Facile One-Step Photochemical Fabrication and Characterization of an Ultrathin Gold-Decorated Single Glass Nanopipette

The inner surface of a conical glass nanopipette was modified with ultrathin gold film by a facile one-step photochemical approach, using HAuCl₄ and ethanol as common reagents with the aid of UV irradiation. The method is simple, straightforward, time-saving, and environmentally friendly. The morphology and component of the as-prepared ultrathin gold film was thoroughly characterized by transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) analysis, and X-ray photoelectron spectroscopy (XPS). The mechanism of the gold film growth was briefly discussed. Other small photochemical reagents with a hydroxy group, e.g., ethylene glycol, methanol, and glucose, may also work but with a different rate of reaction. The facile ultrathin gold decoration of a single glass nanopipette renders the glass nanopipette-based nanopore platform very easy for surface chemical modifications and potential sensing applications. The success of the gold decoration on the inner surface of the glass nanopore was further confirmed electrochemically by surface modification of a small thiol molecule (cysteine), and the pH (surface charge)-dependent ionic current rectification behaviors through the nanopore were investigated. Due to its facile preparation, the method and the Au-decorated glass nanopore would find promising and extended applications in ultrasensitive detection and biosensing

Wet-Chemical Enzymatic Preparation and Characterization of Ultrathin Gold-Decorated Single Glass Nanopore

The conical glass nanopore was modified through layer-by-layer electrostatic deposition of a monolayer of glucose oxidase, and then an ultrathin gold film was formed <i>in situ</i> through enzyme-catalyzed reactions. The morphology and components of single glass nanopore before and after ultrathin Au deposition were characterized by transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) analysis, respectively. In particular, the quenching of the quantum dots fluorescence in the nanopore tip zone further illustrated that the gold nanofilm was successfully deposited on the inner wall of the single glass nanopore. The Au thin films make the glass nanopores more biologically friendly and allow the nanopores facile functionalization of the surface through the Au–S bonds. For instance, the ionic current rectification (ICR) properties of the gold-decorated glass nanopores could be switched readily at different pHs by introducing different thiol molecules

High-Efficiency Plasmon-Enhanced and Graphene-Supported Semiconductor/Metal Core–Satellite Hetero-Nanocrystal Photocatalysts for Visible-Light Dye Photodegradation and H₂ Production from Water

Solar-driven photocatalytic process based on electron–hole pair production in semiconductors is a long sought-after solution to a green and renewable energy and has attracted a renaissance of interest recently. The relatively low photocatalytic efficiency, however, is a main obstacle to their practical applications. A promising attempt to solve this problem is by combined use of metal nanoparticles, by taking advantage of strong and localized plasmonic near-field to enhance solar absorption and to increase the electron–hole pair generation rate at the surface of semiconductor. Here, we report a semiconductor/metal visible-light photocatalyst based on CdSe/CdS-Au (QD-Au) core–satellite heteronanocrystals, and assemble them on graphene nanosheets for better photocatalytic reaction. The as-synthesized photocatalyst exhibits excellent plasmon-enhanced photocatalytic activities toward both photodegradation of organic dye and visible-light H₂ generation from water. The H₂ evolution rate achieves a maximum of 3113 μmol h^–1 g^–1 for the heteronanocrystal-graphene composites, which is about 155% enhancement compared to nonplasmonic QD-G sample and 340% enhancement compared to control QD-Au-G sample, and the apparent quantum efficiency (QE) reaches to 25.4% at wavelength of 450 nm

Significantly Enhancing Supercapacitive Performance of Nitrogen-doped Graphene Nanosheet Electrodes by Phosphoric Acid Activation

In this work, we present a new method to synthesize the phosphorus, nitrogen contained graphene nanosheets, which uses dicyandiamide to prevent the aggregation of graphene oxide and act as the nitrogen precursor, and phosphoric acid (H₃PO₄) as the activation reagent. We have found that through the H₃PO₄ activation, the samples exhibit the remarkably enhanced supercapacitive performance, and depending on the amount of H₃PO₄ introduced, the specific capacitance of the samples is gradually increased from 7.6 to 244.6 F g^–1. Meanwhile, the samples also exhibit the good rate capability and excellent stability (up to 10 000 cycles). Through the transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Brunauer–Emmett–Teller analyses, H₃PO₄ treatment induced large pore volume and phosphorus related function groups in the product are assumed to response for the enhancement

Controllable Shrinking of Glass Capillary Nanopores Down to sub-10 nm by Wet-Chemical Silanization for Signal-Enhanced DNA Translocation

Diameter is a major concern for nanopore based sensing. However, directly pulling glass capillary nanopore with diameter down to sub-10 nm is very difficult. So, post treatment is sometimes necessary. Herein, we demonstrate a facile and effective wet-chemical method to shrink the diameter of glass capillary nanopore from several tens of nanometers to sub-10 nm by disodium silicate hydrolysis. Its benefits for DNA translocation are investigated. The shrinking of glass capillary nanopore not only slows down DNA translocation, but also enhances DNA translocation signal and signal-to-noise ratio significantly (102.9 for 6.4 nm glass nanopore, superior than 15 for a 3 nm silicon nitride nanopore). It also affects DNA translocation behaviors, making the approach and glass capillary nanopore platform promising for DNA translocation studies

Smart Plasmonic Glucose Nanosensors as Generic Theranostic Agents for Targeting-Free Cancer Cell Screening and Killing

Fast and accurate identification of cancer cells from healthy normal cells in a simple, generic way is very crucial for early cancer detection and treatment. Although functional nanoparticles, like fluorescent quantum dots and plasmonic Au nanoparticles (NPs), have been successfully applied for cancer cell imaging and photothermal therapy, they suffer from the main drawback of needing time-consuming targeting preparation for specific cancer cell detection and selective ablation. The lack of a generic and effective method therefore limits their potential high-throughput cancer cell preliminary screening and theranostic applications. We report herein a generic in vitro method for fast, <i>targeting-free</i> (avoiding time-consuming preparations of targeting moiety for specific cancer cells) visual screening and selective killing of cancer cells from normal cells, by using glucose-responsive/-sensitive glucose oxidase-modified Ag/Au nanoshells (Ag/Au-GOx NSs) as a smart plasmonic theranostic agent. The method is generic to some extent since it is based on the distinct localized surface plasmon resonance (LSPR) responses (and colors) of the smart nanoprobe with cancer cells (typically have a higher glucose uptake level) and normal cells

Free-Standing Monolayered Metallic Nanoparticle Networks as Building Blocks for Plasmonic Nanoelectronic Junctions

The effective coupling of optical surface plasmons (SPs) and electron transport in a plasmonic-electronic device is one of the fundamental issues in nanoelectronics and the emerging field of plasmonics, and offer promise in providing a solution to next generation nanocircuits in which all coupling is in the near field. Attempts toward this end, however, are limited because of the integration challenge to compatible nanodevices. To date, direct electrical detection of SP-electron coupling from metallic nanostructures alone are not reported, and thus it remains a great experimental challenge. In this paper, we succeed in preparing a new suspended-film-type nanoelectronic junction, in which free-standing 2D fractal nanoparticle networks act as plasmonically active nanocomponents. Direct electrical detection of optical collective SPs was evidenced by photocurrent response of the junction upon illumination. Room-temperature <i>I</i>–<i>V</i> characteristics, differing from nonlinear to Ohmic behaviors, are found to be sensitive to the nanometer-scale morphology changes of the nanomembranes. The finding and approach may enable the development of advanced plasmonic nanocircuits and new nanoelectronics, nanophotonics, and (solar) energy applications

Synthesis of Monodisperse Plasmonic Au Core–Pt Shell Concave Nanocubes with Superior Catalytic and Electrocatalytic Activity

This work describes a facile and effective method for synthesis of concave Au@Pt nanocubes via a galvanic replacement process using preformed Au@Ag truncated nanocubes as templates. We found that the as-prepared concave Au@Pt nanocubes exhibit a unique plasmonic optical property and catalytic activity higher than that of a commercial Pt black catalyst in the catalytic reduction of <i>p</i>-nitrophenol into <i>p</i>-aminophenol by NaBH₄, and more importantly, the as-prepared concave Au@Pt nanocubes exhibit significantly higher electrocatalytic activity and greater durability for the ethanol oxidation reaction in alkaline media than commercial Pt black. The as-synthesized plasmonic Au core–Pt shell nanocubes, because of their well-defined concave core–shell nanostructure and high level of electrocatalytic performance, may find promising potential applications in various fields, such as ethanol fuel cells

Graphene Oxide-Supported Ag Nanoplates as LSPR Tunable and Reproducible Substrates for SERS Applications with Optimized Sensitivity

Nanoparticles and nanohybrids with well-defined structures, along with tunable localized surface plasmon resonance (LSPR) properties and optimized sensitivity, are crucial and highly desired for surface-enhanced Raman spectroscopy (SERS) applications. In this article, we report on a very promising and flexible SERS platforms with a tunable LSPR response and sensitivity based on Ag nanoplates and graphene oxide (GO). The SERS detection sensitivity can be easily optimized and significantly improved by fine-tuning the LSPR band of the Ag nanoplate/GO substrates (to enhance the SERS response) during sample preparation. We applied the as-prepared SERS platform for sensitive SERS detection of 4-mercaptobenzoic acid and 4-aminothiophenol and found that the SERS signal varied markedly (by ∼10–15-fold) with the fine-tuning of the LSPR band. The SERS enhancement factor of the Ag nanoplate/GO complexes was more than 10⁴ times larger than that obtained using spherical Ag nanoparticles. The as-prepared Ag nanoplate/GO platforms, because of their excellent stability and tunable LSPR properties, will find promising practical SERS applications

In Situ Nanoplasmonic Probing of Enzymatic Activity of Monolayer-Confined Glucose Oxidase on Colloidal Nanoparticles

In situ probing protein–particle interactions and activities of proteins on colloidal nanoparticle (NP) surfaces is a long-standing key challenge in understanding the nanobio interfaces and virtually important for a variety of biological and biomedical applications. The interactions of NPs with proteins, for instance, are known to form NP bioconjugates or protein coronas; protein surface immobilization and molecular layer-by-layer deposition techniques are widely used, but a clear understanding of the confinement effect on protein activity by molecular coating, at the monolayer level, remains poorly understood. We explore here a novel approach, using colloidal plasmonic nanocomplexes coated with glucose oxidase (GOx) as self-sensing nanoprobes for in situ optical probing of surface-confined enzymatic activity, which is at least 1–2 orders of magnitude more sensitive than standard colorimetric assays for detecting GOx activity. We found that enzymatic activity of monolayer-confined GOx on colloidal NPs was significantly enhanced as compared with free GOx (also proved by conformational changes from circular dichroism studies), with a low apparent Michaelis–Menten constant <i>K</i>_m of ∼0.115 mM and high turnover <i>k</i>_cat/<i>K</i>_m of ∼8394 M^–1·s^–1; compared with the “anchored-type” suspending GOx, the outmost polyelectrolyte monolayer-protected “sandwiched-type” GOx exhibits significantly improved enzymatic activities toward higher temperatures and wider pH range. This finding is of fundamental important and instructive for safe use of such nanomaterials for bioapplications