Enhancing Raman Scattering without Plasmons: Unprecedented Sensitivity Achieved by TiO₂ Shell-Based Resonators

A remarkable enhancement of Raman scattering is achieved by TiO₂ shell-based spherical resonators in the absence of plasmonic enhancers. This effect is ascribed to the synergistic combination of high refractive index of the shell layer, multiple light scattering through the spheres, and related geometrical factors and can be exploited to fabricate a new generation of self-diagnostic, recyclable SERS-active substrates

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

Cavitands Endow All-Dielectric Beads With Selectivity for Plasmon-Free Enhanced Raman Detection of <i>N</i>_ε‑Methylated Lysine

SiO₂/TiO₂ microbeads (T-rex) are promising materials for plasmon-free surface-enhanced Raman scattering (SERS), offering several key advantages in biodiagnostics. In this paper we report the combination of T-rex beads with tetraphosphonate cavitands (Tiiii), which imparts selectivity toward <i>N</i>_ε<i>-</i>methylated lysine. SERS experiments demonstrated the efficiency and selectivity of the T-rex-Tiiii assays in detecting methylated lysine hydrochloride (<i>N</i>_ε<i>-</i>Me-Lys-Fmoc) from aqueous solutions, even in the presence of the parent Lys-Fmoc hydrochloride as interferent. The negative results obtained in control experiments using TSiiii ruled out any other form of surface recognition or preferential physisorption. MALDI-TOF analyses on the beads exposed to <i>N</i>_ε<i>-</i>Me-Lys-Fmoc revealed the presence of the Tiiii•<i>N</i>_ε<i>-</i>Me-Lys-Fmoc complex. Raman analyses based on the intensity ratio of <i>N</i>_ε<i>-</i>Me-Lys-Fmoc and cavitand-specific modes resulted in a dose–response plot, which allowed for estimating the concentration of <i>N</i>_ε<i>-</i>methylated lysine from initial solutions in the 1 × 10^–3 to 1 × 10^–5 M range. These results can set the basis for the development of new Raman assays for epigenetic diagnostics

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