Ultrathin gold nanowire-functionalized carbon nanotubes for hybrid molecular sensing

Layered Architectural Fabrication of a Novel Sulfite Nanobiosensor by Encapsulation of Sulfite Oxidase on a Polypyrrole-Multiwalled Carbon Nanotubes Composite Decorated with Platinum Nanoparticles

The fabrication of a highly selective and ultrasensitive sulfite nanobiosensor based on a layered architectural fabrication aided by the encapsulation of sulfite oxidase (SOx) in Nafion (Naf) matrix on a multiwalled carbon nanotubes-polypyrrole (MWCNTs-PPy) composite decorated with platinum nanoparticles (PtNPs) is described. The MWCNTs are deposited in the inner layer on a Pt electrode during electropolymerization of pyrrole (Py), followed by decoration with a PtNPs layer and subsequent encapsulation of SOx with Naf in the third layer capped with a fourth thin PtNPs layer. Images obtained by field emission scanning electron microscopy (FESEM) reveal that high-density PtNPs are deposited onto the 3D nanostructured inner MWCNTs-PPy layer and the electrochemical behavior is investigated. A large surface area provided by the incorporation of MWCNTs in the composite and decoration with PtNPs enables increased SOx loading, SOx retention, and substantial improvement in sensing performance. The resulting layered PtNPs/SOx-Naf/PtNPs/MWCNTs-PPy nanobiosensor exhibits a fast response time (within 3 s), a linear calibration range of 20 nmm - 6 m with an excellent sensitivity of 71 µA mm-1  cm-2 and a detection limit of 5.4 nm. The nanobiosensor  was effective in discriminating against common interferants and  was successfully applied to sulfite determination in real samples.

Recent advances in nanotechnology-enhanced biosensors for α-fetoprotein detection

α-Fetoprotein (AFP) is a kind of fetal protein that is related to tumor, the increasing concentration of which gives birth to a large variety of diseases, such as liver cancer. Therefore, the detection method with super sensitivity, high selectivity, and less time consumption under trace concentrations in early stage of diseases is becoming a necessity. In recent years, nanomaterials have been regarded as significant resources for the exploration of efficient biosensors with high sensitivity, selectivity, speed, as well as simple process, due to their excellent optical, electrical, and chemical properties. In this paper, we reviewed the research progress of AFP biosensors with enhanced sensitivity and selectivity by nanoparticles. Representative examples have also been displayed in this paper to expound the nanotechnologies utilized in the early detection of AFP. Furthermore, challenges of the clinical application of AFP biosensors based on nanotechnology have been elaborated, as well as the development opportunity in this field in the future. This review provides a comprehensive overview on the various nano-biosensor for AFP detection based on functional nanotechnology.

Fabrication of High Aspect Ratio Gold Nanowires within the Microtubule Lumen

Gold nanowires have great potential use as interconnects in electronic, photonic, and optoelectronic devices. To date, there are various fabrication strategies for gold nanowires, each one associated with particular drawbacks as they utilize high temperatures, toxic chemicals, or expensive compounds to produce nanowires of suboptimal quality. Inspired by nanowire fabrication strategies that used higher-order biopolymer structures as molds for electroless deposition of gold, we here report a strategy for the growth of gold nanowires from seed nanoparticles within the lumen of microtubules. Luminal targeting of seed particles occurs through covalently linked Fab fragments of an antibody recognizing the acetylated lysine 40 on the luminal side of α-tubulin. Gold nanowires grown by electroless deposition within the microtubule lumen exhibit a homogeneous morphology and high aspect ratios with a mean diameter of 20 nm. Our approach is fast, simple, and inexpensive and does not require toxic chemicals or other harsh conditions.

Synthesis of substrate-bound seaweed-like Au nanowires with amino silane coupling agents

A seedless method has been developed to synthesize seaweed-like Au nanowires on a Au substrate. The amino silane coupling agent 3-aminopropyltriethoxysilane was employed to form the active surfaces that facilitate the one dimensional growth. The growth mechanism and controlling parameters were investigated. Furthermore, the compatibility of this synthesis with a colloidal Au substrate was also demonstrated.

Gold Nanorods: The Most Versatile Plasmonic Nanoparticles

Gold nanorods (NRs), pseudo-one-dimensional rod-shaped nanoparticles (NPs), have become one of the burgeoning materials in the recent years due to their anisotropic shape and adjustable plasmonic properties. With the continuous improvement in synthetic methods, a variety of materials have been attached around Au NRs to achieve unexpected or improved plasmonic properties and explore state-of-the-art technologies. In this review, we comprehensively summarize the latest progress on Au NRs, the most versatile anisotropic plasmonic NPs. We present a representative overview of the advances in the synthetic strategies and outline an extensive catalogue of Au-NR-based heterostructures with tailored architectures and special functionalities. The bottom-up assembly of Au NRs into preprogrammed metastructures is then discussed, as well as the design principles. We also provide a systematic elucidation of the different plasmonic properties associated with the Au-NR-based structures, followed by a discussion of the promising applications of Au NRs in various fields. We finally discuss the future research directions and challenges of Au NRs.

Gold nanoparticles to enhance ophthalmic imaging

The use of gold nanoparticles as diagnostic tools is burgeoning, especially in the cancer community with a focus on theranostic applications to both cancer diagnosis and treatment. Gold nanoparticles have also demonstrated great potential for use in diagnostic and therapeutic approaches in ophthalmology. Although many ophthalmic imaging modalities are available, there is still a considerable unmet need, in particular for ophthalmic molecular imaging for the early detection of eye disease before morphological changes are more grossly visible. An understanding of how gold nanoparticles are leveraged in other fields could inform new ways they could be utilized in ophthalmology. In this paper, we review current ophthalmic imaging techniques and then identify optical coherence tomography (OCT) and photoacoustic imaging (PAI) as the most promising technologies amenable to the use of gold nanoparticles for molecular imaging. Within this context, the development of gold nanoparticles as OCT and PAI contrast agents are reviewed, with the most recent developments described in detail.

A molecular dynamics study on the buckling behavior of single-walled carbon nanotubes filled with gold nanowires

Molecular dynamics (MD) simulations are carried out to study the buckling of pure gold nanowires (GNWs) and hybrid GNWs@single-walled carbon nanotubes (SWCNTs). The effects of geometrical parameters and endohedral filling of SWCNTs on the critical buckling force are taken into consideration. Two different types of GNWs, namely multi-shell and pentagonal GNWs, with various structures are considered. The results illustrate that the buckling force of the pure GNWs is less than those of the pure SWCNTs and hybrid structures. Also, GNWs possess higher buckling forces by increasing their cross-section area. It is observed that enclosing the GNWs by SWCNTs improves the mechanical behaviors of both CNTs and GNWs. In hybrid multi-shell GNWs@SWCNTs, by increasing the radius, the effect of encapsulation on the buckling force is more remarkable. It can be seen that the encapsulation of pentagonal GNWs has a slightly more effect on the buckling behavior than the encapsulation of multi-shell GNWs. Moreover, it is found out that by increasing the length, the buckling force decreases.

Morris M, G. Lyons M, Gun’ko YK. One Dimensional AuAg Nanostructures as Anodic Catalysts in the Ethylene Glycol Oxidation

Direct alcohol fuel cells are highly promising as efficient power sources for various mobile and portable applications. However, for the further advancement of fuel cell technology it is necessary to develop new, cost-effective Pt-free electrocatalysts that could provide efficient alcohol oxidation and also resist cross-over poisoning. Here, we report new electrocatalytic materials for ethylene glycol oxidation, which are based on AuAg linear nanostructures. We demonstrate a low temperature tunable synthesis that enables the preparation of one dimensional (1D) AuAg nanostructures ranging from nanowires to a new nano-necklace-like structure. Using a two-step method, we showed that, by aging the initial reaction mixture at various temperatures, we produced ultrathin AuAg nanowires with a diameter of 9.2 ± 2 and 3.8 ± 1.6 nm, respectively. These nanowires exhibited a high catalytic performance for the electro-oxidation of ethylene glycol with remarkable poisoning resistance. These results highlight the benefit of 1D metal alloy-based nanocatalysts for fuel cell applications and are expected to make an important contribution to the further development of fuel cell technology.

Seeded growth of gold–silver ultrathin wire–dot hybrid nanostructures

Gold–silver hybrid nanostructures in the form of “ultrathin wire–dots” are prepared in high purity via seeded growth.

Ultrasonication-assisted synthesis of high aspect ratio gold nanowires on a graphene template and investigation of their growth mechanism

We report a facile synthesis of Au nanowires (AuNWs) with a high aspect ratio (l/D) of up to 5000 on a plasma activated graphene template with ultrasound assistance. We demonstrate that the ultrasonication induced symmetry breaking of Au clusters facilitates the growth of AuNWs from the embryonic stages. Furthermore, the growth mechanism of AuNWs is systematically investigated using high resolution electron transmission microscopy (HRTEM), which reveals the unique role of the defective graphene template in directing the growth of AuNWs.

Cucurbit[n]uril (n = 6, 7) Based Carbon-Gold Hybrids with Peroxidase-Like Activity

Despite the combination of molecular recognition and local electric field enhancement endowing cucurbit[n]uril-capped metallic nanoparticles, indicating great potential in a variety of areas, prior work has paid little attention to carbonizing cucurbit[n]uril on the surface of gold nanoparticles, which may propose new carbon-gold hybrid materials with interesting applications. In this work, we developed a simple and cost-effective method to prepare carbon-gold hybrids by carbonizing cucurbit[n]uril modified gold nanoparticles. The as-prepared cucurbit[n]uril based carbon and carbon-gold hybrid materials have shown to possess peroxidase-like activity. All cucurbit[n]uril based nanomaterials exhibited high catalytic activity over a pH range 2–6 and more tolerant to high temperature (up to 60 °C) when compared to natural horseradish peroxidase.

Surface-Stress-Induced Phase Transformation of Ultrathin FeCo Nanowires

Ultrathin metal nanowires have attracted wide attention becau se oftheir unique anisotropy and surface-to-volume effects. In this study, we use ultrathin Au nanowires as the templating core to epitaxially grow magnetic iron-cobalt (FeCo) shell through metal-redox with the control on their thickness and stoichiometry. Large surface-stress-induced phase transformation in Au nanowires triggers and stabilizes metastable tetragonal FeCo nanostructure to enhance its magnetic anisotropy and coercivity. Meanwhile, under illumination, plasmon-induced hotspot in ultrathin Au nanowires enables the light-control on magnetic characteristics of FeCo shell. This study demonstrates the feasibility of surface-stress-induced phase transformation to stabilize and control metastable nanostructures for enhanced magnetic anisotropy, which is one of the key properties of functional magnetic materials.

Unconventional seed-mediated growth of ultrathin Au nanowires in aqueous solution

Ultrathin Au nanowires have garnered increasing attention in recent years because of their potential use in a range of applications due to their unique optical properties, conductivity, chemical activity, and discrete plasticity. Herein, we report an unconventional seed-mediated growth of ultrathin Au nanowires induced by hydrophobic molecules. Quite intriguingly, by adding a trace amount of hydrophobic molecules (i.e., toluene or chloroform) to the Au growth solution conventionally used for the growth of Au nanorods with cylindrical CTAB micelles as templates, CTAB-capped ultrathin Au nanowires (i.e., water-soluble ultrathin Au nanowires) were crafted. Similarly to the growth of Au nanorods, silver ions and Au seeds were crucially required to yield the water-soluble ultrathin Au nanowires. The growth mechanism of these ultrathin nanowires was also explored.

Wire-in-Tube IrOx Architectures: Alternative Label-Free Immunosensor for Amperometric Immunoassay toward α-Fetoprotein

A sensitive, label-free immunosensor based on iridium oxide (IrOx, 0≤x≤2) nanofibers, which were synthesized through a simple one-spinneret electrospinning method, was first developed for immunoassay of the cancer biomarker α-fetoprotein (AFP). The specific wire-in-tube nanostructure could be obtained and the composition of IrOx nanofibers also could be controlled through changing the annealing temperature. The unique structure and properties of IrOx nanofibers obtained at 500 °C not only led to increased electrode surface area and accelerated electron transfer kinetics but also could provide a highly stable matrix for the convenient conjugation of biomolecules together with chitosan (CS). The good electrochemical properties of the IrOx-nanofiber-modified immunosensor allowed one to detect AFP over a wide concentration range from 0.05 to 150 ng/mL, with a detection limit of 20 pg/mL. The proposed immunosensor also has been used to determine AFP in human serum with satisfactory results. The present protocol was shown to be quite promising for clinical screening of cancer biomarkers and point-of-care diagnostics applications.

The spontaneous formation and plasmonic properties of ultrathin gold-silver nanorods and nanowires stabilized in oleic acid

Ultrathin Au-Ag alloy nanorods and nanowires of different lengths and ca. 1.9 nm diameter are prepared through a low-temperature decomposition of the precursor [Au2Ag2(C6F5)4(OEt2)2]n in oleic acid. This nanostructure formation has been studied through TEM, HRTEM, EDS, HS-SPME-GC-MS and (19)F NMR spectroscopy. The UNRs and UNWs display a length-dependent broad band in the mid-IR region that is related to the longitudinal mode of the surface plasmon resonance of the ultrathin nanostructures.

Directed Assembly of Ultrathin Gold Nanowires over Large Area by Dielectrophoresis

Ultrathin Au nanowires (∼2 nm diameter) are interesting from a fundamental point of view to study structure and electronic transport and also hold promise in the field of nanoelectronics, particularly for sensing applications. Device fabrication by direct growth on various substrates has been useful in demonstrating some of the potential applications. However, the realization of practical devices requires device fabrication strategies that are fast, inexpensive, and efficient. Herein, we demonstrate directed assembly of ultrathin Au nanowires over large areas across electrodes using ac dielectrophoresis with a mechanistic understanding of the process. On the basis of the voltage and frequency, the wires either align in between or across the contact pads. We exploit this assembly to produce an array of contacting wires for statistical estimation of electrical transport with important implications for future nanoelectronic/sensor applications.

Surface Modification of Multiwalled Carbon Nanotubes with Cationic Conjugated Polyelectrolytes: Fundamental Interactions and Intercalation into Conductive Poly(methyl methacrylate) Composites

This research investigates the modification and dispersion and of pristine multiwalled carbon nanotubes (MWCNTs) through a simple solution mixing technique based on noncovalent interactions between poly(phenylene ethynylene)-based conjugated polyelectrolytes functionalized with cationic imidazolium solubilizing groups (PIM-2 and PIM-4) and MWCNTs. Spectroscopic studies demonstrated the ability of PIMs to strongly interact with and efficiently disperse MWCNTs in different solvents, mainly due to π interactions between the PIMs and the MWCNTs. Transmission electron microscopy and atomic force microscopy revealed the coating of the polyelectrolytes on the walls of the nanotubes. Scanning electron microscopy (SEM) studies confirm the homogeneous dispersion of PIM-modified MWCNTs in the poly(methyl methacrylate) (PMMA) matrix. The addition of 1 wt % PIM-modified MWCNTs to the matrix has led to a significant decrease in DC resistivity of the composite (13 orders of magnitude). The increase in electrical conductivity and the improvement in the thermal and mechanical properties of the membranes containing the PIM-modified MWCNTs is ascribed to the formation of MWCNT networks and cross-linking sites that provided channels for the electrons to move in throughout the matrix and reinforced the interface between MWCNTs and PMMA.

Synthesis of Upconversion β-NaYF₄:Nd3+/Yb3+/Er3+ Particles with Enhanced Luminescent Intensity through Control of Morphology and Phase

Hexagonal NaYF₄:Nd³⁺/Yb³⁺/Er³⁺ microcrystals and nanocrystals with well-defined morphologies and sizes have been synthesized via a hydrothermal route. The rational control of initial reaction conditions can not only result in upconversion (UC) micro and nanocrystals with varying morphologies, but also can produce enhanced and tailored upconversion emissions from the Yb³⁺/Er³⁺ ion pairs sensitized by the Nd³⁺ ions. The increase of reaction time converts the phase of NaYF₄:Nd³⁺/Yb³⁺/Er³⁺ particles from the cubic to the hexagonal structure. The added amount of oleic acid plays a critical role in the shape evolution of the final products due to their preferential attachment to some crystal planes. The adjustment of the molar ratio of F⁻/Ln³⁺ can range the morphologies of the β-NaYF₄:Nd³⁺/Yb³⁺/Er³⁺ microcrystals from spheres to nanorods. When excited by 808 nm infrared laser, β-NaYF₄:Nd³⁺/Yb³⁺/Er³⁺ microplates exhibit a much stronger UC emission intensity than particles with other morphologies. This phase- and morphology-dependent UC emission holds promise for applications in photonic devices and biological studies.

Organic-free synthesis of ultrathin gold nanowires as effective SERS substrates

Ultrathin gold nanowires (Au NWs) were synthesized in the absence of organic reagents. The obtained organic-free ultrathin Au NWs present great potential for surface-enhanced Raman scattering (SERS) applications.

New insights into electronic and geometric effects in the enhanced photoelectrooxidation of ethanol Using ZnO nanorod/ultrathin Au nanowire hybrids

Oxidation of small organic molecules in a fuel cell is a viable method for energy production. However, the key issue is the development of suitable catalysts that exhibit high efficiencies and remain stable during operation. Here, we demonstrate that amine-modified ZnO nanorods on which ultrathin Au nanowires are grown act as an excellent catalyst for the oxidation of ethanol. We show that the modification of the ZnO nanorods with oleylamine not only modifies the electronic structure favorably but also serves to anchor the Au nanowires on the nanorods. The adsorption of OH(-) species on the Au nanowires that is essential for ethanol oxidation is facilitated at much lower potentials as compared to bare Au nanowires leading to high activity. While ZnO shows negligible electrocatalytic activity under normal conditions, there is significant enhancement in the activity under light irradiation. We demonstrate a synergistic enhancement in the photoelectrocatalytic activity of the ZnO/Au nanowire hybrid and provide mechanistic explanation for this enhancement based on both electronic as well as geometric effects. The principles developed are applicable for tuning the properties of other metal/semiconductor hybrids with potentially interesting applications beyond the fuel cell application demonstrated here.

Surface plasmon resonance in gold ultrathin nanorods and nanowires

We synthesized and measured optical extinction spectra of Au ultrathin (diameter: ∼1.6 nm) nanowires (UNWs) and nanorods (UNRs) with controlled lengths in the range 20-400 nm. The Au UNWs and UNRs exhibited a broad band in the IR region whose peak position was red-shifted with the length. Polarized extinction spectroscopy for the aligned Au UNWs indicated that the IR band is assigned to the longitudinal mode of the surface plasmon resonance.