Nonlinear AFM dynamics: Despite its importance in many nanomanipulation experiments, most intermittent contact atomic force microscopes do not monitor the nonlinear response of the oscillating cantilever. A recent study provides an effective strategy for measuring and analyzing these nonlinear tip–sample dynamics (see figure). Interestingly, distinct nonlinear regimes are identified – including a chaotic mode – at small tip–sample spacings.

Trading places: Bifunctional thiol ligands were immobilized onto positively charged silica gel and onto Rink resin through electrostatic interactions. The image shows the place-exchange reaction between the alkanethiolate-protected gold nanoparticles and the polymer-bound bifunctional thiol ligands; monocarboxyl gold nanoparticles were obtained as the major product, cleaved off from the polymer support under mild conditions.

Site-selective integration of a nanoparticle assembly on a surface monolayer template was achieved by penetration of solvents followed by selective lift-off of nanoporous granular films. Either positive or negative patterns on the substrate could be fabricated by appropriate selection of solvents used for washing (see figure), thus providing an effective methodology for desirable integration of various monolayer-protected inorganic nanoparticles through simple solution-based processing.

Making biosense: Electroactive poly(guanine)-functionalized silica nanoparticles have been synthesized and used as biological labels (see scheme). An electrochemical immunobiosensor based on such labels was developed, which utilizes a mediator-generated catalytic reaction. This immunobiosensor is very sensitive for IgG detection (to a limit of 0.2 ng mL⁻¹ or 1.3 pM), which was attributed to signal amplification from the poly(guanine)-functionalized silica nanoparticles and from the catalytic oxidation of guanine.

Targeting proteins: Metal phosphate nanoparticles (see scheme; NHS-biotin=biotinamidohexanoyl-6-amino-hexanoic acid N-hydroxy-succinimide ester) based on an apoferritin template have been synthesized and used as biological labels for electrochemical immunoassay. The template offers a simple and convenient route for the preparation of metallic nanoparticle labels under mild conditions. The assay method is ultrasensitive (detection limit as low as 77 fm); simultaneous detection of multiple protein targets can be performed by using different labels.

Sensor sensibility: A sensor that continuously monitors levels of analytes by emitting a radiofrequency signal could be used to determine metabolite or drug levels in vivo. We describe a sensor that consists of a semipermeable membrane, magnetic nanoparticles, and a binding protein that responds to analyte with reversible changes in the size of nanoparticle/binding protein microaggregates, which changes sensor proton relaxation times (see figure).

Ferritin about for Ti: The cage-shaped protein supramolecule apoferritin is genetically modified to have Ti-specific affinity peptides outside its protein shell (minT1-LF). Mobile peptides bestow a strong adsorption force to a Ti surface and the placement of minT1-LF with ferrihydrite or Co₃O₄ nanoparticles onto nanometric Ti patterns is experimentally demonstrated. This biological method opens up a new pathway to nanoparticle placement (the picture shows minT1-LF; four subunits are removed to show the NP core).

Wired for high performance: The role of relative surface area in Si nanowire (NW) transistor (see image) performance was examined by comparing the performance of microwire (μW) field-effect transistors (FETs) fabricated side-by-side with NW FETs. Both n- and p-type NW FETs were found to be more sensitive to surface states than their μW counterparts; these results are utilized to produce NW n-FETs with consistent performance.

The toxicity of CdSe nanoparticles is mediated by metallothioneins (MTs), which are ubiquitous and cysteine-rich. Surface Cd²⁺ ions are depleted from thiocarboxylate-capped CdSe nanoparticles by recombinant MT-based peptides (see figure), while surface Zn²⁺ ion depletion from ZnS-coated CdSe nanoparticles is more difficult. Due to the overall cellular expression and antioxidant roles for MT, a model for MT-mediated CdSe nanoparticle toxicity is proposed.

Easy does it: Poly(3,4-ethylenedioxythiophene) (PEDOT) fibers can be synthesized from aqueous solutions of anionic surfactant by a self-assembly method. This approach readily generates nanofibers with diameters down to about 10 nm and lengths of over 5 μm (see TEM image). The fibers can be produced with high yields and exhibit electrical conductivities of approximately 46 S cm⁻¹.

When the chips are down: A stable zeolite nanocrystal matrix accommodating trypsin has been constructed on a microfluidic chip as a bioreactor to favor highly efficient proteolysis (see picture). The whole procedure is rapid and easily manipulated, thus providing a promising way to solve low-efficiency digestion in advancing the development of proteomics. PMMA=poly(methyl methacrylate).

The worm turns: Carbon nanotubes (CNTs) are encapsulated within predesigned, wormlike, hollow silica capsules (see image). The preparation strategy comprises a two-step process; silica coating of the CNTs is followed by selective dissolution from the inside out. The silica coating involves the initial deposition of a thinner shell at low pH values, followed by the growth of an outer shell at higher pH values, with a controlled thickness that determines the final outer diameter of the capsule.

CdS nanoparticles (NPs) functionalized with nucleotides were used to assemble layered NP arrays stabilized by H bonds (see scheme). The association of various nucleotides between the NPs and electrode, with subsequent sequential nucleotide linkages, allows control of the number of layers. The nucleotide-crosslinked CdS NP assemblies reveal photoelectrochemical activities; the intensity of the photocurrent increases with number of NP layers.

Growing against the grain: Hierarchically structured ZnO nanowires are generated from an aqueous solution containing an organic molecule (see figure). The oriented architecture of nanograins leads to the formation of nanowires with incorporated organic molecules. The sulfonate groups in the organic molecules are important for the emergence of hierarchical nanowires, especially for the complexation to zinc precursor species and the interaction between zinc oxide crystals.

Melt down! A meltable, amphiphilic carbon nanotube derivative was obtained in a two-step functionalization process whereby oxidation of the nanotube was followed by a surface reaction with a polyethylene glycol-substituted tertiary amine. The derivative underwent a reversible solid-to-liquid transition at 35 °C (see image) and was highly dispersible in both aqueous and organic media.

Streptavidin (SAv) is attached to β-cyclodextrin (β-CD) self-assembled monolayers (SAMs) via orthogonal β-CD host–guest and SAv–biotin interactions. Various assembly schemes are allowed through the use of orthogonal linkers, and the valency of the linkers offers control over the binding affinity. Most versatile is the stepwise assembly at the β-CD SAM as shown by heterofunctionalization of the SAv binding pockets (see scheme).

Pores for effects: WO₃ thin films with nanometer-scale periodicity and a highly crystalline framework were obtained by sol-gel templating using suitable templates and appropriate preparation conditions. These materials revealed an improved electrochemical/electrochromic performance (in terms of response times, cycling stability, etc.) due to the favorable combination of 3D mesoporosity and crystallinity.

Turning a corner: The growth behavior and optimality of fungal space-searching algorithms in microfluidic mazes and networks has been evaluated. It was found that fungal growth behavior was strongly modulated by the geometry of microconfinement (see image; numbers show time in minutes). The fungus used a complex growth and space-searching strategy comprising two algorithmic subsets. This study suggests that even simple microorganisms have developed adequate strategies to solve nontrivial geometrical problems.