Chitosan-Capped Au Nanoparticles for Laser Photothermal Ablation Therapy: UV-Vis Characterization and Optothermal Performances

We have reported on the synthesis and characterization of near-infrared- (NIR-) absorbing colloidal nanoparticles prepared by exploiting the one-step reaction of HAuCl4 and Na2S2O3, followed by their stabilization with chitosan. This reaction also produces a big amount of unwanted nanoparticles detuned with respect to the NIR spectral region. For this reason, it is usually assumed that the product has to be filtered and enriched to enhance its NIR absorption, and the possible exploitation of the simpler raw product has never been worthy to be considered. Aiming to investigate this missing aspect, we chose to avoid the purification steps and rather focused on the preparation of the unrefined colloid, identifying the synthesis conditions that maximize its NIR absorbance and, subsequently, testing it as an optothermal transducer by measuring its molar heating rate (MHR). As expected, we found that the performances of the raw colloid are indeed lower than those of its refined version, but only to a limited extent. Moreover, MHR is unexpectedly higher than that deducible for other classical NIR-absorbing nanoparticles, like Au nanorods or Au nanostars. Thus, the product of the simpler preparation protocol appears as a competitive trade-off solution between easy manufacturing and optothermal performances

All optical switches based on the coupling of surface plasmon polaritons

We studied the potentials of All Optical Switches (AOS) based on the intensity-dependent coupling and decoupling of light into the SPP modes (Surface Plasmon Polaritons) of a sinusoidally corrugated thin metal film (TMF), due to Kerr induced refractive index changes of the surrounding dielectrics. The ideal device has two spatially separated outputs, collecting the reflected and transmitted light and the active volume can be as small as 10(-2) mm(3). Gold and PTS (poly-(2,4-hexadiyne-1,6-diol bis(p-toluene sulfonate) are the materials considered. Losses are limited to 1.5 dB,while a 20 dB extinction ratio per gate has been theoretically demonstrated with signal pulsewidths of 5-10 ps , using a maximum optical switching peak power of 11 kW

Switchable lensed linear micro axicon in plasmonic structures for all optical light processing

We propose a simple route to build up Fresnel bi-mirror microaxicons based on the localized absorption of an astigmatic pump laser beam by a plasmonic metal foil. The corresponding local overheating produces two main effects: the thermal swelling of the glass and the local increase of its refractive index. As a result, a two-mirrors axicon-like element coupled to a gradient index microlens is produced. We modelled the optothermal formation of this microelement by Finite Element Modeling and tested the predicted temperature raise by Scanning Thermal Microscopy (SThM). We calculated and measured the far field distribution of an impinging probe beam that passes through the lensed microaxicon, finding in both cases a noticeable change in the far field pattern when the pumping light is ON evidencing at the same time the good modulation capability of this opto-thermal element. A similar, even if smaller, effect was also found when the probe light impinges from the air side, where no gradient index region is present. This configuration allowed us to measure and confirm the theoretically expected angular deflection and, indirectly, the high value of the vertical thermomechanical deformation induced by the tight astigmatic focusing of the pump beam

Synthesis and Modelling of Gold Nanostars with Tunable Morphology and Extinction Spectrum

We present a simple seed-less synthesis procedure to fabricate stable gold nanostars (AuNSs) with tunable extinction properties from the visible up to 1800 nm, depending on the average values of core size and branch length. The experimental results are compared with data from Finite Elements Method computations by using an approximated model of the fabricated branched systems. The theoretical computations highlight the existence of hot spots located on the tips of the nanostars even up to 1800 nm wavelength, which opens the way to the improvement of IR diagnostics or chemical sensing

The Binding of EGFR to GM1(3) Hosted in Lipid Raft-Like Biomembranes Insighted by Plasmonic Resonance Techniques

We exploit Au/SiO2 plasmonic structures to check the effective binding activity of GM1(3) gangliosides hosted in physiological-like biomembranes, in presence of the Epidermal Growth Factor Receptor (EGFR). To this aim, we used bilayers that support the propagation of optical surface plasmon modes (plasmonic transducers, PTs) or guided modes (Plasmon Waveguide Resonators, PWRs). First, we measured the binding of EGFR to GM1(3) by using PTs. Indeed, effective interactions were evidenced, but with faint signals that prevented resolving dissociation kinetics. In order to enhance the optical responses, we turned our attention to PWRs. We first refined the design of a previously adopted Au/SiO2 PWR, finding that the nominal sensitivity is independent on SiO2 thickness but strongly dependent on its residual losses, due typically to a nonoptimal deposition process. We fabricated an improved Au/SiO2 resonator and tested the predicted signal enhancement by monitoring the binding of EGFR to GM3-enriched biomembranes. The measured signal was ~12-fold higher than that one measured using a PT, close to the maximum theoretical enhancement. The higher PWR response enabled us to detect the dissociation of EGFR from GM3, and the value of the apparent dissociation constant of the GM3-EGFR complex could be obtained

Langmuir-Blodgett films for waveguide nonlinear optics

Homogeneous and ordered thin films are necessary to fabricate nonlinear optical integrated devices. Langmuir-Blodgett technique may play a key role in the formation of ordered thin films of nonlinear optical organic materials. We investigated Langmuir Blodgett monolayers and thin films of the conjugated polymer poly3BCMU and the possibility of forming hybrid organic-glass integrated optical devices

Temperature sensing in EMD environment with periodically poled lithium niobate devices

A temperature sensor immune from electromagnetic noise is desgned and fabricated. The sensor key element is a periodiccally poled Lithium Niobate substrate