Nanoprisms Research Articles

Self-template synthesis of lychee like Mn-doped Co2P yolk-shell spheres for enhanced hydrogen evolution reaction activity

Designing an electrocatalyst for hydrogen production from water splitting that is highly efficient, stable, and free of noble metals is necessary but challenging. The phosphorus compound is considered a viable candidate for producing hydrogen from water split, but its electrocatalytic performance needs further improvement. Herein, we present an easy and straightforward method for constructing Mn-doped Co2P yolk-shell lychee spheres. The Co nano prisms are used as a self-sacrificing template to conduct an ion exchange reaction with manganese ions, constructing Co oxide yolk-shell spheres with Mn–Co hydroxide nano-blocks. After in-suit phosphating at low temperature, Mn-doped Co2P with yolk-shell structure and lychee morphology is formed. The Mn-doped Co2P with an optimized Mn and Co molar ratio (0.125) exhibits excellent hydrogen evolution performance in alkaline and acidic electrolyte. The overpotentials can reach 10 mA cm−2 at 98 mV and 72 mV, respectively, and the Mn–Co2P-0.125 catalyst has faster electron transfer efficiency and larger electrochemically active surface area. The experimental results ascertain that doping an appropriate amount of Mn significantly changes the morphology and structure, thereby affecting the exposure of active sites, and modulating the electronic structure around Co2P. Under the dual regulation of morphology and electronic structure, the electrocatalytic process is accelerated, enhancing its catalytic activity.

Colorimetric and naked-eye detection of arsenic(iii) using a paper-based microfluidic device decorated with silver nanoparticles.

Arsenic (As) as a metal ion has long-term toxicity and its presence in water poses a serious threat to the environment and human health. So, rapid and accurate recognition of traces of As is of particular importance in environmental and natural resources. In this study, a fast and sensitive colorimetric method was developed using silver nano prisms (Ag NPrs), cysteine-capped Ag NPrs, and methionine-capped Ag NPrs for accurate detection of arsenic-based on transforming the morphology of silver nanoparticles (AgNPs). The generated Ag atoms from the redox reaction of silver nitrate and As(iii) were deposited on the surface of Ag NPrs and their morphology changed to a circle. The morphological changes resulted in a change in the color of the nanoparticles from blue to purple, which was detectable by the naked eye. The rate of change was proportional to the concentration of arsenic. The changes were also confirmed using UV-Vis absorption spectra and showed a linear relationship between the change in adsorption peak and the concentration of arsenic in the range of 0.0005 to 1 ppm with a lower limit of quantification (LLOQ) of 0.0005 ppm. The proposed probes were successfully used to determine the amount of As(iii) in human urine samples. In addition, modified microfluidic substrates were fabricated with Ag NPrs, Cys-capped Ag NPrs, and methionine-capped Ag NPrs nanoparticles that are capable of arsenic detection in the long-time and can be used in the development of on-site As(iii) detection kits. In addition, silver nanowires (AgNWs) were used as a probe to detect arsenic, but good results were not obtained in human urine specimens and paper microfluidic platforms. In this study, for the first time, AgNPs were developed for optical colorimetric detection of arsenic using paper-based microfluidics. Ag NPrs performed best in both optical and colorimetric techniques. Therefore, they can be a promising option for the development of sensitive, inexpensive, and portable tools in the environmental and biomedical diagnosis of As(iii).

Direct As(V) Determination Using Screen-Printed Electrodes Modified with Silver Manoparticles.

Carbon-nanofiber-based screen-printed electrodes modified with silver nanoparticles (Ag-NP-SPCNFEs) were tested in a pioneering manner for the direct determination of As(V) at low μg L−1 levels by means of differential pulse anodic stripping voltammetry. Screen-printed electrodes were modified with two different types of Ag-NPs, nanoseeds (NS), and nanoprisms (NPr) and characterized both microscopically and electrochemically. Furthermore, after optimizing the direct voltammetric determination of As(V), the analytical performance of considered sensors was compared for the direct determination of As(V). These results suggest that Ag-NS offer a better analytical response compared to Ag-NPr, with a detection and quantification limit of 0.6 and 1.9 µg L−1, respectively. The proposed methodology was validated using a spiked tap water sample with a very high reproducibility and good agreement with inductively coupled plasma-mass spectrometry (ICP-MS) measurements.

In vivo comparison of the biodistribution and long-term fate of colloids - gold nanoprisms and nanorods - with minimum surface modification.

Aim: To study the difference in biodistribution of gold nanoprisms (NPr) and nanorods (NR), PEGylated to ensure colloidal stability. Materials & methods: Surface changes were studied for nanoparticles in different media, while the biodistribution was quantified and imaged in vivo. Results: Upon interaction with the mouse serum, NR showed more abrupt changes in surface properties than NPr. In the in vivo tests, while NPr accumulated similarly in the spleen and liver, NR showed much higher gold presence in the spleen than in liver; together with some accumulation in kidneys, which was nonexistent in NPr. NPr were cleared from the tissues 2months after administration, while NR were more persistent. Conclusion: The results suggest that the differential biodistribution is caused by size-/shape-dependent interactions with the serum.

Improvement of ultrafast holographic performance in silver nanoprisms dispersed photopolymer.

This work demonstrates the grating formation of bulk nanoparticle polymer composites through an improved interference optical system under ultrafast nanoseconds exposure of a silver nanoprisms (NPs) dispersed photo-polymerizable mixture in the case of 532 nm wavelength. The polymerizable mixture is composed of phenathrenequinone (PQ) (photoinitiator) and methyl methacrylate (MMA) (monomer). The mechanism in this bulk nanoparticle polymer composite is analyzed by mixing nonlocal polymerization driven diffusion (NPDD) model and absorption modulation caused by the spatial concentration distribution difference of silver NPs. We find that the attenuation of diffraction efficiency under pulsed exposure is due to the reciprocity law failure. This work presents an analysis of the cause of reciprocity failure and improvement in holographic properties by doping silver NPs. The optimized photopolymer presents diffraction efficiencies as high as 51.4% with 1.8 μs cumulative pulsed exposure. Cumulative gratings strength is also enhanced by 70% while doping silver NPs under 1.5 μs cumulative pulsed exposure.

Synthesis of Triangular Silver and Gold Nanoprisms Using Consensus Sequence Tetratricopeptide Repeat Proteins.

Anisotropic metallic nanoparticles, such as Au and Ag nanoprisms (NPSMs), have received tremendous attention for their application in catalysis, molecular sensing, signal amplification, bioimaging, and therapeutic applications due to their shape-dependent optical and physical properties. Herein, we present a protein-enabled synthetic strategy for the seeded growth of silver and gold NPSMs with low shape polydispersity, narrow size distribution, and tailored plasmonic absorbance. During the initial seed nucleation step, consensus sequence tetratricopeptide repeat (CTPR) proteins are utilized as potent stabilizers to facilitate the formation of planar-twinned Ag seeds. High yield production of well-defined Ag/Au NPSMs is achieved, respectively, by adding CTPR-stabilized Ag seeds into the growth solutions containing metal precursor, mild reducing agent, sodium halide, and additional CTPR.

Silver nanoprisms self-assembly on differently functionalized silica surface

In this work colloidal silica/silver nanoprisms (NPRs) composite coatings were made. Firstly colloidal silica sols were synthesized by sol-gel method and produced coatings on glass by dip-coating technique. Next coatings were silanized by (3-Aminopropyl)triethoxysilane (APTES), N-[3-(Trimethoxysilyl)propyl]ethylenediamine (AEAPTMS), (3- Mercaptopropyl)trimethoxysilane (MPTMS). Silver NPRs where synthesized via seed-mediated method and high yield of 94±15 nm average edge length silver NPRs were obtained with surface plasmon resonance peak at 921 nm. Silica-Silver NPRs composite coatings obtained by selfassembly on silica coated-functionalized surface. In order to find the most appropriate silanization way for Silver NPRs self-assembly, the composite coatings were characterized by scanning electron microscopy (SEM), dynamic light scattering (DLS), water contact angle (CA) and surface free energy (SFE) methods. Results have showed that surface functionalization is necessary to achieve self-assembled Ag NPRs layer. MPTMS silanized coatings resulted sparse distribution of Ag NPRs. Most homogeneous, even distribution composite coatings obtained on APTES functionalized silica coatings, while AEAPTMS induced strong aggregation of Silver NPRs.

Dissecting the molecular mechanism of apoptosis during photothermal therapy using gold nanoprisms.

The photothermal response of plasmonic nanomaterials can be exploited for a number of biomedical applications in diagnostics (biosensing and optoacoustic imaging) and therapy (drug delivery and photothermal therapy). The most common cellular response to photothermal cancer treatment (ablation of solid tumors) using plasmonic nanomaterials is necrosis, a process that releases intracellular constituents into the extracellular milieu producing detrimental inflammatory responses. Here we report the use of laser-induced photothermal therapy employing gold nanoprisms (NPRs) to specifically induce apoptosis in mouse embryonic fibroblast cells transformed with the SV40 virus. Laser-irradiated "hot" NPRs activate the intrinsic/mitochondrial pathway of apoptosis (programmed cell death), which is mediated by the nuclear-encoded proteins Bak and Bax through the activation of the BH3-only protein Bid. We confirm that an apoptosis mechanism is responsible by showing how the NPR-mediated cell death is dependent on the presence of caspase-9 and caspase-3 proteins. The ability to selectively induce apoptotic cell death and to understand the subsequent mechanisms provides the foundations to predict and optimize NP-based photothermal therapy to treat cancer patients suffering from chemo- and radioresistance.

Synthesis of thermally stable Ag@TiO2 core–shell nanoprisms and plasmon–enhanced optical properties for a P3HT thin film

We develop a facile method to synthesize Ag@TiO2 core–shell nanoprisms (NPs) with a tunable shell thickness through a simple sol–gel route. The thickness of the TiO2 shell can be precisely tuned from 1 to 15 nm via changing the reaction time and amount of TiO2 sol–gel precursor. The localized surface plasmon resonance (LSPR) absorption band shows a red-shift of over a hundred nanometers with the increasing TiO2 shell thickness. The thermal stability of the Ag NPs is significantly improved due to the introduction of the TiO2 shell. We investigate the enhanced absorption and fluorescence of poly(3-hexylthiophene) (P3HT) via coating bare Ag and Ag@TiO2 core–shell NPs with P3HT. A similar absorption enhancement indicates that the LSPR absorption enhancement is not affected by the ultra-thin TiO2 shell. Weak and significant fluorescence enhancements are observed for the P3HT hybrid film with bare Ag NPs and Ag@TiO2 core–shell NPs, respectively. The bare Ag NPs work as both an enhancement element and a recombination center, which quench the P3HT fluorescence to some degree. The recombination of the charge carriers is effectively depressed by introducing the ultra-thin TiO2 shell, which blocks the hole transfer to the Ag NPs.

Effect of shape and interstice on surface enhanced Raman scattering (SERS) of molecules adsorbed on gold nanoparticles in the near‐dipole and quadrupole regions

Surface enhanced Raman scattering (SERS) of adsorbed molecule on colloidal gold nanoparticles of different shapes, namely nanospheres (NSs), nanorods (NRs), and nanoprisms (NPs) as well as the three NPs arrays of different interstice prepared by NS lithography, are studied with incident wavenumbers in the near‐dipole and near‐quadrpole regions of the nanoparticles. In the colloidal gold nanoparticles, the SERS enhancement is the largest for the sharp tip followed by the truncated tip NPs, then the NRs and least enhancement for the NSs. This decreasing order of enhancement occurs although the incident wavenumber was near the dipole resonance of NSs and the quadrupole resonance for the NPs. These varied enhancements are explained in part as due to the binding energies of the nanocrystal facets, but the larger contribution results from the plasmon electromagnetic fields. A parallel finite difference time domain (FDTD) calculations were carried out, which corporate the experimental results and show agreement with ratios of the SERS enhancement for the different shapes. The normalized SERS intensity for NPs of different interstice distances show a sharp rise with the decrease of the interstice distances because of interparticle dipolar and quadrupolar coupling as evidenced also by FDTD calculations. Furthermore, these calculations show that the enhancement is polarization independent for an incident wavelength near quadrupole resonance but polarization dependent for an incident wavelength near the plasmon dipole transition. In the last case, the enhancement is larger by an order of magnitude for a polarization parallel to the NPs bisector than for polarization normal to the bisector with no hot spots for the relatively large interstice dimensions used. Copyright © 2012 John Wiley & Sons, Ltd.

Tailoring the Synthesis and Heating Ability of Gold Nanoprisms for Bioapplications

The paper describes a novel and straightforward wet-chemical synthetic route to produce biocompatible single-crystalline gold tabular nanoparticles, herein called nanoprisms (NPRs) due to their characteristic shape. Besides the novelty of the method to produce NPRs with an unprecedented high yield, the synthesis avoids the use of highly toxic cetyltrimethylammonium bromide (CTAB), the most widely used surfactant for the synthesis of gold anisotropic nanoparticles such as nanorods or nanoprisms. The method presented here allows for tuning the edge length of NPRs in the range of 100-170 nm by adjusting the final concentration/molar ratio of gold salt and reducing agent (thiosulfate), while the thickness of NPRs remained constant (9 nm). Thus, the surface plasmon band of NPRs can be set along the near-infrared (NIR) range. The resulting NPRs were derivatized with heterobifunctional polyethylene glycol (PEG) and 4-aminophenyl β-D-glucopyranoside (glucose) chains to improve their stability and cellular uptake, respectively. The heating properties of colloidal solutions of NPRs upon 1064 nm light illumination were evaluated. As a proof of concept, the biocompatibility and suitability of functional NPRs as photothermal agents were studied in cell cultures. Due to their biocompatibility (avoiding CTAB), ease of production, ease of functionalization, and remarkable heating features, the NPRs discussed herein represent a significant advance in the biocompatibility of nanoparticles and serve as an attractive alternative to those currently in use as plasmonic photothermal agents.

Synthesis of Silver Nanoprisms with Variable Size and Investigation of Their Optical Properties: A First-Year Undergraduate Experiment Exploring Plasmonic Nanoparticles

A robust and reasonably simple experiment is described that introduces students to the visualization of nanoscale properties and is intended for a first-year laboratory. Silver nanoprisms (NPs) that display different colors due to variation of their plasmonic absorption with respect to size are prepared. Control over the size of the silver nanoprisms is achieved using a novel approach, where bromide is added to the reaction as a size-determining agent, and silver ions are reduced by borohydride in the presence of citrate and peroxide as stabilizing and shape-directing agents, respectively. In a typical experiment, four dispersions of silver nanoprisms with different sizes are produced that are colored from blue (largest) to yellow (smallest). The colors attainable in between are violet, purple, red, and orange. The synthesis of these colored silver NPs is described for the first time as an undergraduate experiment. Once synthesized, the nanoprisms are characterized using UV−vis spectroscopy, and a Beer’s ...

Electric Field Enhancement of Nano Gap of Silver Prisms

Using numerical calculation, we examine the effects of gap distance ofa pair of nano gap silver prisms with rounded corners on the locallight intensity enhancement. Two peaks due to localized surface plasmon(LSP) excitation are observed in a wavelength range from 900 nm to300 nm. The results demonstrate that peaks at a longer and a shorterwavelength corresponded to dipole-like and quadrupole-like LSPresonances, respectively. It is found that a gap distance up to 20 nmprovides larger light intensity enhancement than that of a singlesilver nano prism with rounded corners. Furthermore, nano gap silverprisms are fabricated by direct focused ion beam processing, and wemeasure the scattering light spectrum of a pair of nano prisms by aconfocal optical system. However, the two LSP peaks are not observed invisible range because the sizes of the nano gap and prisms are toolarge.