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Uniform size of Si nanowires (NWs) is highly desirable to enhance the performance of Si NW-based lithium-ion batteries. To achieve a narrow size distribution of Si NWs, the formation of bulk-like Si structures such as islands and chunks needs to be inhibited during nucleation and growth of Si NWs. We developed a simple approach to control the nucleation of Si NWs

Hierarchical architectures composed of nanomaterials in different forms are essential to improve the performance of lithium-ion battery (LIB) anodes. Here, we systematically studied the effects of hierarchical ZnO nanostructures on the electrochemical performance of LIBs. ZnO nanowire (NW) trunks were decorated with ZnO NWs or ZnO nanosheets (NSs) by successive hydrothermal synthesis to create hierarchical three-dimensional nanostructures. The branched ZnO NSs on the ZnO NW trunk exhibited a two-fold higher specific gravimetric capacity compared to ZnO NWs and branched ZnO NWs on ZnO NW trunks after 100 cycles of charging–discharging at 0.2C (197.4 mA g−1). The improvement in battery anode performance is attributable to the increased interfacial area between the electrodes and electrolyte, and the void space of the branched NSs that facilitates lithium ion transport and volume changes during cycling.

We show that olefin metathesis can be used in an extremely simple process to rapidly alter the morphology of self-assembled poly(butadiene-b-ethylene oxide) (PB–PEO) dispersions in situ. The addition of a water-insoluble Hoveyda–Grubbs catalyst to aqueous assemblies of PB–PEO leads to degradation of the hydrophobic PB block by well-established metathesis pathways and a concomitant change in the composition of the block copolymer. This phenomenon drives morphological transitions characterized by rapidly decreasing sizes of the self-assembled aggregates, the ultimate extent of which is readily controlled by catalyst concentration. Exemplary cases are presented in which transitions from worm-like micelles to spherical micelles or from vesicles to worm-like micelles can be accomplished within minutes.

We investigated the formation of hybrid lipid/polymer (1,2-dioleoyl-sn-glycero-3-phosphocholine and poly(ethylene oxide-b-butadiene); DOPC/EO22Bd37) films onto planar silica surfaces. Using laser scanning confocal microscopy, atomic force microscopy, and quartz crystal microbalance analysis, we monitored the adsorption and fusion of hybrid lipid/polymer vesicles onto planar borosilicate glass cleaned via chemical etching or RF/air plasma treatment. In addition we used cryo-electron microscopy to characterize film formation on mesoporous silica nanoparticles. As the polymer content in the vesicles increased, the resulting hybrid lipid/polymer films on borosilicate glass - cleaned by chemical etching or plasma treatment - were more heterogeneous, indicating a large number of adsorbed vesicles rather than continuous bilayer films at higher polymer loadings. The observed lateral fluidity of both DOPC and hybrid lipid/polymer films also decreased substantially with increasing polymer fraction and was found to be relatively insensitive to changes in pH. Films prepared from vesicles with higher polymer loadings were completely immobile. We also found that polymer vesicles did not interact with clean plasma-treated glass surfaces, which may be due to elevated OH and Si-OH on plasma-treated surfaces. Conformal hybrid lipid/polymer coatings consistent with bilayers could be formed on mesoporous silica nanoparticles and imaged via cryo-electron microscopy. These results expand the library of biocompatible materials that can be used for coating silica-based materials and nanoparticles.

Controlling the traffic of molecules and ions across membranes is a critical feature in a number of biologically relevant processes and highly desirable for the development of technologies based on membrane materials. In this paper, ion transport behavior of hybrid lipid/polymer membranes was studied in the absence and presence of ion transfer agents. A pH-sensitive fluorophore was used to investigate ion (H + /OH − ) permeability across hybrid lipid/polymer membranes as a function of the fraction of amphiphilic block copolymer. It was observed that vesicles with intermediate lipid/polymer ratios tend to be surprisingly more permeable to ion transport than the pure lipid or pure polymer vesicles. Hybrid vesicle permeability could be further modulated with valinomycin, nigericin, or gramicidin A, which significantly expedite the dissipation of externally-imposed pH gradients by facilitating the transport of the rate-limiting co-ions ( e.g. K + ) ions across the membrane. For gramicidin A, ion permeability decreased with increasing polymer mole fraction, and the method of introduction of gramicidin A into the membrane played an important role. Strategies to incorporate biofunctional molecules and facilitate their activity in synthetic systems are highly desirable for developing artificial organelles or other synthetic compartmentalized structures requiring control over molecular traffic across biomimetic membranes.

We herein describe the development of a single-walled carbon nanotube (SWNT)-based electrical biosensor consisting of a two-terminal resistor, and report its use for the specific, label-free detection of pathogenic bacteria via changes in conductance. The ability of this biosensor to recognize different pathogenic bacteria was analyzed, and conditions were optimized with different probe concentrations. Using this system, the reference strains and clinical isolates of Staphylococcus aureus and Escherichia coli were successfully detected; in both cases, the sensor showed a detection limit of 10 CFU. This SWNT-based electrical biosensor will prove useful for the development of highly sensitive and specific handheld pathogen detectors.

In spite of having several advantages such as low cost, high chemical stability, and environmentally safe and benign synthetic as well as operational procedures, the full potential of carbon dots (CDs) is yet to be explored as photosensitizers due to the challenges associated with the fabrication of well-arrayed CDs with many other photocatalytic heterostructures. In the present study, a unique combination of metal-organic framework (MOF)-decorated zinc oxide (ZnO) 1D nanostructures as host and CDs as guest species are explored on account of their potential application in photoelectrochemical (PEC) water splitting performance. The synthetic strategy to incorporate well-defined nitrogen-doped carbon dots (N-CDs) arrays onto a zeolitic imidazolate framework-8 (ZIF-8) anchored on ZnO 1D nanostructures allows a facile unification of different components which subsequently plays a decisive role in improving the material's PEC water splitting performance. Simple extension of such strategies is expected to offer significant advantages for the preparation of CD-based heterostructures for photo(electro)catalytics and other related applications.

Amphiphilic gold nanoparticles (AuNPs) functionalized with mixed monolayers consisting of hydrophobic and hydrophilic ligands find widespread applications in biosensing, drug delivery, and bioimaging. One important aspect of amphiphilic AuNPs in such applications is the tuning of the surface properties of these AuNPs by modifying the composition of the ligands. In this study, well-dispersed AuNPs as individuals with mixed monolayers of hydrophobic and hydrophilic ligands were synthesized and the ratios of hydrophilic and hydrophobic ligands on the AuNP surfaces with varying ligand lengths were investigated by electrostatic titration. We demonstrated that longer hydrophobic ligands have higher affinity for the AuNP surface, and that the relative ligand length plays an important role in determining the maximum hydrophobic coverage on the AuNP surface at which the ratio of the amount of hydrophobic to that of hydrophilic ligands on the AuNP surface is the largest, for AuNPs to remain as individuals. We expect that the AuNPs synthesized with diverse ratios of hydrophobic and hydrophilic ligands on the surface can be useful in biological applications.

Self-assembled giant polymer vesicles prepared from double-hydrophilic diblock copolymers, poly(ethylene oxide)-b-poly(acrylic acid) (PEO-PAA) show significant degradation in response to pH changes. Because of the switching behavior of the diblock copolymers at biologically-relevant pH environments (2 to 9), these polymer vesicles have potential biomedical applications as smart delivery vehicles.

Molecular amphiphiles self-assemble in polar media to form ordered structures such as micelles and vesicles essential to a broad range of industrial and biological processes. Some of these architectures such as bilayer sheets, helical ribbons, and hollow tubules are potentially useful but inherently unstable owing to the presence of open edges that expose the hydrophobic bilayer core. Here, we describe a strategy to stabilize open bilayer structures using amphiphilic nanoparticle surfactants that present mixtures of hydrophilic and hydrophobic ligands on their surface. We observe that these particles bind selectively to the open edge of bilayer membranes to stabilize otherwise transient amphiphile assemblies. We show how such particles can precisely control the size of lipid tubules, how they can inhibit the formation of undesirable assemblies such as gallstone precursors, and how they can stabilize free-floating lipid microdiscs.

We describe the spontaneous incorporation of amphiphilic gold nanoparticles (Au NPs) into the walls of surfactant vesicles. Au NPs were functionalized with mixed monolayers of hydrophilic (deprotonated mercaptoundecanoic acid, MUA) and hydrophobic (octadecanethiol, ODT) ligands, which are known to redistribute dynamically on the NP surface in response to changes in the local environment. When Au NPs are mixed with preformed surfactant vesicles, the hydrophobic ODT ligands on the NP surface interact favorably with the hydrophobic core of the bilayer structure and guide the incorporation of NPs into the vesicle walls. Unlike previous strategies based on small hydrophobic NPs, the present approach allows for the incorporation of water-soluble particles even when the size of the particles greatly exceeds the bilayer thickness. The strategy described here based on inorganic NPs functionalized with two labile ligands should in principle be applicable to other nanoparticle materials and bilayer structures.

A simple and reliable method is described to produce inorganic nanoparticles functionalized asymmetrically with domains of hydrophobic and hydrophilic ligands on their respective hemispheres. These amphiphilic, Janus-type particles form spontaneously by a thermodynamically controlled process, in which the particle cores and two competing ligands assemble at the interface between two immiscible liquids to reduce the interfacial energy. The asymmetric surface chemistry resulting from this process was confirmed using contact angle measurements of water droplets on nanoparticle monolayers deposited onto hydrophobic and hydrophilic substrates-particles presenting their hydrophobic face give contact angles of ∼96°, those presenting their hydrophilic face ∼19°. The spontaneous assembly process is rationalized by a thermodynamic model, which accounts both for the energetic contributions driving the assembly and for the entropic penalties that must be overcome. Consistent with the model, amphiphilic NPs form only when there is sufficient interfacial area to accommodate them; however, this potential limitation is easily overcome by mechanical agitation of the two-phase mixture. While it is straightforward to vary the ratio of hydrophobic and hydrophilic ligands, the accumulation of amphiphilic particles at the interface is maximal for ligand ratios near 1:1. In addition to gold nanoparticles and thiolate ligands, we demonstrate the generality of this approach by extending it to the preparation of amphiphilic iron oxide nanoparticles using two types of diol-terminated ligands. Depending on the material properties of the inorganic cores, the resulting amphiphilic particles should find applications as responsive particle surfactants that respond dynamically to optical (plasmonic particles) and/or magnetic (magnetic particles) fields.

We investigate the self-assembly of amphiphilic nanoparticles (NPs) functionalized with mixed monolayers of hydrophobic and hydrophilic ligands in water. Unlike typical amphiphilic particles with "fixed" surface chemistries, the ligands used here are not bound irreversibly but can rearrange dynamically on the particles' surface during their assembly from solution. Depending on the assembly conditions, these adaptive amphiphiles form compact micellar clusters or extended chain-like assemblies in aqueous solution. By controlling the amount of hydrophobic ligands on the particles' surface, the average number of nearest neighbors--that is, the preferred coordination number--can be varied systematically from ∼ 1 (dimers) to ∼ 2 (linear chains) to ∼ 3 (extended clusters). To explain these experimental findings, we present an assembly mechanism in which hydrophobic ligands organize dynamically to form discrete patches between proximal NPs to minimize contact with their aqueous surroundings. Monte Carlo simulations incorporating these adaptive hydrophobic interactions reproduce the three-dimensional assemblies observed in experiment. These results suggest a general strategy based on reconfigurable "sticky" patches that may allow for tunable control over particle coordination number within self-assembled structures.