DWCNT-Doped Silica Gel Exhibiting Both Ionic and Electronic Conductivities

Silica gels doped with double-walled carbon nanotubes (DWCNTs) were prepared using an aqueous sol–gel route in mild conditions (neutral pH, room temperature). The wet gels exhibited both ionic and electronic conduction. Electrochemical impedance spectroscopy was used to study these two different conduction pathways that prevail at different characteristic time scales. The ionic conduction in the silica network was found to be independent of the DWCNT-doping rate. The electronic conduction through the DWCNT network was found to occur above a critical concentration (0.175 wt %) corresponding to nanotube percolation threshold. The highest content in DWCNTs (0.8 wt %) exhibited a conductivity of 0.05 S/m. Furthermore, the DWCNTs network was found to evolve even after the macroscopic solidification of the gel, suggesting a reorganization of the DWCNTs at the molecular level. This phenomenon could be attributed to the polarization effect of the electrode and was confirmed by Raman spectroscopy studies. Such materials can be useful for the design of sensors incorporating electroactive chemical or biological species

Design of Stable Plasmonic Dimers in Solution: Importance of Nanorods Aging and Acidic Medium

We describe a simple and effective strategy to couple gold nanorods (GNRs) into end to end dimers and freeze the assembly in water. The assembly is initiated using cysteine and driven by hydrogen bonding between two cysteine. We show that the aging of GNRs samples impacts both the assembly kinetics and the final yield of GNRs dimers. The addition of an appropriate amount of silver nitrate induces the immediate termination of GNRs dimerization and stabilizes the small aggregates in solution for at least 24 h

Tailoring the Surface Chemistry of Gold Nanorods through Au–C/Ag–C Covalent Bonds Using Aryl Diazonium Salts

Tailoring the surface chemistry of gold nanorods is a key factor for successful applications in biology, catalysis, and sensing. Here, we report on the use of the diazonium salt chemistry for the functionalization of gold nanorods enabling the formation of strongly attached organic layers around the gold cores. The precise nature of the interface between the gold surface and the diazonium-derived aryl layers was probed by XPS, ToF-SIMS, SERS, and DFT. It was shown that the CTAB surfactant was partially exchanged by the diazonium salt which dediazonizes spontaneously to form Au–C covalent bonds with the surface. Interestingly, the silver used during the synthesis of gold nanorods and still present at their surface appears to be also involved in the grafting mechanism with Ag–C covalent bonds detected by ToF-SIMS. From this result, it is clear that the interfacial properties and reactivity of gold nanorods synthesized by the silver­(I)-assisted seed mediated growth approach are strongly influenced by the presence of silver

Discerning the Origins of the Amplitude Fluctuations in Dynamic Raman Nanospectroscopy

We introduce a novel experimental and analytical method for discerning rare surface-enhanced Raman scattering (SERS) events observable at the nanoscale. We show that the kinetics of the Raman activity recorded on an isolated nanostructure is punctuated by intense and rare events of large amplitude and spectral variations. The fluctuations of thousands of SERS spectra were analyzed statistically in terms of power density functions, and the occurrence of the rare events was quantified by a wavenumber statistics. Our analysis enables one to extract valuable and unique spectroscopic signature of Raman variations usually hidden in time-average or space-average measurements. We illustrate our approach using molecular surface dynamics of gold adatoms on nanoparticles