to obtain exfoliation of the sheets that are not covalently bound to the surface leaving single-layer platelets attached to the substrate. The azido derivative can be also used to functionalize the graphene oxide with long alkylic chains through a click chemistry approach. This functionalization results in the exfoliation of this material in dimethylformamide. The novel materials were fully characterized by different techniques including IR spectroscopy, thermogravimetric analysis (TGA), scanning and transmission electron microscopy (SEM and TEM), X-Ray photoelectron spectroscopy (XPS), and solid state NMR spectroscopy. The material with amino groups, after the reduction step, is conductive with a resistivity only approximately seven times larger than that of unprocessed graphite. This implies that after reduction of the GO, the conjugated sp2 network is largely restored. We consider this to be an important step towards a chemical approach for forming conducting large-area platelet films of single-layer graphene.

A simple and novel method for fabricating nanoporous-structure-coated silicon nitride tips for dip-pen nanolithography (DPN) by using the layer-by-layer (LbL) technique has been developed. The pore sizes can be adjusted by treating the LbL films coated onto the amino-terminated self-assembled monolayer (NH(2)-SAM)-functionalized AFM tip surface with a base solution for different periods of time. This hydrophilic porous material can absorb biomolecules easily and also provides a larger-volume ink reservoir compared with a bare silicon nitride tip. Proof-of-concept of the porous AFM tip is demonstrated by using fluorescent proteins as ink molecules to fabricate protein patterns at the micrometer and submicrometer length scales.

Freestanding particle bridges with controlled composition and macroscopic robustness are demonstrated by the use of supramolecular nanoparticle assembly. Self-assembly of nanoparticles, templating, and supramolecular glue infiltration are combined to form stable and ordered three-dimensional polystyrene particle composites on a polydimethylsiloxane stamp. Freestanding hybrid polystyrene nanoparticle bridges are obtained by transfer printing of the hybrid structures onto topographically patterned substrates via host-guest interactions. The mechanical robustness and rigidity of the particle bridges can be controlled by manipulating the layer-by-layer cycles of supramolecular glues of gold nanoparticles and dendrimers. Atomic force microscopy-based microbending results, in particular the location and force-dependent deflection behavior, confirm that the particle bridge fulfills the classical supported-beam characteristics. As estimated from classical beam theory, the bending moduli of the particle bridges vary between 0.8 and 1.1 GPa, depending on the degree of filling by the supramolecular glues. Failure analysis on the particle structure indicates linear elastic behavior and a plastic deformation upon failure.

Mechanically robust and crystalline supramolecular particle structures have been constructed by decoupling nanoparticle assembly and supramolecular glue infiltration into a sequential process. First, beta-cyclodextrin (CD)-functionalized polystyrene particles (d approximately 500 nm) were assembled on a CD-functionalized surface via convective assembly to form highly ordered, but mechanically unstable, particle crystals. Subsequently, the crystals were infiltrated by a solution of adamantyl-functionalized dendrimers, functioning as a supramolecular glue to bind neighboring particles together and to couple the entire particle crystal to the CD surface, both in a noncovalent manner. The supramolecular particle crystals are highly robust, as witnessed by their ability to withstand agitation by ultrasonication. When assembled on a poly(dimethylsiloxane) (PDMS) stamp, the dendrimer-infiltrated particle crystals could be transfer-printed onto a CD-functionalized target surface. By variation of the geometry and size of the PDMS stamps, single particle lines, interconnected particle rings, and V-shaped particle assemblies were obtained. The particle structures served as 3D receptors for the binding of (multiple) complementary guest molecules, indicating that the supramolecular host functionalities of the particle crystals were retained throughout the fabrication process.

Ttrioctylphosphine oxide (TOPO) stabilized CdSe/ZnS quantum dots (QD) were modified with 6-ferrocenyl-1-hexanethiol (FcHT) or 11-ferrocenyl-1-undecanethiol (FcUT) via ligand exchange. The presence of ferrocenyl thiol ligands on the surface of the QDs was proven by diffusion ordered NMR spectroscopy. Upon replacement of the initial TOPO ligand with ferrocene derivatives the emission of the QDs decreased. Phase transfer of ferrocene-modified QDs from organic solvents into water was achieved by complexation reactions with beta-cyclodextrin (beta-CD). The QDs coated with ferrocene thiols are soluble in nonpolar solvents and are transferred into the aqueous phase upon formation of host-guest complexes between the ferrocene units and the cavity of beta-CD. The reversibility of the phase transfer was probed by the addition of naphthalene and adamantane derivatives to the aqueous phase containing QD-[Fc-CD] adduct.

A superhydrophobic surface with a static water contact angle (theta(w)) > 150 degrees was created by a simple "dip-coating" method of 60-nm SiO2 nanoparticles onto an amine-terminated (NH2) self-assembled monolayer (SAM) glass/silicon oxide substrate, followed by chemical vapor deposition of a fluorinated adsorbate. For comparison, a close-packed nanoparticle film, formed by convective assembly, gave theta(w) approximately 120 degrees. The stability of the superhydrophobic coating was enhanced by sintering of the nanoparticles in an O2 environment at high temperature (1100 degress C). A sliding angle of < 5 degrees indicated the self-cleaning properties of the surface. The dip-coating method can be applied to glass substrates to prepare surfaces that are superhydrophobic and transparent.

A screening method for parallel Am(3+) ligand libraries is presented. The method makes use of alpha-radiation in combination with a photographic film to detect the complexed Am(3+). After screening and development of the film spots of varying intensities are obtained. The intensities of the spots correspond with the amount of complexed Am(3+). This allows a fast discrimination between the Am(3+) complexation efficiencies of ligands from large libraries. Depending on the exposure time of the film, activities as small as 5Bq (241)Am can be detected. Using internal standards a semi-quantitative assessment can be performed.

PGMA polymer brushes are successfully grown on the inner wall of a microreactor to give a nanostructure. The oxirane groups of the brushes are used for the anchoring of a catalyst. The utility of the combination of catalyst-functionalized brushes and a microreactor is clearly demonstrated for the TBD-catalyzed Knoevenagel condensation reaction of benzaldehyde and malononitrile.

Various sulfur-modified alpha-cyclodextrin (alpha-CD) derivatives formed ordered monolayers on gold surfaces as confirmed by water contact angle goniometry, electrochemistry, X-ray photoelectron spectroscopy, and atomic force microscopy measurements. Self-assembled monolayers (SAMs) of the adsorbates showed high polarity, uniform monolayer arrangement, and low charge transfer resistance. Electrochemical capacitance measurements were used to determine the binding affinity of aliphatic carboxylic acid salts with four, six, and eight carbon atoms. The nonmethylated cyclodextrin host-guest pairs showed 1-2 orders of magnitude higher binding constants on surfaces than in solution.

Porous stamps fabricated by one-step phase separation micromolding were used for microcontact printing of polar inks, in particular aqueous solutions of dendrimers, proteins, and nanoparticles. Permanent hydrophilicity was achieved without any additional treatment by tailored choice of the polymer components. Pores with several hundred nanometers to micrometers were obtained during the phase separation process. These pores can act as ink reservoirs. The porous stamps were thoroughly characterized by SEM, NMR, and contact angle measurement. The versatility of the porous stamps was shown in three printing schemes. First, positive microcontact printing was achieved by printing a polar thioether-modified dendrimer as the ink, followed by backfilling and wet etching. Second, the porous stamps were used for multiple printing of fluorescent proteins without reinking. Third, nanoparticles of about 60 nm in diameter, which cannot be directly transferred by oxidized PDMS stamps, were successfully printed onto substrates by using these porous stamps.

The formation of stable and ordered free-standing porous supramolecular assemblies of nanoparticles with sizes and geometries controlled at different length scales is demonstrated by a double-templating strategy. Our technique combines the directed assembly of particles, templating using nanoimprint lithography (NIL), and supramolecular layer-by-layer (LbL) assembly. First, 500-nm beta-cyclodextrin (CD)-functionalized polystyrene (PS) particles were assembled by convective assembly onto a sacrificial polymer template patterned with a predefined geometry and size using NIL, forming a 3D crystal architecture of particles. LbL assembly of alternating supramolecular host- and guest-functionalized glues of CD-functionalized Au (Au-CD) nanoparticles and adamantyl (Ad) dendrimers, sized between 3-5 nm, within the preformed PS-particle crystal effectively bound the particles together into a particle composite. These particle composites were released from the substrate together with the polymer template, and transferred onto a target substrate. The particle crystal integrity, order and functionality were preserved. Rinsing the structure with dichloromethane removed the PS core material together with the polymer template, resulting in interconnected porous capsules, the sizes and shapes of which are fully determined by the PS core size and the polymer template definition. Again, integrity and shape were preserved in the rinsing step. These capsules were capable of storing organic fluorescent molecules using specific interactions.

A novel inverse imprinting procedure for nanolithography is presented which offers a transfer accuracy and feature definition that is comparable to state-of-the-art nanofabrication techniques. We illustrate the fabrication quality of a demanding nanophotonic structure: a photonic crystal waveguide. Local examination using photon scanning tunneling microscopy (PSTM) shows that the resulting nanophotonic structures have excellent guiding properties at wavelengths in the telecommunications range, which indicates a high quality of the local structure and the overall periodicity.

Fluorescent self-assembled monolayers (SAMs) are used as dip-pen nanolithography (DPN) substrates for the fabrication of patterns of Ca(2+) and Cu(2+) ions. The driving force for the transfer of these ions from an atomic force microscopy (AFM) tip to the surface is their complexation to organic ligands on the monolayer. By means of fluorescent surfaces, the patterns can be visualized under a fluorescence microscope. We use a custom-built atomic force fluorescence microscope (AFFM), a combination of atomic force and confocal fluorescence microscopes, to deposit the metal ions onto the sensing SAMs by DPN and to subsequently visualize modulations of fluorescence intensity in a sequential write-read mode.

Superhydrophobic surfaces in Wenzel and metastable wetting state were prepared and the conversion of such surfaces to ultraphobic surfaces was reported by the application of a fine-scale roughness. Silicon nitride substrates with hexagonally arranged pillars were prepared by micromachining. The two-scale roughness was achieved by coating these substrates with 60 nm silica nanoparticles. The surface was made hydrophobic by silanization with octadecytrichlorosilane (OTS). Wettability studies of the silicon nitride flat surface, silicon nitride pillars, and the surfaces with two-scale roughness showed that a two-scale roughness can effectively improve the hydrophobicity of surfaces with a higher apparent contact angle and reduced contact angle hysteresis when the original rough surface was in a metastable or Wenzel state. This study shows the pathway of converting a metastable hydrophobic surface to an ultraphobic surface by the introduction of a fine-scale roughness, which adds to the literature a new aspect of fine-scale roughness effect.

The assembly of complex bionanostructures onto beta-cyclodextrin (betaCD) monolayers has been investigated with the aims of antibody recognition and cell adhesion. The formation of these assemblies relies on host-guest, protein-ligand, and protein-protein interactions. The buildup of a structure consisting of a divalent bis(adamantyl)-biotin linker, streptavidin (SAv), biotinylated protein A (bt-PA), and an Fc fragment of a human immunoglobin G (IgG-Fc) was studied with surface plasmon resonance (SPR) spectroscopy. Patterns of this bionanostructure were obtained via microcontact printing of the divalent linker at the molecular printboard, followed by the subsequent attachment of the proteins. Fluorescence microscopy showed that the buildup of these bionanostructures on the betaCD monolayers is highly specific. On the basis of these results, bionanostructures were made in which whole antibodies (ABs) were used instead of the IgG-Fc. These ABs were bound to the SAv layer via biotinylated protein G (bt-PG) or via a biotinylated AB. These constructions yielded specifically bound ABs with a less than maximal density, as shown by SPR spectroscopy and atomic force microscopy (AFM). Finally, the immobilization of ABs to the molecular printboard was used to create platforms for lymphocyte cell count purposes. Monoclonal ABs (MABs) were attached to the SAv layer using bt-PG, an engineered biotin functionality, or through nonspecific adsorption. The binding specificity of the immobilized cells was the highest on the buildup made from bt-PG, which is attributed to an optimized orientation of the antibodies. An approximately linear relationship between the numbers of seeded cells and counted cells was demonstrated, rendering the platform potentially suitable for lymphocyte cell counting.

Here, the stepwise assembly of an electroactive bionanostructure on a molecular printboard is described. The system consists of a cyclodextrin receptor monolayer (molecular printboard) on glass, a divalent linker, streptavidin (SAv), and biotinylated cytochrome c (cyt c). The divalent linker consists of a biotin moiety for binding to SAv and two adamantyl moieties for supramolecular host-guest interaction at the cyclodextrin molecular printboard. The binding of biotinylated cyt c onto a SAv layer bound to preadsorbed linker appeared to be highly specific. The coverages of cyt c as assessed by UV-vis spectroscopy and scanning electrochemical microscopy (SECM) appeared to be identical indicating that all cyt c units remained active. Moreover, the coverage values corresponded well with an estimate based on steric requirements, and the binding stoichiometry was therefore found to be by two biotin moieties of cyt c per one SAv molecule.

A novel method for the efficient discovery of new types of minor actinide (MA) ligands is based on the unique combination of "tea bag" split pool combinatorial chemistry and screening based on the inherent radioactivity of the complexed cations. Four multicoordinating Am(3+) chelating groups, such as CMPO (diphenylcarbamoylmethyl)phosphine oxide), PICO (picolinamide), DGA (N,N'-dimethyldiglycoldiamide), and MPMA (N-methyl-N-phenylmalonamide), on a trityl platform immobilized on TentaGelS served as a model library for the development of the screening method. This model library was screened under various conditions (i.e., 0.001 M < or = [HNO3] < or = 3 M, NaNO3 < or = 4 M, and [Eu] < or = 10 x [ligand]) showing competitive extraction of the four ligands. Other libraries of 9 and 72 members were synthesized by functionalization of the trityl platform with ligating groups that are composed of four building blocks (including at least one amide and one (phosphoric) hydrazone moiety). The screening of these two libraries resulted in the discovery of two multicoordinate ligands that contain ligating groups previously not known to complex Am(3+). Both are N-isopropyl amides terminated with a p-methoxyphenyl hydrazide (A2B1C1D10 K(D(Am)) = 2197) or a p-nitrophenyl hydrazide (A2B1C1D11 K(D(Am)) =1989) moiety, respectively. They are more efficient than the immobilized tritylCMPO ligand (K(D(Am)) = 1280) at 3 M HNO3. This method has the advantages of a high analytical sensitivity and the direct comparison of the extraction results. The method also allows the competitive screening of multiple nuclides which can be quantified by their radioactive emission spectrum.

Different methods to create chemically patterned, flat PDMS stamps with two different chemical functionalities were compared. The best method for making such stamps, functionalized with 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFDTS) and 3-(aminopropyl)triethoxysilane (APTS), appeared to be full functionalization of a freshly oxidized flat PDMS stamp with either adsorbate, followed by renewed oxidation through a mask and attachment of the other adsorbate. These stamps were used to transfer polar inks (a thioether-functionalized dendrimer and a fluorescent dye) by microcontact printing. The PFDTS monolayer was used as a barrier against ink transfer, while the APTS SAM areas functioned as an ink reservoir for polar inks. The printing results confirmed the excellent transfer of hydrophilic inks with these stamps to gold and glass substrates, even from aqueous solutions. Attachment of a fluorescent dye on the amino-functionalized regions shows the possibility of the further modification of the chemically patterned stamps for tailoring of the stamps' properties.

The supramolecular layer-by-layer assembly of 3D multicomponent nanostructures of nanoparticles is demonstrated. Nanoimprint lithography (NIL) was used as the patterning tool for making patterned beta-cyclodextrin (CD) self-assembled monolayers (SAMs) and for the confinement of nanoparticles on the substrate. A densely packed and multilayered nanoparticle structure was created by alternating assembly steps of complementary guest- (Fc-SiO(2), 60 nm) and host-functionalized (CD-Au, 3 nm) nanoparticles. The effects induced by the order of the nanoparticle assembly steps, going from large to small and from small to large nanoparticles by using Fc-SiO(2), CD-Au, and CD-SiO(2) (350 nm) nanoparticles, were compared. AFM height profiles revealed that the specific supramolecular assembly of nanoparticles was self-limited, i.e. one nanoparticle layer per assembly step, allowing the control over the thickness of the supramolecular hybrid nanostructure by choosing the size of the nanoparticles, irrespective of the core material of the nanoparticles. The roughness of structure, observed by AFM imaging of the top layer, was directly influenced by the size and packing of the underlying nanoparticle layers.