Photonic Crystals for Plasmonic Photocatalysis

Noble metal (NM)-modified wide-bandgap semiconductors with activity under visible light (Vis) irradiation, due to localized surface plasmon resonance (LSPR), known as plasmonic photocatalysts, have been intensively studied over the last few years. Despite the novelty of the topic, a large number of reports have already been published, discussing the optimal properties, synthesis methods and mechanism clarification. It has been proposed that both efficient light harvesting and charge carriers’ migration are detrimental for high and stable activity under Vis irradiation. Accordingly, photonic crystals (PCs) with photonic bandgap (PBG) and slow photon effects seem to be highly attractive for efficient use of incident photons. Therefore, the study on PCs-based plasmonic photocatalysts has been conducted, mainly on titania inverse opal (IO) modified with nanoparticles (NPs) of NM. Although, the research is quite new and only several reports have been published, it might be concluded that the matching between LSPR and PBG (especially at red edge) by tuning of NMNPs size and IO-void diameter, respectively, is the most crucial for the photocatalytic activity.

A 3D spongy flexible nanosheet array for on-site recyclable swabbing extraction and subsequent SERS analysis of thiram

A sponge inspired three dimensional flexible aluminum foil based ZnO nanosheet array substrate is described for use in real-world surface enhanced Raman spectroscopic detection. Gold and silver nanoparticles were employed to form numerous hot spots on uniformly grown ZnO nanosheets on the substrate. This flexible spongy substrate can extract analytes (such as the fungicide thiram) from various complex sample surfaces by physical swabbing. Specifically, this substrate was applied to detect thiram on the surface of fruits and vegetables. Non-destructive recycling detection with a relative standard deviation of 6.1% was accomplished by monitoring the characteristic Raman peak at 1382 cm^-1. This modified substrate has a low detection limit (0.2 ng cm^-2 of thiram for apple and tomato), outstanding uniformity (relative standard deviation = 8.9%) and thermal stability (relative standard deviation = 0.9%). Graphical abstract Schematic representation of using a aluminum foil modified with ZnO nanosheets as a flexible and recyclable substrate for SERS analysis of pollutants. The substrate can be cleaned after use by UV irradiation.

Non-Plasmonic SERS with Silicon: Is It Really Safe? New Insights into the Optothermal Properties of Core/Shell Microbeads

Silicon is one of the most interesting candidates for plasmon-free surface-enhaced Raman scattering (SERS), because of its high-refractive index and thermal stability. However, here we demonstrate that the alleged thermal stability of silicon nanoshells irradiated by conventional Raman laser cannot be taken for granted. We investigated the opto-thermal behavior of SiO₂/Si core/shell microbeads (Si-rex) irradiated with three common Raman laser sources (λ = 532, 633, 785 nm) under real working conditions. We obtained an experimental proof of the critical role played by bead size and aggregation in heat and light management, demonstrating that, in the case of strong opto-thermal coupling, the temperature can exceed that of the melting points of both core and shell components. In addition, we also show that weakly coupled beads can be utilized as stable substrates for plasmon-free SERS experiments.

Periodical 2D Photonic-Plasmonic Au/TiOx Nanocavity Resonators for Photoelectrochemical Applications

Effective light trapping at the nanoscale is vital for efficient photoelectrochemical (PEC) applications. Photonic and plasmonic resonators are the two most promising approaches for this purpose, and the synergetic combination of these two resonators will tail the propagation lengths of incident light along with field enhancements, and thus presents further enhanced light-trapping activity. Herein, a new hybrid photonic-plasmonic resonator is proposed through sputtering plasmonic Au nanoparticles (NPs) into the 2D photonic TiO_x nanocavity. Through facile control of the size of Au NPs, the matching of resonant wavelength of plasmonic Au NPs and photonic nanocavities maximize the light-trapping intensity and thus further improve the PEC performance. Furthermore, for expanding the PEC applications, after functionalization of Au NPs with aptamer as a biomolecular recognition unit, a PEC aptasensor is also proposed and presents the highest sensitivity for antibiotic detection.

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.

Triggering and monitoring plasmon-enhanced reactions by optical nanoantennas coupled to photocatalytic beads

Plasmonic metal/semiconductor nanocomposites promise to be a breakthrough for boosting and investigating photon-assisted processes at the nanoscale, with exciting perspectives for energy conversion and catalysis. However, the efficiency and selectivity of these surface processes are still far from being controlled. Here, shown for the first time, is a new class of photocatalyst which is based on the synergistic combination of bowtie-like gold nanoantennas and SiO2 /TiO2 core/shell oxide beads. These systems are exploited as efficient near-field optical light concentrators, stimulating photon-driven processes at the metal-semiconductor interface. Extraordinary enhancements of photodegradation rates (minutes instead of hours) result from matching the nanoantenna surface plasmon resonance with the optical absorption of organic dyes and the excitation source wavelength. Moreover, strong Raman enhancements are observed allowing for direct in-situ monitoring of reaction progress of different analytes on the same site.

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.

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.