Haili He

Enzymatic Plasmonic Engineering of Ag/Au Bimetallic Nanoshells and Their Use for Sensitive Optical Glucose Sensing

Enzyme works for plasmonic nanostructure: an interesting enzyme-responsive hybrid Ag/Au-GOx bimetallic nanoshell (NS) system is reported, in which control over the enzyme reaction of glucose oxidase (GOx) can automatically fine-tune the morphology (from complete NS to porous NS) and optical properties of the hybrid nanostructure. The phenomenon is further exploited as a new platform for sensitive optical glucose sensing.

Controlled synthesis of porous Ag/Au bimetallic hollow nanoshells with tunable plasmonic and catalytic properties

AbstractThis paper describes a simple and facile method for the synthesis of Ag/Au bimetallic hollow and porous nanoshells (HPNSs) with controllable porosity, using polycrystalline Ag nanoparticles as starting templates. The optical and catalytic properties of the HPNSs can be easily tuned by using hydrogen peroxide as a mild etchant to controllably dissolve Ag atoms from the precursor Ag/Au bimetallic hollow nanoshells (NSs). The surface plasmon bands of the HPNSs can be easily tuned from the visible to the near infrared (NIR) region. As a model reaction to evaluate the catalytic activity of the HPNSs, we chose the reduction of p-nitrophenol by NaBH4 to afford p-aminophenol. The porous NSs exhibit higher catalytic activity than non-porous NSs even though the latter have higher Au/Ag ratios than the former. Although the composition (Au/Ag ratio) may have some effect, the morphology (porosity) of the HPNSs plays the most important role in the catalysis. The as-synthesized plasmonic HPNSs, due to their facile aqueous-phase preparation, tunable optical properties (in the visible and NIR windows), and unique porous hollow structures, have promising potential applications in various fields ranging from biosensing, nanomedicine (drug/gene delivery, cancer theranostics, etc.), to catalysis and solar cells.

Facile and rapid synthesis of water-soluble fluorescent gold nanoclusters for sensitive and selective detection of Ag+

We report a direct one-pot approach, employing tetrakis(hydroxymethyl)phosphonium chloride (THPC) and 11-mercaptoundecanoic acid (11-MUA) as combined reducing/capping agents, for the rapid preparation of fluorescent gold nanoclusters (AuNCs) from HAuCl4 in aqueous solution at room temperature. The as-prepared AuNCs exhibit a fluorescence emission at 535 nm, a quantum yield of 1.8% and average diameters of 2.0 ± 0.5 nm. The resultant MUA/THPC–AuNCs have been exploited, for the first time, for the highly sensitive and selective detection of silver ions (Ag+) in aqueous solution when using EDTA as a masking agent for Hg2+. The fluorescence intensity quenches linearly within the range of 25 nM to 3 μM with high sensitivity (LOD = 9 nM, S/N = 3) and this sensing system has been applied for environmental water sample analysis.

Self-standing non-noble metal (Ni–Fe) oxide nanotube array anode catalysts with synergistic reactivity for high-performance water oxidation

The oxygen evolution reaction (OER) is coupled with a number of important cathodic processes, for instance water splitting for hydrogen production and other energy storage devices based on O2–H2O chemistries such as metal–air batteries and unitized regenerative fuel cells, but they are limited by the slow kinetics. Attempts to solve this problem have received wide attention recently. However, accessing and stabilizing high-oxidation-state catalytically active species to further improve the high performance for the OER has been considered a huge challenge. Here, we report a Ni–Fe oxide-based nanotube array electrode, novel in design, with strong durability and excellent and synergistically enhanced catalytic performance for the OER. The OER electrode, with a nanotube array nanostructure, shows the remarkable features of a small overpotential of 0.28 V, favourable electrode kinetics and high stability, comparing favorably with the reported performances of the best OER electrocatalysts (IrO2), which is attributed to the formation and stabilization of the favourable OER catalytically active species NiOOH that is produced and reinforced by the introduction of Fe into nanostructured materials. This feasible strategy affords a new strategy for the development of effective and robust OER electrodes.

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.

Ionic Liquid-Functionalized Fluorescent Carbon Nanodots and Their Applications in Electrocatalysis, Biosensing, and Cell Imaging

In this article, ionic liquid-functionalized carbon nanodots (IL-CDs) were produced in a simple manner by electrochemical exfoliation of graphite rods in the presence of an amino-terminated ionic liquid, and their preliminary applications were exploited. TEM and AFM results showed that these IL-CDs are about 2.6 nm in diameter. The small-sized IL-CDs have strong photoluminescence, with a quantum yield of about 11.3%, and could be used for cell imaging. Moreover, the IL-CDs exhibit good electron transfer properties and catalytic activities for O2 and H2O2 reduction. Additionally, the as-prepared IL-CDs can be applied as a matrix for immobilizing enzymes (glucose oxidase) to construct biosensors. Due to these favorable properties, IL-CDs will find promising practical applications in electrocatalysis, biosensing, and bioimaging.

Fine-tuning the LSPR response of gold nanorod–polyaniline core–shell nanoparticles with high photothermal efficiency for cancer cell ablation

Gold nanorods (GNRs) with suitable aspect ratios have strong localized surface plasmon resonance (LSPR) absorption and scattering in the 650-900 nm near-infrared region, which make them attractive for in vitro or in vivo imaging and photothermal cancer therapy. However, they often suffer from cytotoxicity and instability for practical applications, and therefore need further surface modification to solve these issues. In this study, GNRs coated with biocompatible polyaniline (PANI) were used as a stable and highly efficient photothermal agent for cancer cell ablation. Fine-tuning the LSPR response of the GNR-PANI core-shell nanoparticles via thickness-controlled coating of the PANI nanoshells, optimizes the photothermal conversion efficiency of the agent. As a result of the contributions from the GNR core and PANI shell, the capability of photothermal transduction of the resultant nanoparticles at 808 nm is greatly enhanced. After exposure to a continuous NIR laser at 808 nm for ∼5 min, cancer cells were efficiently ablated requiring only a very low laser flux of 0.6 W cm-2, the lowest value reported to date for plasmonic nanostructures, showing the great potential for photothermal cancer therapy.

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, targeting-free (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.

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 in situ 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.

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.