Laser-induced modification of polymeric beads coated with gold nanoparticles

Broadband Raman scattering enhancement with reduced heat generation in a dielectric-metal hybrid nanocavity

The strongly localized electric field achieved in metallic nanoparticles (NPs) and nanostructures are commonly employed to realize surface-enhanced Raman scattering. However, the heat originating from the Ohmic loss of metals may lead to the damage of the analyzed molecules, which severely limits the practical applications of pure-metallic nanostructures. Here, we propose a dielectric-metallic hybrid nanocavity placing silicon (Si) NPs onto a gold (Au) film to realize broadband Raman scattering enhancement with significantly reduced heat generation. Our results reveal that the heat generation is dramatically reduced in the hybrid nanocavity as compared with its pure-metallic counterpart while a significantly enhanced electric field is maintained. We demonstrate numerically and experimentally that the optical resonances, which arise from the coherent coupling of the electric and magnetic dipoles excited inside the Si NP with their mirror images arisen from the Au film, can be employed to enhance the excitation and radiation of Raman signals, respectively. We find that the enhancement in the radiation of Raman signals plays a crucial role in enhancing the total Raman scattering. We also show that the hybrid nanocavity acts as a nano-antenna which effectively radiates Raman signals into the far-field. These findings indicate the advantages of such hybrid nanocavities in temperature-sensitive Raman scattering characterization and supply new strategies for designing nanoscale photonic devices of other functionalities with hybrid nanocavities.

Stimuli-Responsive Phase Change Materials: Optical and Optoelectronic Applications

Stimuli-responsive materials offer a large variety of possibilities in fabrication of solid- state devices. Phase change materials (PCMs) undergo rapid and drastic changes of their optical properties upon switching from one crystallographic phase to another one. This peculiarity makes PCMs ideal candidates for a number of applications including sensors, active displays, photonic volatile and non-volatile memories for information storage and computer science and optoelectronic devices. This review analyzes different examples of PCMs, in particular germanium–antimonium tellurides and vanadium dioxide (VO₂) and their applications in the above-mentioned fields, with a detailed discussion on potential, limitations and challenges.

Photo-induced heat generation in non-plasmonic nanoantennas

The photo-induced heat generation in SiO₂/Si core/shell nanoantennas is analysed on the basis of their optothermal properties.

Spatial and Temporal Control of Information Storage in Cellulose by Chemically Activated Oscillations

Chemical oscillations are exploited to achieve self-expiring graphical information on paper-based supports with precise temporal and spatial control. Writing and self-erasing processes are chemically activated by exciting nonoscillating Belousov-Zhabotinsky (BZ) solutions infiltrated in cellulose paper filters. Exhausted supports can be reactivated many times by adding new BZ medium. Different parameters can be independently controlled to program mono- or multipaced information storage.

Photothermal healing of a glass fiber reinforced composite interface by gold nanoparticles

Scheme of interfacial healing process.

Thermo-Plasmonics for Localized Graphitization and Welding of Polymeric Nanofibers

There is a growing interest in modulating the temperature under the illumination of light. As a heat source, metal nanoparticles (NPs) have played an important role to pave the way for a new branch of plasmonics, i.e., thermo-plasmonics. While thermo-plasmonics have been well established in photo-thermal therapy, it has received comparatively less attention in materials science and chemistry. Here, we demonstrate the first proof of concept experiment of local chemistry and graphitization of metalized polymeric nanofibers through thermo-plasmonic effect. In particular, by tuning the plasmonic absorption of the nanohybrid through a change in the thickness of the deposited silver film on the fibers, the thermo-plasmonic effect can be adjusted in such a way that high enough temperature is generated enabling local welding and graphitization of the polymeric nanofibers.

Degradation of polypropylene carbonate through plasmonic heating

We report the thermal degradation of a solid film of polypropylene carbonate, driven by the photothermal effect of gold nanoparticles. We provide characterization of the products of this chemical reaction and use the known activation barrier for this chemical reaction to discuss the temperatures obtained in the film. In addition, we report the efficiency of the reaction as a function of nanoparticle concentration and find nanoparticles to be significantly more effective than an organic dye at driving this reaction.

Laser-induced cell detachment, patterning, and regrowth on gold nanoparticle functionalized surfaces

We report on the selective cell detachment from nanoengineered gold nanoparticle (AuNP) surfaces triggered by laser irradiation, which occurs in a nonthermal manner. The gold nanoparticle-based surfaces reveal good adhesion of NIH3T3 fibroblast cells. Patterning is achieved by lithographic microcontact printing, selective gold nanoparticle deposition, and by laser beam profiling. It is shown that the effectiveness of fibroblast cell detachment depends on the cell age, laser power, and AuNP patterning profile. Heat distribution and temperature rise around gold nanoparticle functionalized surfaces is modeled, revealing low heating of nanoparticles by laser illumination. The nonthermal photochemical mechanism of cell detachment due to production of reactive oxygen species under illumination of gold nanoparticles by green laser light is studied. We also demonstrate that cells migrate from unirradiated areas leading to their reattachment and surface recovery which is important for controlled spatial organization of cells in wound healing and tissue engineering. Research presented in this work is targeted at designing biointerfaces for cell cultures.

Nanoplasmonics for dual-molecule release through nanopores in the membrane of red blood cells

A nanoplasmonics-based opto-nanoporation method of creating nanopores upon laser illumination is applied for inducing diffusion and triggered release of small and large molecules from red blood cells (RBCs). The method is implemented using absorbing gold nanoparticle (Au-NP) aggregates on the membrane of loaded RBCs, which, upon near-IR laser light absorption, induce release of encapsulated molecules from selected cells. The binding of Au-NPs to RBCs is characterized by Raman spectroscopy. The process of release is driven by heating localized at nanoparticles, which impacts the permeability of the membrane by affecting the lipid bilayer and/or trans-membrane proteins. Localized heating and temperature rise around Au-NP aggregates is simulated and discussed. Research reported in this work is relevant for generating nanopores for biomolecule trafficking through polymeric and lipid membranes as well as cell membranes, while dual- and multi-molecule release is relevant for theragnostics and a wide range of therapies.

Recyclable SERS substrates based on Au-coated ZnO nanorods

Vertically aligned Au-coated ZnO nanorods (Au-ZnO NRs) were investigated as cheap, efficient and recyclable SERS-active substrates. The ZnO NRs were prepared through a simple, low-temperature hydrothermal route and made SERS-active through deposition of gold nanoislands by sputtering at room temperature. Optimized samples were able to detect methylene blue over a wide range of low concentrations (from 1 × 10(-4) to 1 × 10(-12) M), with good reproducibility. The photocatalytic properties of Au-ZnO NRs were exploited to recycle these substrates through UV-assisted cleaning. The experimental results showed that these substrates are characterized by high reproducibility and long shelf life, which make them promising as SERS platforms for multiple detection of different molecular species.

Using aggregates of gold nanorods in SER(R)S experiments: an empirical evaluation of some critical aspects

An empirical evaluation of some critical aspects resulting from aggregation of gold nanorods (AuNRs) used as surface enhanced resonant Raman scattering (SERRS)-active substrates was reported. Two types of AuNR substrates with longitudinal plasmon bands which either match (in-plasmon resonance) or not (off-plasmon resonance) the wavelength of the exciting laser source (λ: 632.8 nm) were tested in resonant Raman detection of methylene blue (MB). The in-plasmon resonance condition proved to be significantly useful for detecting MB at very low concentration (less than 10(-10) M), whereas the off-plasmon resonance setup is more than enough for intermediate-low concentrations (down to 10(-8) M). Differently sized AuNR aggregates, obtained by sequential dilution of the AuNR solutions allowed us to investigate the dependence of for surface enhanced Raman scattering (SERS) intensity on the size of the aggregates, pointing out a simple strategy for preparing AuNR-based SERS substrates.

Writing, self-healing, and self-erasing on conductive pressure-sensitive adhesives

A simple strategy for enabling conductive pressure sensitive adhesives (PSAs) to work as light-responsive materials is reported. Direct laser-writing of PSA substrates was achieved by means of a continuous-wave He-Ne laser focused through the objectives of an optical microscope. This approach takes advantage of cooperative interplay between viscoelastic properties of PSAs and enhanced thermal conductivity provided by an extra overlayer of gold. In particular, the thickness of the gold layer is a crucial parameter for tuning the substrate responsiveness. Self-healing and self-degradation processes can be exploited for controlling the lifetime of the written information, whereas additional protective coatings can be introduced to achieve permanent storage.

Excimer laser ablation of a Pt target in water: the observation of hollow particles

Micro/nanoparticles were fabricated by pulsed-excimer-laser ablation of a Pt target in water. Three kinds of hollow Pt particles (coalesced by micrograins, assembled by nanocrystals or with smooth shells) were observed together with solid particles using different laser fluences (2.3-6.8 J cm(-2)) and after 6000 laser shots. We propose that the hollow particles were formed on laser-produced bubbles which provided thermodynamically preferred nucleation sites and diffusion sinks for the laser-fabricated Pt clusters or particles. Although the hollow particles are a small proportion, the results have extended the scope of particles that pulsed-laser ablation in liquid can fabricate, and have enriched the mechanistic scenario of laser ablation and nanostructure formation in liquid.

Metal oxide microrings with femtoliter capacity for Raman microspectroscopy

A simple strategy, based on ultrafast heating of polystyrene microspheres infiltrated with a zinc acetate solution, is employed here for preparing ZnO microcontainers with femtoliter capacity. Their potential exploitation in micro-Raman assays for basic studies in bio- and nanotechnology is tested in different proof-of-concept experiments concerning the in situ analysis of l-glutathione crystals and gold-yeast cytochrome c bioconjugates. The ZnO microcontainers are also used as scaffolds for atomic layer deposition of TiO(2) overlayers with a fine-tuning of thickness and morphology. The resulting ZnO/TiO(2) heterostructures are tested in different photocatalytic experiments involving degradation and laser-induced conversion of methylene blue.

Using plasmonic heating of gold nanoparticles to generate local SER(R)S-active TiO2 spots

The plasmonic heating generated by laser irradiation of gold nanoparticles was exploited for fabricating SER(R)S-active anatase spots.