Shell-isolated Nanoparticle Research Articles

Shell-Isolated Nanoparticle-Enhanced Luminescence of Metallic Nanoclusters.

Metallic nanoclusters (NCs) have molecular-like structures and unique physical and chemical properties, making them an interesting new class of luminescent nanomaterials with various applications in chemical sensing, bioimaging, optoelectronics, light-emitting diodes (LEDs), etc. However, weak photoluminescence (PL) limits the practical applications of NCs. Herein, an effective and facile strategy of enhancing the PL of NCs was developed using Ag shell-isolated nanoparticle (Ag SHIN)-enhanced luminescence platforms with tuned SHINs shell thicknesses. 3D-FDTD theoretical calculations along with femtosecond transient absorption and fluorescence decay measurements were performed to elucidate the enhancement mechanisms. Maximum enhancements of up to 231-fold for the [Au7Ag8(C≡CtBu)12]+ cluster and 126-fold for DNA-templated Ag NCs (DNA-Ag NCs) were achieved. We evidenced a novel and versatile method of achieving large PL enhancements with NCs with potential for practical biosensing applications for identifying target DNA in ultrasensitive surface analysis.

Investigation of copper oxidation states in plasmonic nanomaterials by XAS and Raman spectroscopy.

Plasmonic core-shell-isolated nanoparticles are promising nanoplatforms for photocatalysis and for low detection analysis. This paper describes the characterization of a 2,2'-bipyridine phosphonate functionalized Ag@TiO2 nanocomposite which complexes copper ions by enhanced Raman spectroscopy and X-ray absorption (XANES and EXAFS). We distinguished Cu(i) from Cu(ii) complexes using shell-isolated nanoparticle enhanced Raman (SHINERS) combined with XAS spectroscopy.

Oxygen Reduction at Pt{Hkl} Electrodes in an Alkali Metal Ion Containing Aprotic Solvent

Metal-oxygen battery cathodes utilise the reversible redox species of oxygen in the presence of metal ions. However the oxygen reduction and evolution reaction mechanisms are yet to be conclusively determined. In order to elucidate the effect of surface structure on the oxygen reduction reaction (ORR) a method of preparing clean, well-defined Pt{hkl} electrodes for adsorption studies in non-aqueous solvents is described. The ORR in MClO4 (M = Li+, Na+, K+) containing dimethyl sulfoxide (DMSO) as the electrolyte highlights the structural sensitivity of the ORR under these conditions. Using cyclic voltammetry (CV) and in situ electrochemical Shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS), the various stages of oxygen reduction as a function of i) potential, ii) metal ion concentration and iii) sweep rate are investigated. In the sodium system it is found that on Pt{111} and Pt{110}-(1x1) terraces, a long lived surface sodium peroxide species is formed reversibly, whereas on Pt{100} and polycrystalline electrodes, this species is unstable and dissolves into the bulk electrolyte. On all surfaces studied, the initial reduction pathway corresponds to the formation of a surface sodium superoxide phase. In the absence of sodium ions, superoxide formation takes place exclusively followed by superoxide formation into the bulk of the electrolyte with no evidence of peroxide formation. The discovery that Pt surfaces can control the reaction pathway between superoxide and peroxide species opens up the development of practical electrocatalysts capable of controlling the desired reaction pathway towards Na2O2 to deliver Na-O2 batteries with higher theoretical specific energies.

Detection of circulating tumor cells in blood by shell-isolated nanoparticle \u2013 enhanced Raman spectroscopy (SHINERS) in microfluidic device

Isolation and detection of circulating tumor cells (CTCs) from human blood plays an important role in non- invasive screening of cancer evolution and in predictive therapeutic treatment. Here, we present the novel tool utilizing: (i) the microfluidic device with (ii) incorporated photovoltaic (PV) based SERS-active platform, and (iii) shell-isolated nanoparticles (SHINs) for simultaneous separation and label-free analysis of circulating tumour cells CTCs in the blood specimens with high specificity and sensitivity. The proposed microfluidic chip enables the efficient size – based inertial separation of circulating cancer cells from the whole blood samples. The SERS-active platform incorporated into the microfluidic device permits the label-free detection and identification of isolated cells through the insight into their molecular and biochemical structure. Additionally, the silver nanoparticles coated with an ultrathin shell of silica (Ag@SiO2) was used to improve the detection accuracy and sensitivity of analysed tumor cells via taking advantages of shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). The empirical analysis of SHINERS spectra revealed that there are some differences among studied (HeLa), renal cell carcinoma (Caki-1), and blood cells. Unique SHINERS features and differences in bands intensities between healthy and cancer cells might be associated with the variations in the quantity and quality of molecules such as lipid, protein, and DNA or their structure during the metastasis cancer formation. To demonstrate the statistical efficiency of the developed method and improve the differentiation for circulating tumors cells detection the principal component analysis (PCA) has been performed for all SHINERS data. PCA method has been applied to recognize the most significant differences in SHINERS data among the three analyzed cells: Caki-1, HeLa, and blood cells. The proposed approach challenges the current multi-steps CTCs detection methods in the terms of simplicity, sensitivity, invasiveness, destructivity, time and cost of analysis, and also prevents the defragmentation/damage of tumor cells and thus leads to improving the accuracy of analysis. The results of this research work show the potential of developed SERS based tool for the separation of tumor cells from whole blood samples in a simple and minimally invasive manner, their detection and molecular characterization using one single technology.

Functionalized core-shell Ag@TiO2 nanoparticles for enhanced Raman spectroscopy: a sensitive detection method for Cu(ii) ions.

This paper demonstrates the use of surface plasmon resonance of core-shell Ag@TiO2 particles in SHINERS experiments. A copper(ii) complex grafted onto Ag@TiO2 surface was probed by Raman spectroscopy using resonance excitation profiles vs. excitation wavelengths (514, 633 and 785 nm) to tune the Raman signals. Enhancement factors of the SHINERS assembly have been estimated and compared to the SERS effect of unmodified silver NPs colloidal dispersions. Finally, the grafting of the copper(ii) complex onto Ag@TiO2 was advantageously compared to the grafting onto Ag@SiO2 shell.

Shell-Isolated Nanoparticle-Enhanced Phosphorescence.

The emerging field of plasmonics has promoted applications of optical technology, especially in plasmon-enhanced spectroscopy (PES). However, in plasmon-enhanced fluorescence (PEF), "metal loss" could significantly quench the fluorescence during the process, which dramatically limits its applications in analysis and high-resolution imaging. In this report, silver core silica shell-isolated nanoparticles (Ag@SiO2 NPs or SHINs) with a tunable thickness of shell are used to investigate the interactions between NPs and emitters by constructing coupling and noncoupling modes. The plasmonic coupling mode between Ag@SiO2 NPs and Ag film reveals an exceeding integrating spectral intensity enhancement of 330 and about 124 times that of the radiative emission rate acceleration for shell-isolated nanoparticle enhanced phosphorescence (SHINEP). The experimental findings are supported by theoretical calculations using the finite-element method (FEM). Hence, the SHINEP may provide a novel approach for understanding the interaction of plasmon and phosphorescence, and it holds great potential in surface detection analysis and singlet-oxygen-based clinical therapy.

A REVIEW OF RAMAN, SURFACE-ENHANCED RAMAN SCATTERING (SERS) AND RELATED SPECTROSCOPIC TECHNIQUES APPLIED TO BIOMOLECULES IN BIOMATERIALS

The development of new biomaterials has gained increasing attention in the last decade. One of the most important aspects in the development of these new materials is to understand the chemical cues presents in the native niche. Among all the techniques currently available for measuring those interactions, Raman spectroscopy offers a unique and non-invasive tool for exploring the behavior of the components within a given biomaterial and their surrounding microenvironment. This technique exploits the unique molecular vibrational fingerprints for pinpointing those interactions. The vibrational response can be improved to the single molecule level, in the presence of metal nanoparticles (NPs) with plasmonic properties (silver, gold and copper) in the so-called Surface- Enhanced Raman Scattering (SERS), which can be used for in-situ measurements. Another technique recently developed is the Shell-Isolated Nanoparticle- Enhanced Raman Spectroscopy (SHINERS), which overcomes signal contamination from chemical interactions between biomolecules and the metal surface; it does this by coating the metal surface with an inert layer of alumina or silica. In the present contribution, the role and the applications of Raman, SERS and related spectroscopic techniques in the study of biomolecules in biomaterials are reviewed and discussed.

Further expanding versatility of surface-enhanced Raman spectroscopy: from non-traditional SERS-active to SERS-inactive substrates and single shell-isolated nanoparticle.

After surface-enhanced Raman spectroscopy (SERS) was initiated over four decades ago, its practical application seems to be far behind the fundamental research that has made tremendous progress. SERS as a highly sensitive technique has not been widely adopted by the materials science and surface science communities or in the market of analytical instruments. In this discussion, we first classify the previous approaches along this direction over the past four decades and divide them into three strategies. Based on our recent theoretical and experimental approaches, we discuss in more detail the third strategy related to shell-isolated nanostructures. It can significantly expand the SERS study on nontraditional SERS-active (i.e. weakly SERS-active) materials (e.g. Pt, Ni, Fe, etc.) and even SERS-inactive materials (e.g. Si and Al2O3). We then focus on a single shell-isolated nanoparticle and how to controllably locate the strong electromagnetic field just at the probe surface of various materials. The use of side illumination at a high incident angle and/or nanocubes can further enhance the Raman signal by one to two orders of magnitude, which could be helpful for quantitative studies for surface science, heterogeneous catalysis, and soft matter science.

Metal-enhanced fluorescence of single shell-isolated alloy metal nanoparticle.

A single silica-shell isolated Au-Ag alloy nanoparticle is used for investigating a metal-enhanced fluorescence effect. Well-dispersed alloy nanoparticles are prepared by the facile chemical method, and the property of local surface plasmon resonance is controlled by adjusting the metal component of the alloy and shell thickness. The distance dependence of fluorescence enhancement for a single Au-Ag alloy nanoparticle is studied systematically with different silica shell thickness ranging from 2 to 35nm. The isolation shell not only adjusts the distance between metal surface and fluorophore emitters but also improves the chemical stability of the metal particle.

Coupling shell-isolated nanoparticle enhanced Raman spectroscopy with paper chromatography for multi-components on-site analysis

By coupling shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) with paper chromatography, two birds with one stone method were developed for simultaneous on-site separation and optical detection of multiple components. The established method features high sensitivity of plasmon-enhanced sensing strategies and sufficient temporal and spatial resolution of planar chromatographic techniques.

Structure Sensitivity in Catalytic Hydrogenation at Platinum Surfaces Measured by Shell-Isolated Nanoparticle Enhanced Raman Spectroscopy (SHINERS)

The in situ combination of electrochemistry and shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) has been used for the first time to investigate the surface structure sensitivity of asymmetric catalytic hydrogenation at single-crystal Pt electrodes. The adsorption and hydrogenation behavior of aqueous ethyl pyruvate (EP) at a range of modified and unmodified Pt{hkl} electrodes was measured both by cyclic voltammetry and by recording Raman spectra at hydrogen evolution potentials. Two primary surface intermediates were observed, including the previously reported half-hydrogenation state (HHS), formed by addition of a hydrogen atom to the keto carbonyl group, as well as a new species identified as intact chemisorbed EP bound in a μ2(C,O) configuration. The relative populations of these two species were sensitive to the Pt surface structure; whereas the μ2(C,O) EP adsorbate was dominant at pristine Pt{111} and Pt{100}, the HHS was only observed at these electrodes after the introduction of d...

Electromagnetic Enhancement in Shell-Isolated Nanoparticle-Enhanced Raman Scattering from Gold Flat Surfaces

The electromagnetic (EM) enhancement in shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was systematically analyzed for the first time by using the three-dimensional finite difference time domain (3D-FDTD) method. Compared with a bare metallic nanoparticle directly contact to a gold flat surface, a hot spot with stronger EM enhancement occurs in the junction between silica shell-isolated nanoparticle and flat surface in SHINERS. The largest enhancement factors can be as high as 9 orders of magnitude. The exact locations of hot spots and their EM enhancement strongly depend on the thickness of the silica shell, with an optimal thickness of 1 or 2 nm under 633 nm laser excitation. The dependence of the EM enhancement on both particle size and silica shell thickness was also investigated. The results further demonstrate that the SHINERS should be useful as a general diagnostic tool for surface science.

Silicon dioxide covered Au and Ag nanoparticles for shell-isolated nanoparticle enhanced spectroscopies in the near-infrared

SHINERS and SHINEF from Ag@SiO2and Au@SiO2excited in the near-infrared are presented, with high enhancement factors, together to TEM/EDX evidences of silica coverage over Au and Au nanoparticles.

Reconstruction and electrochemical oxidation of Au(110) surface in 0.1 M H2SO4

Variations of the surface structure and composition of the Au(110) electrode during the formation/lifting of the surface reconstruction and during the surface oxidation/reduction in 0.1M aqueous sulfuric acid were studied by cyclic voltammetry, scanning tunneling microscopy and shell-isolated nanoparticle enhanced Raman spectroscopy. Annealing of the Au(110) electrode leads to a thermally-induced reconstruction formed by intermixed (1×3) and (1×2) phases. In a 0.1 M H2SO4 solution, the decrease of the potential of the atomically smooth Au(110)-(1×1) surface leads to the formation of a range of structures with increasing surface corrugation. The electrochemical oxidation of the Au(110) surface starts by the formation of anisotropic atomic rows of gold oxide. At higher potentials we observed a disordered structure of the surface gold oxide, similar to the one found for the Au(111) surface.

CO Oxidation on Pt(100): New Insights based on Combined Voltammetric, Microscopic and Spectroscopic Experiments

We present an experimental study of the CO electro-oxidation on Pt(100)-(1×1) electrodes employing electrochemical methods in combination with in situ scanning tunneling microscopy (STM) and shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS). We discussed the nature and stability of the active sites in the preignition region in the presence of dissolved CO (COb) and monitored substrate structure changes during the COb electro-oxidation process. We corroborated that the electro-oxidation kinetics is determined decisively by the history of CO adlayer formation. A new mechanism was proposed for Pt(100) electrode deactivation in the preignition region after excursion of electrode potential to COb ignition region. We believe that this mechanism takes place on Pt surfaces independently on their crystallographic orientation.

In Situ SHINERS at Electrochemical Single-Crystal Electrode/Electrolyte Interfaces: Tuning Preparation Strategies and Selected Applications

We have studied Au(55 nm)@SiO2 nanoparticles (NPs) on two low-index phases of gold and platinum single crystal electrodes in ClO4(-) and SO4(2-) ion-containing electrolytes by both electrochemical methods and in-situ shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS). We showed the blocking of the electrode with surfactants originating from the synthesis of as-prepared SHINERS NPs. We introduce an efficient procedure to overcome this problem, which provides a fundamental platform for the application of SHINERS in surface electrochemistry and beyond. Our method is based on a hydrogen evolution treatment of the SHINERS-NP-modified single-crystal surfaces. The reliability of our preparation strategy is demonstrated in electrochemical SHINERS experiments on the potential-controlled adsorption and phase formation of pyridine on Au(hkl) and Pt(hkl). We obtained high-quality Raman spectra on these well-defined and structurally carefully characterized single-crystal surfaces. The analysis of the characteristic A1 vibrational modes revealed perfect agreement with the interpretation of single-crystal voltammetric and chronoamperometric experiments. Our study demonstrates that the SHINERS protocol developed in this work qualifies this Raman method as a pioneering approach with unique opportunities for in situ structure and reactivity studies at well-defined electrochemical solid/liquid interfaces.

Portable Measurement System Based on Raman Spectroscopy

In this paper, the portable Raman spectroscopy measurement system is presented. The measurement system can detect the Raman spectrum of objects using the advanced technique called Shell-isolated Nanoparticle Enhanced Raman Spectroscopy (SHINERS). This technique used gold nanoparticles coated with a thin, uniform, fully enclosed and optically transparent shell of silica or alumina so that the gold core generates a large surface enhancement and the shell controls the distance of the core from the surface to be detected. Based on this technique, the measurement system is designed including three modules, optical module, mechanical module and electrical control module. This Raman spectroscopy measurement system is portable, and can be used to the inspection of food safety, drugs, explosives and environment pollutants.

Semi-hydrogenation of alkynes at single crystal, nanoparticle and biogenic nanoparticle surfaces: the role of defects in Lindlar-type catalysts and the origin of their selectivity

For the first time, the method of shell-isolated nanoparticle Raman spectroscopy (SHINERS) is used in combination with cyclic voltammetry (CV) and reactivity studies to investigate the adsorption behaviour of a series of three alkynes undergoing hydrogenation on nanoparticle, single crystal and bacteria/graphite-supported platinum surfaces. It is found that a strong association of alkynes with defect sites to produce a long-lived di-sigma/pi-alkene surface complex allows for deep hydrogenation of this intermediate to the alkane product. In contrast, when platinum surface defect sites are blocked by either bismuth or polyvinylpyrrolidone (PVP) (and thus leaving behind only Pt{111} terrace adsorption sites), large increases in selectivity to the semi-hydrogenation product are observed for all three alkynes. This finding is consistent with SHINERS collected from both well-ordered and roughened Pt{111} electrodes which revealed that the di-sigma/pi-bonded surface intermediate is hardly formed at all on Pt{111} unless defect sites are introduced via electrochemical roughening. As a general method of producing selective catalysts, the elimination of toxic heavy metals from Lindlar-type catalyst, used commonly in organic chemistry, and their replacement by more benign, organic species adsorbed at defect sites is discussed.

Investigating the effect of aging on transpassive behavior of Ni-based alloys in sulfuric acid with shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS)

The effect of high temperature aging on the electrochemical behavior of Ni superalloys has implications for their use in Generation IV nuclear reactors. Linear sweep voltammetry, shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS), and X-ray photoelectron spectroscopy (XPS) were used to interrogate the passivation layer formed on heat-treated and as-received samples of Inconel 617 and Haynes 230. Results demonstrate that heat treatment improves electrochemical corrosion resistance for both alloys. The improved electrochemical behavior is associated with differences in the spectra; specifically, the appearance of a mixed Cr(III/VI) oxide.

Experimental Confirmation of Local Field Enhancement Determining Far‐Field Measurements with Shell‐Isolated Silver Nanoparticles

The plasmonic enhancement of fl uorescence or scattering involves the same enhancement mechanism [ 1 ] which is governed by the local fi eld enhancements in nanostructures sustaining localized surface plasmon resonances (LSPR). [ 1a , 2 ] It is the localized fi eld enhancement that is responsible for surface-enhanced spectroscopic processes such as shell-isolated nanoparticle enhanced Raman scattering (SHINERS) [ 3 ]