Plasmonic heating assisted deposition of bare Au nanoparticles on titania nanoshells

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.

"RaMassays": Synergistic Enhancement of Plasmon-Free Raman Scattering and Mass Spectrometry for Multimodal Analysis of Small Molecules

SiO₂/TiO₂ core/shell (T-rex) beads were exploited as "all-in-one" building-block materials to create analytical assays that combine plasmon-free surface enhanced Raman scattering (SERS) and surface assisted laser desorption/ionization (SALDI) mass spectrometry (RaMassays). Such a multi-modal approach relies on the unique optical properties of T-rex beads, which are able to harvest and manage light in both UV and Vis range, making ionization and Raman scattering more efficient. RaMassays were successfully applied to the detection of small (molecular weight, M.W. <400 Da) molecules with a key relevance in biochemistry and pharmaceutical analysis. Caffeine and cocaine were utilized as molecular probes to test the combined SERS/SALDI response of RaMassays, showing excellent sensitivity and reproducibility. The differentiation between amphetamine/ephedrine and theophylline/theobromine couples demonstrated the synergistic reciprocal reinforcement of SERS and SALDI. Finally, the conversion of L-tyrosine in L-DOPA was utilized to probe RaMassays as analytical tools for characterizing reaction intermediates without introducing any spurious effects. RaMassays exhibit important advantages over plasmonic nanoparticles in terms of reproducibility, absence of interference and potential integration in multiplexed devices.

All-oxide Raman-active traps for light and matter: probing redox homeostasis model reactions in aqueous environment

Core-shell colloidal crystals can act as very efficient traps for light and analytes. Here it is shown that Raman-active probes can be achieved using SiO2-TiO2 core-shell beads. These systems are successfully tested in monitoring of glutathione redox cycle at physiological concentration in aqueous environment, without need of any interfering enhancers. These materials represent a promising alternative to conventional, metal-based SERS probes for investigating chemical and biochemical reactions under real working conditions.

Ordered array of gold semishells on TiO2 spheres: an ultrasensitive and recyclable SERS substrate

Ordered array of Au semishells on TiO(2) spheres with controlled size are prepared by combining the nanosphere self-assembly and atomic layer deposition (ALD). This ordered 2-D structure with designed array of metal nanogaps can be used as an ultrasensitive surface-enhanced Raman scattering (SERS) substrate with high reproducibility and stability. More importantly, the SERS substrates are recyclable, as enabled by their self-cleaning function due to the TiO(2) photocatalytic degradation of the target molecules. The high SERS sensitivity and recyclability are demonstrated by the detection of Rhodamine 6G (R6G) and brilliant cresyl blue (BCB) molecules. As both the nanosphere lithography and ALD are scalable processes, such 2-D ordered substrates may find applications in chemical sensing.

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.

Thermodynamics of optoplasmonic heating in fluid-filled gold-nanoparticle-plated capillaries

Dynamic and equilibrium thermal behavior of plasmon-heated gold/silica capillary nanocomposite during evaporative cooling by water or butanol is accurately described at centimeter length scales by continuum optoplasmonic thermodynamics for continuous-wave laser irradiation of 15-50 mW. Gold nanoparticles randomly distributed on the capillary via electroless plating exhibited a composite extinction cross section of 66.74 ± 0.72% of the area of the laser spot, more than 2-fold larger than the physical cross-section of the AuNPs. The extinction cross-section of the AuNPs capillary was invariant for incident laser powers of 15-150 mW and was reduced slightly in the presence of butanol and water due to absorption peak-shifting to lower energies. Introducing composite thermal parameters into the optoplasmonic thermodynamic relation extended its ability to predict heat transfer to laser powers of 100 and 150 mW for water and butanol, respectively. Nonlinear behaviors such as exponential thermal profiles caused by limited thermal conductivity and film boiling are identified at higher laser powers and prevent further extension of the relation. Mathematical reduction of temperature and time variables of the mathematical description shows it accounts for all measured thermodynamic effects when the aforementioned nonlinear behaviors are not present. This confirms that extraordinary thermal transport observed in some nanocomposites are absent for AuNP/silica systems in the given ranges, which allows a macroscale, continuum approach to describe thermal transport.