Chiral assemblies of nanoparticles (NPs) are typically constructed with helical or tetrahedral geometries. Simple pairs of NPs are not expected to display chirality due to basic symmetry ...considerations made under the assumption of their spherical geometry. In this study we demonstrate that assemblies consisting of two metallic NPs do possess chirality and strongly rotate polarization of light. Their chiroplasmonic properties are attributed to the prolate geometry of individual colloidal particles. When bridged by biomolecules, the NP pairs acquire scissor-like geometry, with the long axes of NPs forming an angle of ∼9°. This small dihedral angle results in chirality of the NP pair, while the consistency of its sign due to the specific conformation of the bridging biomacromolecules breaks the enantiomeric equivalence of the NP pairs. Strong polarization rotation in these nanoassemblies makes possible their utilization in biological analysis. Heterodimers of gold and silver NPs were made using antibody–antigen bridges. Taking advantage of their chiroplasmonic properties, we investigated their bioanalitical potential for detection of an environmental toxin, microcystin-LR, and a cancer biomarker, prostate-specific antigen. The order-of-magnitude improvements in limits of detection compared to all other analytical techniques are attributed to plasmonic enhancement of intrinsic chirality of biological compounds, strong optical coupling of photons with NP assemblies with twisted geometries, and signal amplification due to the bisignate nature of circular dichroism bands.
Nanoscale plasmonic assemblies display exceptionally strong chiral optical activity. So far, their structural design was primarily driven by challenges related to metamaterials whose practical ...applications are remote. Here we demonstrate that gold nanorods assembled by the polymerase chain reaction into DNA-bridged chiral systems have promising analytical applications. The chiroplasmonic activity of side-by-side assembled patterns is attributed to a 7-9 degree twist between the nanorod axes. This results in a strong polarization rotation that matches theoretical expectations. The amplitude of the bisignate 'wave' in the circular dichroism spectra of side-by-side assemblies demonstrates excellent linearity with the amount of target DNA. The limit of detection for DNA using side-by-side assemblies is as low as 3.7 aM. This chiroplasmonic method may be particularly useful for biological analytes larger than 2-5 nm which are difficult to detect by methods based on plasmon coupling and 'hot spots'. Circular polarization increases for inter-nanorod gaps between 2 and 20 nm when plasmonic coupling rapidly decreases. Reaching the attomolar limit of detection for simple and reliable bioanalysis of oligonucleotides may have a crucial role in DNA biomarker detection for early diagnostics of different diseases, forensics and environmental monitoring.
The structural complexity of composite biomaterials and biomineralized particles arises from the hierarchical ordering of inorganic building blocks over multiple scales. Although empirical ...observations of complex nanoassemblies are abundant, the physicochemical mechanisms leading to their geometrical complexity are still puzzling, especially for nonuniformly sized components. We report the self-assembly of hierarchically organized particles (HOPs) from polydisperse gold thiolate nanoplatelets with cysteine surface ligands. Graph theory methods indicate that these HOPs, which feature twisted spikes and other morphologies, display higher complexity than their biological counterparts. Their intricate organization emerges from competing chirality-dependent assembly restrictions that render assembly pathways primarily dependent on nanoparticle symmetry rather than size. These findings and HOP phase diagrams open a pathway to a large family of colloids with complex architectures and unusual chiroptical and chemical properties.
Harvesting osmotic energy from industrial wastewater is an often‐overlooked source of electricity that can be used as a part of the comprehensive distributed energy systems. However, this concept ...requires, a new generation of inexpensive ion‐selective membranes that must withstand harsh chemical conditions with both high/low pH, have high temperature resilience, display exceptional mechanical properties, and support high ionic conductance. Here, aramid nanofibers (ANFs) based membranes with high chemical/thermal stability, mechanical strength, toughness, and surface charge density make them capable of high‐performance osmotic energy harvesting from pH gradients generated upon wastewater dilution. ANF membranes produce an averaged output power density of 17.3 W m−2 for more than 240 h at pH 0. Taking advantage of the high temperature resilience of aramid, the output power density is increased further to 77 W m−2 at 70 °C, typical for industrial wastewater. Such output power performance is 10× better compared to the current state‐of‐the‐art membranes being augmented by Kevlar‐like environmental robustness of ANF membranes. The improved efficiency of energy harvesting is ascribed to the high proton selectivity of ANFs. Retaining high output power density for large membrane area and fluoride‐free synthesis of ANFs from recyclable material opens the door for scalable wastewater energy harvesting.
Aramid nanofibers (ANFs) based membranes with high chemical/thermal stability, mechanical strength, toughness, and surface charge density make them capable of high‐performance osmotic energy harvesting from pH gradients generated upon wastewater dilution. Such output concentration energy power performance of ANFs membrane is 10× better compared to the current state‐of‐the‐art membranes, which is ascribed to the high proton selectivity.
When carbon fibres just won't do, but nanotubes are too expensive, cost-conscious materials scientists need a practical conductive composite. The answer could lie with graphene sheets.
The effect of chemical-composition modification on the chiroptical property of chiral organic ammonium cation-containing organic inorganic hybrid perovskite (chiral OIHP) is investigated. Varying the ...mixing ratio of bromide and iodide anions in S- or R-C6H5CH2(CH3)NH3)2PbI4(1–x)Br4x modifies the band gap of chiral OIHP, leading to a shift of the circular dichroism (CD) signal from 495 to 474 nm. However, it is also found that an abrupt crystalline structure transition occurs, and the CD signal is turned off when iodide-determinant phases are transformed into the bromide-determinant phase. To obtain CD in the wavelength range where the bromide-determinant phase is supposed to exhibit chiroptical activity, that is, <474 nm, S- or R-C12H7CH2(CH3)NH3 with a larger spacer group can be adopted; thus, the CD signal can be further blue-shifted to ∼375 nm. Here, we show that chemical-composition modification of chiral OIHP affects the chiroptical properties of chiral OIHP in two ways: (1) tuning the wavelength of CD by modulating the excitonic band structure and (2) switching the CD on and off by inducing a crystalline-structure change. These properties can be utilized for structural engineering of high-performance chiroptical materials for spin-polarized light-emitting devices and polarization-based optoelectronics.
Batteries based on divalent metals, such as the Zn/Zn2+ pair, represent attractive alternatives to lithium-ion chemistry due to their high safety, reliability, earth-abundance, and energy density. ...However, archetypal Zn batteries are bulky, inflexible, non-rechargeable, and contain a corrosive electrolyte. Suppression of the anodic growth of Zn dendrites is essential for resolution of these problems and requires materials with nanoscale mechanics sufficient to withstand mechanical deformation from stiff Zn dendrites. Such materials must also support rapid transport Zn2+ ions necessary for high Coulombic efficiency and energy density, which makes the structural design of such materials a difficult fundamental problem. Here, we show that it is possible to engineer a solid Zn2+ electrolyte as a composite of branched aramid nanofibers (BANFs) and poly(ethylene oxide) by using the nanoscale organization of articular cartilage as a blueprint for its design. The high stiffness of the BANF network combined with the high ionic conductivity of soft poly(ethylene oxide) enable effective suppression of dendrites and fast Zn2+ transport. The cartilage-inspired composite displays the ionic conductance 10× higher than the original polymer. The batteries constructed using the nanocomposite electrolyte are rechargeable and have Coulombic efficiency of 96–100% after 50–100 charge–discharge cycles. Furthermore, the biomimetic solid-state electrolyte enables the batteries to withstand not only elastic deformation during bending but also plastic deformation. This capability make them resilient to different type of damage and enables shape modification of the assembled battery to improve the ability of the battery stack to carry a structural load. The corrugated batteries can be integrated into body elements of unmanned aerial vehicles as auxiliary charge-storage devices. This functionality was demonstrated by replacing the covers of several small drones with corrugated Zn/BANF/MnO2 cells, resulting in the extension of the total flight time. These findings open a pathway to the design and utilization of corrugated structural batteries in the future transportation industry and other fields of use.
Redox flow batteries are attractive for large-scale energy storage due to a combination of high theoretical efficiencies and decoupled power and energy storage capacities. Efforts to significantly ...increase energy densities by using nonaqueous electrolytes have been impeded by separators with low selectivities. Here, we report nanoporous separators based on aramid nanofibres, which are assembled using a scalable, low cost, spin-assisted layer-by-layer technique. The multilayer structure yields 5 ± 0.5 nm pores, enabling nanofiltration with high selectivity. Further, surface modifications using polyelectrolytes result in enhanced performance. In vanadium acetylacetonate/acetonitrile-based electrolytes, the coated separator exhibits permeabilities an order of magnitude lower and ionic conductivities five times higher than those of a commercial separator. In addition, the coated separators exhibit exceptional stability, showing minimal degradation after more than 100 h of cycling. The low permeability translates into high coulombic efficiency in flow cell charge/discharge experiments performed at cycle times relevant for large-scale applications (5 h).
A large variety of nanoparticles were synthesized during the last 25 years and are used now as “building blocks” for a variety of materials. Bottom-up solution processing of devices emerged as a ...promising direction of their technological applications because this method can (a) utilize intrinsic ability of nanocolloids to self-organize, (b) reduce high energy and equipment cost of device manufacturing, and (c) impart new functionalities to electronic devices. However the technological impact of solution processable semiconductor materialsalthough potentially considerablehas been so far limited because of the long-standing dilemma between the need for effective colloidal stabilization of nanoparticles and effective charge transport. Surfactants and other organic materials being used to synthesize and/or disperse nanocolloids introduce a barrier for charge transport between the particles. Although these barriers do make it impossible to use them in electronic devices, they certainly make it more difficult. In this review, we look into the latest progress in the solution processable devices and methods to produce electrically conductive thin films from nanoscale dispersions. We are specifically interested in the understanding of the prospects of self-assembly to facilitate charge transport and nanoscale connectivity during solution processing. The updated theoretical description of charge transport in nanoparticle solids and similar nanomaterials is also given. It includes consideration of the key mechanisms such as tunneling and cotunneling, as well as key electrical parameters characterizing transport of electrons through the surfactant-related barriers, such as coupling energy and Coulombic charging energy. Manifestations of these mechanisms in different electronic materials made from nanoparticles, nanowires, nanotubes, and nanosheets and their relative advantages and disadvantages are also discussed. We conclude the topic with a brief description of new opportunities and approaches to improve charge transport in solution processed materials from nanoscale dispersions.
Integration of nanoparticles (NPs) and other nanomaterials with existing technologies must take place in order to substantially widen the spectrum of their applications. This task can be simplified ...by taking advantage of NP assemblies provided that they retain the unique properties of nanomaterials in organized systems of larger dimensions. There is a large variety of methods of assembling NPs into superstructures containing 10-10(10) particles that include field-, bio-, and interface-directed techniques as well as self-organization. Some of them can traverse the scales from typical lengths of 10(-9) m (nano) to 10(-5) m (micro) and 10(1) m (macro) conducive to other technologies. Such dimensional transformation of nanomaterials makes possible utilization of well-established processing techniques, and hardware tools operating at these scales. Therefore, answering the question "What types of the assembly techniques are suitable for such a task?" is vital for the future application of nanoscale materials in any field of use. These techniques must result in organized structures of at least 5 × 10(-7) m in size, offer relative simplicity and fault tolerance. This review focuses on the recent development of NP assembly techniques that have the possibility of satisfying these requirements. The expected applications and future developments are also discussed.
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