Matteo Martini

Shape effect on a single-nanoparticle-based plasmonic nanosensor

Plasmonic refractometric nanosensors based on single nanostructures, i.e. spherical, nanorodand bipyramid-shaped gold nanoparticles, are investigated and compared numerically by employing the finite-difference time-domain method. The results show that the plasmonic sensing ability is distributed anisotropically around the nanorod and bipyramid, even for spherical nanoparticles when the illumination light is linearly polarized. To optimize nanosensor performance, some anisotropy in the shape of nanoparticles is required, this latter serving as an intrinsic light polarization filter to suppress the disturbance from localized surface plasmon resonance in other directions. The plasmonic near-field can be engineered by controlling the shape to achieve a concentrated and localized electromagnetic field, in direct relation with the sensing ability. Taking these factors into account, the gold bipyramid nanoconstruct which is easily available in experiment is proposed as an efficient plasmonic sensing platform. The bipyramid presents both highly localized sensitivity and high scattering cross-section, thus avoiding the trade-off during the selection of the widely used nanorod-shaped sensors. The parameters of the bipyramid structure can be optimized by numerical simulation to improve the plasmonic sensing. Our findings permit a deeper understanding of single-nanoparticle-sensor behavior, and the study provides an opportunity to optimize the plasmonic sensor.

Suppression of luminescence quenching at the nanometer scale in Gd2O3 doped with Eu3+ or Tb3+: Systematic comparison between nanometric and macroscopic samples of life-time, quantum yield, radiative and non-radiative decay rates

By systematically studying the evolution of the optical properties with the content of some doping elements (Eu and Tb) in cubic gadolinium oxide, we demonstrated that the luminescence quenching could be almost entirely suppressed by elaboration of the samples in the nanometer range. Indeed, even if the proportion of quenchers (here surface hydroxyl groups) does increase at this scale, each rare-earth cation possesses an electronic configuration that depends on its distance from the surface and then slightly differs from that of the surrounding atoms. This difference almost eliminates any resonant transfer of excitation between all the atoms within the particle and suppresses a significant proportion of non-radiative losses. As a consequence, the quantum yield is not affected by the phenomenon of luminescence quenching because of concentration that is usually encountered in macroscopic samples. The emission can then be increased by a factor of about 3 for Tb and 5 for Eu simply by increasing the doping co...

One-Pot Synthesis of Hybrid Multifunctional Silica Nanoparticles with Tunable Coating by Click Chemistry in Reverse W/O Microemulsion

Multifunctional hybrid silica nanoparticles with a fluorescent core and tunable organic or polymeric shell can easily be prepared by a sol-gel process followed by 1,3 dipolar cycloaddition (CuAAC) in the same reverse quaternary W/O microemulsion. Compared to a classical multistep process, this one-pot synthesis reduces greatly the number of purification steps and avoids aggregation phenomena. The confinement of reactants inside the micellar system gives rise to a noticeable increase of the CuAAC reaction rate. In addition, using simultaneously two different substrates for CuAAC on silica allows us to obtain directly multifunctional hybrid nanoparticles displaying a double grafting without any separation or purification steps except the final recovery by centrifugation, which opens the door to a tunable coating of the nanoparticles. Particularly, the hydrophilic-lipophilic balance of the coating can be adjusted by implementing the pertinent MPEG:dodecyl azide ratio. As an application, the great versatility of this strategy has been proved by the one-pot synthesis of fluorescent silica nanoparticles with a PEG coating and encapsulating silver clusters.

Optimization of the synthesis of nanostructured Tb3+-doped Gd2O3 by in-situ luminescence following up

Nanostructured Tb(3+)-doped Gd(2)O(3) particles have been synthesized from chloride precursors by NaOH addition in a polyol medium. In-situ luminescent spectra have been investigated in order to follow up the process of formation and growth of these particles by varying parameters as the elaboration temperature and the rate of NaOH addition. Contrarily to all the literature related to the polyol synthesis, the paper proves that oxide particles can be directly formed at room temperature. These particles are also slightly bigger and organized in nanorods when NaOH is added progressively. Finally, it was found that the influence of further annealing up to 160 degrees C strongly depends on the NaOH addition rate. While preserving the oxide phase, annealing leads to bigger particles only in the case of a progressive addition of NaOH.

Testicular biodistribution of silica-gold nanoparticles after intramuscular injection in mice

With the continuing development of nanomaterials, the assessment of their potential impact on human health, and especially human reproductive toxicity, is a major issue. The testicular biodistribution of nanoparticles remains poorly studied. This study investigated whether gold-silica nanoparticles could be detected in mouse testes after intramuscular injection, with a particular focus on their ability to cross the blood–testis barrier. To that purpose, well-characterized 70-nm gold core–silica shell nanoparticles were used to ensure sensitive detection using high-resolution techniques. Testes were collected at different time points corresponding to spermatogenesis stages in mice. Transmission electron microscopy and confocal microscopy were used for nanoparticle detection, and nanoparticle quantification was performed by atomic emission spectroscopy. All these techniques showed that no particles were able to reach the testes. Results accorded with the normal histological appearance of testes even at 45xa0days post sacrifice. High-resolution techniques did not detect 70-nm silica-gold nanoparticles in mouse testes after intramuscular injection. These results are reassuring about the safety of nanoparticles with regard to male human reproduction, especially in the context of nanomedicine.

Strong two-photon fluorescence enhanced jointly by dipolar and quadrupolar modes of a single plasmonic nanostructure

A single gold nano-cylinder presenting multipolar plasmon resonances to enhance two-photon fluorescence is investigated employing three dimensional finite-difference time-domain method. Cylinders of large dimension usually display dipolar and quadrupolar plasmonic resonances. We demonstrate that the dipolar resonance can couple with the incident light resulting in a large localized field enhancement which increases the molecular excitation rate. At the same time, the radiative quadrupolar mode overlaps with the emission band of excited fluorophores to assist the fluorescence emission due to an enhancement in the quantum efficiency. Such dipole-quadrupole jointly enhanced two-photon fluorescence exhibits exceptionally promise in brighter label design.

A hybrid nanoantenna for highly enhanced directional spontaneous emission

Spontaneous emission modulated by a hybrid plasmonic nanoantenna has been investigated by employing finite-difference time-domain method. The hybrid nanoantenna configurations constituted by a gap hot-spot and of a plasmonic corrugated grating and a metal reflector sandwiching a SiO2 thin layer which appears promising for high spontaneous emission enhancement devices. Simulation assays show that the coupling between the gap-antenna and plasmonic corrugations reaches an ultra-high near-field enhancement factor in the excitation process. Moreover, concerning the emission process, the corrugations concentrate the far-field radiated power within a tiny angular volume, offering unprecedented collection efficiency. In the past decades, many kinds of optical antennas have been proposed and optimized to enhance single molecule detection. However, the excitation enhancement effect for single individual or dimmer plasmonic nanostructure is limited due to intrinsic nonradiative decay of the nanoparticle plasmon and ...

Enhanced chemiluminescence-based detection on gold substrate after electrografting of diazonium precursor-coated gold nanoparticles

Since it was demonstrated that nanostructured surfaces are more efficient for the detection based on the specific capture of analytes, there is a real need to develop strategies for grafting nanoparticles onto flat surfaces. Among the different routes for the functionalization of a surface, the reduction of diazonium salts appears very attractive for the covalent immobilization of nanoparticles because this method does not require a pre-treatment of the surface. For achieving this goal, gold nanoparticles coated by precursor of diazonium salts were synthesized by reduction of gold salt in presence of mercaptoaniline. These mercaptoaniline-coated gold nanoparticles (Au@MA) were successfully immobilized onto various conducting substrates (indium tin oxide (ITO), glassy carbon (GC) and gold electrodes with flat terraces) after addition of sodium nitrite at fixed potential. When applied onto the gold electrodes, such a grafting strategy led to an obvious enhancement of the luminescence of luminol used for the biodetection.

The Use of Fluorescent Tracers for Inhibitor Concentration Monitoring Useful for Scale Inhibitor Squeeze Evaluation

A common problem, in oilfield reservoirs is mineral scale deposition. The build-up of scale inside well bores and the surrounding reservoir causes millions of dollar in damage every year. The most common remedy is to treat the formation of such minerals with scale inhibitor chemicals in a “squeeze” treatment; which is performed periodically. One of the big challenges remains the real-time and on-site control of inhibitor concentration during production. A simple and accurate method to determine the concentration of inhibitors has been developed; this method is based on the use of luminescent tracers. The multiple lifetimes as well as the differences shown in the emission and excitation spectra of the tracers appear to be suitable for the luminescence detection. The increased signal to noise ration due to the suppression of the background resulting from the organic oil residues is used to measure the concentration of residual inhibitors in production waters. Furthermore, the use of a technique as versatile and simple as luminescence spectroscopy allows the online and/or on-site monitoring with very limited drawbacks. This paper describes the use of novel real-time scale inhibitor monitoring; this new technique will help to optimize the treatment rates of the scale inhibitor squeeze treatment.

Energy transfer from pyridine molecules towards europium cations contained in sub 5-nm Eu2O3 nanoparticles: Can a particle be an efficient multiple donor-acceptor system?

Sensitized Eu2O3 nanoparticles coated by polysiloxane have been prepared using a polyol method. Further grafting of pyridine molecules on particles surface enhances 400-times the emission of the Eu3+ cations. The sensitizing effect of the pyridine molecules that transfer a part of their excitation towards Eu3+ has been studied by systematic excitation and emission measurements. All of the de-excitation pathway rates involved in the emission processes of these nanoparticles were determined. In particular, the transfer efficiency which was found independent of the number of sensitizers per particle is equal to 0.13u2009±u20090.01, a value quite satisfying taking into account that the donors and the acceptors are separated by a polysiloxane spacer of 0.4u2009nm. Furthermore this multiple donor-acceptor system has been modeled in order to deduce the average transfer efficiency as a function of the single donor-acceptor transfer rate. The theoretical modeling is in complete coherence with the experiments performed on a se...