A direct-write "dip-pen" nanolithography (DPN) has been developed to deliver collections of molecules in a positive printing mode. An atomic force microscope (AFM) tip is used to write alkanethiols with 30-nanometer linewidth resolution on a gold thin film in a manner analogous to that of a dip pen. Molecules are delivered from the AFM tip to a solid substrate of interest via capillary transport, making DPN a potentially useful tool for creating and functionalizing nanoscale devices.

Data from ab-oriented YBa 2 Cu 3 O 7 ͞I͞Cu tunnel junctions are presented. Self-assembled monolayers form the insulating tunnel barrier, I. The YBa 2 Cu 3 O 7 features in the tunneling conductance match those of low-leakage ab-oriented YBa 2 Cu 3 O 7 ͞Pb junctions. Results show that the zero-bias conductance peak is an Andreev bound state (ABS) of a d-wave order parameter. In zero magnetic field, the ABS splits below ϳ7 K, consistent with the presence of a subdominant order parameter at the surface. An applied magnetic field induces further splitting that grows nonlinearly with increasing field.[S0031-9007 (97)03529-1] PACS numbers: 74.50. + r, 74.72.Bk

G-quadruplex (G4) with stacked G-tetrads structure is able to bind hemin (iron (III)-protoporphyrin IX) to form a unique type of DNAzyme/RNAzyme with peroxidase-mimicking activity, which has been widely employed in multidisciplinary fields. However, its further applications are hampered by its relatively weak activity compared with protein enzymes. Herein, we report a unique intramolecular enhancement effect of the adjacent adenine (EnEAA) at 3′ end of G4 core sequences that significantly improves the activity of G4 DNAzymes. Through detailed investigations of the EnEAA, the added 3′ adenine was proved to accelerate the compound I formation in catalytic cycle and thus improve the G4 DNAzyme activity. EnEAA was found to be highly dependent on the unprotonated state of the N1 of adenine, substantiating that adenine might function as a general acid–base catalyst. Further adenine analogs analysis supported that both N1 and exocyclic 6-amino groups in adenine played key role in the catalysis. Moreover, we proved that EnEAA was generally applicable for various parallel G-quadruplex structures and even G4 RNAzyme. Our studies implied that adenine might act analogously as the distal histidine in protein peroxidases, which shed light on the fundamental understanding and rational design of G4 DNAzyme/RNAzyme catalysts with enhanced functions.

Single-walled carbon nanotubes (SWNTs) with high covalent bonding density of polymer layers have been prepared by a "grafting to" approach, where the benzyl chloride groups of styrene copolymers (M n ) 47 600) reacted with the alkyne groups on SWNTs under relatively mild conditions, resulting in a higher grafting efficiency, as high as 81 wt % of (TGA). Microscopic observations clearly displayed the uniform, thick polymer layers formed on the SWNT surface. The high density of covalent bonding between polymer and nanotubes was confirmed by Raman, 1 H NMR, and FTIR, which makes them well dissolved in organic solvents and homogeneously dispersed in polymer matrices. The in situ UV-vis observations during the dissolution indicated that for such a multifunctional system almost no cross-links occurred between SWNTs due to the physical absorption and steric hindrance of polymer chains during the functionalization of SWNTs. The functionalized SWNTs exhibited a pronounced effect on the mechanical properties of polystyrene composites. Only 0.06 wt % of SWNTs resulted in 82% and 78% of increases in tensile strength and elastic modulus of the composites, respectively, indicating an efficient interfacial stress transfer between SWNTs and polymer.

Novel well-defined redox-responsive ferrocene-containing amphiphilic block copolymers (PACMO-b-PAEFC) were synthesized by ATRP, with poly(N-acryloylmorpholine) (PACMO) as hydrophilic blocks and poly(2-acryloyloxyethyl ferrocenecarboxylate) (PAEFC) as hydrophobic blocks. The copolymers were characterized by FT-IR and H NMR spectroscopies and gel permeation chromatography, and the crystalline behavior was determined by X-ray diffraction and small-angle X-ray scattering. The results showed that the size of the lamellar crystals and crystallinity vary with the systematic compositions while the periodic structure of the lamellar stacks has no obvious change. These block copolymers could self-assemble and form globular nanoscaled core-shell micellar aggregates in aqueous solution. The reductive ferrocene groups could be changed into hydrophilic ferrocenium via mild oxidation, whereas the polymer micelles at the oxidation state could reversibly recover from their original states upon reduction by vitamin C. The tunable redox response was investigated and verified by transmission electron microscopy, ultraviolet-visible spectroscopy, cyclic voltammetry, and dynamic light scattering measurements. The copolymer micelles were used to entrap anticancer drug paclitaxel (PTX), with high drug encapsulation efficiency of 61.4%, while the PTX-loaded drug formulation exhibited oxidation-controlled drug release, and the release rate could be mediated by the kinds and concentrations of oxidants. MTT assay was performed to disclose the biocompatibility and security of the copolymer micelles and to assess anticancer efficiency of the PTX-loaded nanomicelles. The developed copolymer nanomicelles with reversible redox response are anticipated to have potential in targeted drug delivery systems for cancer therapy.