Coating gold nanorods with silica prevents the generation of reactive oxygen species under laser light irradiation for safe biomedical applications.

Gold nanoparticles can produce reactive oxygen species (ROS) under the action of ultrashort pulsed light. While beneficial for photodynamic therapy, this phenomenon is prohibitive for other biomedical applications such as imaging, photo-thermal drug release, or targeted gene delivery. Here, ROS are produced in water by irradiating gold nanorods and silica-coated gold nanorods with near-infrared femtosecond laser pulses and are detected using two fluorescent probes. Our results demonstrate that a dense silica shell around gold nanorods inhibits the formation of singlet oxygen (1O2) and hydroxyl radical (˙OH) efficiently. The silica coating prevents the Dexter energy transfer between the nanoparticles and 3O2, stopping thus the generation of 1O2. In addition, numerical simulations accounting for the use of ultrashort laser pulses show that the plasmonic field enhancement at the nanoparticle vicinity is lessened once adding the silica layer. With the multiphotonic ejection of electrons being also blocked, all the possible pathways for ROS production are hindered by adding the silica shell around gold nanorods, making them safer for a range of biomedical developments.

Influence of the Sequestration Effect of CTAB on the Biofunctionalization of Gold Nanorods.

Gold nanorods (GNRs) can be functionalized with multiple biomolecules allowing efficient cell targeting and delivery into specific cells. However, various issues have to be addressed prior to any clinical applications. They involve controlled biofunctionalization to be able to deliver a known dose of drug by immobilizing a known number of active molecules to GNRs while protecting their surface from degradation. The most widely used synthesis method of GNRs is seed-mediated growth. It requires the use of cetyltrimethylammonium bromide (CTAB) that acts as a strong capping agent stabilizing the colloidal solution. The problem is that not only is CTAB cytotoxic to most cells but it also induces the sequestration of biomolecules in solution during the functionalization steps of GNRs. The presence of CTAB therefore makes it difficult to control the immobilization of biomolecules to GNRs while removing CTAB from the colloidal solution, leading to the aggregation of GNRs. The sequestration effect of ssDNA in solution by CTAB was studied in detail as a function of the CTAB concentration and the nature of the solution (water or buffer) using Forster resonance energy transfer as a detection tool. The conditions in which DNA sequestration did and did not occur could be clearly defined. Using gel electrophoresis, we could demonstrate how strongly the ssDNA sequestration effect in solution impacts the GNR surface biofunctionalization.

An optimal architecture of magneto-plasmonic core-shell nanoparticles for potential photothermal applications.

In this work, the optical responses of Fe3O4@Au and Fe3O4@Ag are comprehensively investigated using the discrete dipole approximation. It is found that the resonance wavelength and absorption efficiency strongly depend on the composition of the core and shell, geometry of the nanoparticles, core to particle volume ratio, core radius and shell thickness. The strongest impact is due to the shell material, the shape of the nanoparticles and their combination. When the composition of the shell is changed from gold to silver, instead of one fundamental resonance peak the absorption spectrum shows two, corresponding to the bonding plasmon mode at the nanoparticle-environment interface and antibonding mode at the core-shell interface. The results also reveal a much higher tunability of the resonance wavelength as well as larger enhancement of the absorption efficiency as the spherical nanoparticle stretches to a prolate ellipsoidal shape. Furthermore, higher order plasmon modes appear in the absorption spectrum of prolate nanoparticles with a large aspect ratio. The existence of several plasmon modes together with wide tunability makes these nanoparticles good candidates for applications where two or more simultaneous absorption bands at different frequencies are required. These results might motivate experimentalists to optimize the synthesis of magnetic-plasmonic core-shell NPs in different applications as far as absorption is concerned.

Household aluminum foil matte and bright side reflectivity measurements: Application to a photobioreactor light concentrator design.

This work reports the design of a light concentrator intended to be used to cast uniform lighting over a photobioreactor. Household aluminum foils was chosen as reflective material to build the concentrator. This choice raised the question of which side to use. Thus measurements of household aluminum foil reflectivity spectra on both bright and matte sides were undergone. These measurements were done using an integrating sphere, over a 250-2500 nm range. Diffuse and total reflectivities were acquired, for two samples each time. The obtained results are very repeatable and in good agreement with literature on rolled aluminum sheets, for the bright side at least, as matte side data were not found. Specular reflectivity is higher for the bright side while diffuse reflectivity is higher for the matte one. Furthermore, both sides of the foil have the same total reflectivity, around 86 % in the visible range of the spectrum, 97% in the near infrared. Our measurements are readability usable and available as supplementary materials. Finally, we applied these findings to the in silico design of lab scale light concentrator illuminating a new photobioreactor. A modified version of the raytracing software Soltrace was used to determine which of the two sides of our household aluminum foil was be best suited for our application.

Hexacyano Ferrate (III) Reduction by Electron Transfer Induced by Plasmonic Catalysis on Gold Nanoparticles.

Redox reactions are of great importance in environmental catalysis. Gold nanoparticles (Au-NPs) have attracted much attention because of their catalytic activity and their localized surface plasmon resonance (LSPR). In the present study, we investigated, in detail, the reduction of ferricyanide (III) ion into a ferrocyanide (II) ion catalyzed by spherical gold nanoparticles of two different sizes, 15 nm and 30 nm, and excited at their LSPR band. Experiments were conducted in the presence (or absence) of sodium thiosulfate. This catalysis is enhanced in the presence of Au- NPs under visible light excitation. This reduction also takes place even without sodium thiosulfate. Our results demonstrate the implication of hot electrons in this reduction.

Pulsed-laser irradiation of multifunctional gold nanoshells to overcome trastuzumab resistance in HER2-overexpressing breast cancer.

BACKGROUND: HER2-overexpressing metastatic breast cancers are challenging practice in oncology when they become resistant to anti-HER2 therapies such as trastuzumab. In these clinical situations, HER2-overexpression persists in metastatic localizations, and can thus be used for active targeting using innovative therapeutic approaches. Functionalized gold nanoparticles with anti-HER2 antibody can be stimulated by near-infrared light to induce hyperthermia. METHODS: Here, hybrid anti-HER2 gold nanoshells were engineered for photothermal therapy to overcome trastuzumab resistance in HER2-overexpressing breast cancer xenografts. RESULTS: When gold nanoshells were administered in HER2-tumor xenografts, no toxicity was observed. A detailed pharmacokinetic study showed a time-dependent accumulation of gold nanoshells within the tumors, significantly greater with functionalized gold nanoshells at 72 h. This enabled us to optimize the treatment protocol and irradiate the mice when the anti-HER2 gold nanoshells had accumulated most in the tumors. After weekly injections of anti-HER2 gold nanoshells, and repeated irradiations with a femtosecond-pulsed laser over four weeks, tumor growth was significantly inhibited. Detailed tissue microscopic analyses showed that the tumor growth inhibition was due to an anti-angiogenic effect, coherent with a preferential distribution of the nanoshells in tumor microvessels. We also showed a direct tumor cell effect with apoptosis and inhibition of proliferation, coherent with an immune-mediated targeting of tumor cells by anti-HER2 nanoshells. CONCLUSION: This preclinical study thus supports the use of anti-HER2 gold nanoshells and photothermal therapy to overcome trastuzumab resistance in HER2-overexpressing breast cancer.

Raspberry-like small multicore gold nanostructures for efficient photothermal conversion in the first and second near-infrared windows.

Gold nanoraspberries were synthesized by a seed-mediated synthesis with polyethylene glycol-functionalized bisphosphonates. The original structure shifted the optical absorption to infrared, revealing very efficient photothermal properties within the 2nd biological transparency window and leading to cancer cell necrosis at moderate intracellular doses and low (safe) laser power.

Coupling localized plasmonic and photonic modes tailors and boosts ultrafast light modulation by gold nanoparticles.

Plasmonic nanoparticles offer a broad range of functionalities, owing to their ability to amplify light in the near-field or convert it into heat. However, their ultrafast nonlinear optical response remains too low to envisage all-optical high-rate photonic processing applications. Here, we tackle this challenge by coupling the localized plasmon mode in gold nanoparticles with a localized photonic mode in a 1D resonant cavity. Despite the nonradiative losses, we demonstrate that a strong, reversible, and ultrafast optical modulation can be achieved. By using a light pumping fluence of less than 1 mJ cm(-2), a change of signal transmittance of more than 100% is generated within a few picosecond time scale. The nanoparticle transient optical response is enhanced by a factor of 30 to 40 while its spectral profile is strongly sharpened. The large nonlinear response of such plasmonic cavities could open new opportunities for ultrafast light processing at the nanoscale.

Theoretical investigation of the off-axis z-scan technique for nonlinear optical refraction measurement.

The theoretical investigation of the off-axis z-scan technique for the measurement of nonlinear optical refraction in materials is presented. The normalized transmittance is calculated for different aperture radii and positions. The dependence of both the normalized transmittance amplitude (DeltaT(pv)) and the distance between maximum and minimum (Deltaz(pv)) on the aperture radius is analyzed. A condition for the applicability of the pinhole approximation is given.

Nonlinear optical absorption of ZnO doped with copper nanoparticles in the picosecond and nanosecond pulse laser field.

The nonlinear absorption of nanocomposite layers based on ZnO implanted with Cu+ ions with an energy of 160 keV in implantation doses of 10(16) and 10(17) ions/cm2 was investigated. The values of the nonlinear absorption coefficient were measured by the Z-scan method at a wavelength of 532 nm by use of nanosecond and picosecond laser pulses. Possible optical applications of these materials are discussed.