Plasmonic core shell bimetal nanoplates: A facile seeded-growth strategy is developed to prepare uniform plasmonic Pd@Ag core-shell bimetallic nanoplates. The as-prepared Pd@Ag nanoplates are not only uniform in both size and shape, but also display tunable SPR properties and significantly enhanced photothermal stability as compared with 2D pure-Ag nanostructures. They can thus be readily used as stable substrates for MR surface-enhanced Raman scattering and as NIR absorbers for photothermal cancer therapy.NSFC[21021061, 20925103, 20923004, 20871100]; Fok Ying Tung Education Foundation[121011]; MOST of China[2011CB932403, 2009CB930703]; NSF of Fujian Province[2009J06005]; Key Scientific Project of Fujian Province[2009HZ0002-1

Surface-enhanced Raman scattering (SERS) spectroscopy has attracted tremendous interests as a highly sensitive label-free tool. The local field produced by the excitation of localized surface plasmon resonances (LSPRs) dominates the overall enhancement of SERS. Such an electromagnetic enhancement is unfortunately accompanied by a strong modification in the relative intensity of the original Raman spectra, which highly distorts spectral features providing chemical information. Here we propose a robust method to retrieve the fingerprint of intrinsic chemical information from the SERS spectra. The method is established based on the finding that the SERS background originates from the LSPR-modulated photoluminescence, which contains the local field information shared also by SERS. We validate this concept of retrieval of intrinsic fingerprint information in well controlled single metallic nanoantennas of varying aspect ratios. We further demonstrate its unambiguity and generality in more complicated systems of tip-enhanced Raman spectroscopy (TERS) and SERS of silver nanoaggregates.

The surface plasmon resonance (SPR) induced photothermal and photoelectrocatalysis effects are crucial for catalytic reactions in many areas. However, it is still difficult to distinguish these two effects quantitatively. Here we used surface-enhanced Raman scattering (SERS) to detect the photothermal and photoelectrocatalytic effects induced by SPR from Au core Pt shell Nanoparticles (Au@Pt NPs), and calculated the quantitative contribution of the ratio of the photothermal and photoelectrocatalysis effects towards the catalytic activity. The photothermal effect on the nanoparticle surface after illumination is detected by SERS. The photoelectrocatalytic effect generated from SPR is proved by SERS with a probe molecule of p-aminothiophenol (PATP).

Surface-enhanced Raman spectroscopy (SERS) has attracted tremendous interest as a label-free highly sensitive analytical method. For optimization of SERS activity, it is highly important to systematically investigate the size effect of nanoparticles on the SERS enhancement, which appears to be challenging in experiment, as the localized surface plasmon resonance (LSPR) of nanoparticles also changes with the change of the particle size. This challenge can be overcome by utilizing the unique property of gold nanorods, whose LSPR wavelength can be controlled to be the same by properly choosing the size and aspect ratio of the nanorods. We obtained the correlated SEM images, scattering spectra, and SERS spectra on a home-built single nanoparticle spectroscopy system and systematically investigate the size effect on SERS of individual gold nanorods using the adsorbed malachite green isothiocyanate (MGITC) molecule as the probe molecule. The dark field scattering intensity was found to increase with the increase of the size of nanoparticles, whereas the SERS intensity increases with the decrease of the size as a result of the stronger lightning rod effect and weaker radiation damping. We further explored the size-dependent effect for the coupled nanorod dimer system. The SERS activity was also found to increase with a decrease of the particle size when the excitation is close to the LSPR wavelength. Understanding of the size effect on the local field enhancement may help to design and fabricate SERS substrate and TERS tips with high SERS activity.

Precise measurement of the temperature right at the surface of thermoplasmonic nanostructures is a grand challenge but extremely important for the photochemical reaction and photothermal therapy. We present here a method capable of measuring the surface temperature of plasmonic nanostructures with surface-enhanced Raman spectroscopy, which is not achievable by existing methods. We observe a sensitive shift of stretching vibration of a phenyl isocyanide molecule with temperature (0.232 cm −1 /°C) as a result of the temperaturedependent molecular orientation change. We develop this phenomenon into a method capable of measuring the surface temperature of Au nanoparticles (NPs) during plasmonic excitation, which is validated by monitoring the laser-induced desorption process of the adsorbed CO on Au NP surface. We further extend the method into a more demanding single living cell thermometry that requires a high spatial resolution, which allows us to successfully monitor the extracellular temperature distribution of a single living cell experiencing cold resistance and the intracellular temperature change during the calcium ion transport process.

Shell-isolated nanoparticles (NPs)-enhanced Raman spectroscopy (SHINERS) can be potentially applied to virtually any substrate type and morphology. How to take a step forward to prepare SHINERS NPs (SHINs) with superior performance is critical for the practical applications of surface-enhanced Raman scattering (SERS) in the breadth and depth. Here, we present a method to obtain 120 nm diameter gold NPs coated with ultrathin silica shells (1-4 nm). The silica shell can be controlled growth through carefully tuning a series of parameters, such as amount of 3-aminopropyl triethoxysilane used, pH, reaction time, and reaction temperature. We compare the enhancement factor of the obtained 120 nm Au with a 4 nm silica shell NPs to the 55 nm Au with a 4 nm silica shell NPs, and the activity of a 120 nm SHINs is nearly 24 times that the 55 nm SHIN from a single particle view. We also compare the enhancement factor of 1 nm silica shell Au@SiO 2 NPs with the bare Au NPs. The enhancement factor of 1 nm silica shell Au@SiO 2 NPs was found to be about twice that of the bare particles. For a deeper understanding of the source of the giant enhanced electrical field of the 1 nm silica shell Au@SiO 2 NPs, we study the plasmonic property of single 1 nm silica shell Au@SiO 2 NP on a gold film substrate through correlation of the structure of single NP using SEM with its SPR spectroscopy. We find that the multipolar interaction between the single Au@SiO 2 NP and gold film substrate is important for the SERS. Our studies on the performance of 120 nm SHINs and the plasmonic property of these particles can significantly expand the applications of SHINERS technique and improve the understanding of physical nature of SHINs.

Aiming to explore cooperative interactions between plasmonic metal and semiconductor nanostructures as well as their special plasmon resonant properties, we synthesized Au@Cu 2 O core−shell nanoparticles to demonstrate the dramatic influence of dielectric shell both experimentally and theoretically. The extinction spectra of Au@Cu 2 O nanoparticles with controllable shell thickness from a few layers to over 20 nm show not only a tunable red shift of resonant peak but also distinctive enhanced absorption intensity and peak splitting. We then built an analytical model based on an approximate Mie's theory to interpret their optical features. From this model, we found that the overall optical cross section and absorption portion of Au@Cu 2 O are dramatically enlarged. It has been shown that the proper dielectric shell-coated plasmonic nanoparticles could be very promising, especially for the applications that need effective enhancement of the plasmon resonant absorption.

A quantitative understanding of the localized surface plasmon resonances (LSPRs) of metallic nanostructures has received tremendous interest. However, most of the current studies are concentrated on theoretical calculation due to the difficulty in experimentally obtaining monodisperse discrete metallic nanostructures with high purity. In this work, endeavors to assemble symmetric and asymmetric gold nanoparticle (AuNP) dimer structures with exceptional purity are reported using a DNA self-assembly strategy through a one-step gel electrophoresis, which greatly facilitates the preparation process and improves the final purity. In the obtained Au nanodimers, the sizes of AuNPs (13, 20, and 40 nm) and the interparticle distances (5, 10, and 15 nm) are tunable. The size- and distance-dependent plasmon coupling of ensembles of single, isolated dimers in solution are subsequently investigated. The experimental measurements are correlated with the modeled plasmon optical properties of Au nanodimers, showing an expected resonance shift with changing particle sizes and interparticle distances. This new strategy of constructing monodisperse metallic nanodimers will be helpful for building more complicated nanostructures, and our theoretical and experimental understanding of the intrinsic dependence of plasmon property of metallic nanodimer on the sizes and interparticle distances will benefit the future investigation and exploitation of near-field plasmonic properties.