In situ SERS monitoring of plasmon-driven catalytic reaction on gap-controlled Ag nanoparticle arrays under 785 nm irradiation

Plasmon-enhanced photocatalysis has attracted considerable attention due to its low energy consumption and high energy throughput. Surface-enhanced Raman scattering (SERS) is a highly sensitive and label-free nondestructive tool to investigate plasmon-driven photocatalytic reactions. Herein, we present a facile method to fabricate gap-controlled Ag nanoparticle (NP) arrays with uniform and high-density distribution of hot spots, which can be employed as both efficient plasmonic photocatalysts and stable SERS platforms. The plasmon-driven catalytic reaction of 4-nitrobenzenethiol (4NBT), which transforms it into p, p'-dimercaptoazobenzene (DMAB), is detected by using an in situ SERS technique at the excited wavelength of 785 nm. According to the temperature and laser power density dependent photocatalytic reaction rates observed on the Ag NP arrays, we quantitatively determined that the reductive coupling of 4NBT is more likely to occur as the gap decreases. The finite-difference time-domain (FDTD) simulation results demonstrate that the plasmonic hot spots are significantly enhanced with a decrease in gap, which in turn reduces activation energy. The gap-controlled Ag NP arrays are efficient for both promotion and detection of plasmon-driven catalytic reactions, and may pave a pathway for implementing efficient plasmonic photocatalytic platforms.

Polarization- and Angular-Resolved Optical Response of Molecules on Anisotropic Plasmonic Nanostructures

A sometimes overlooked degree of freedom in the design of many spectroscopic (mainly Raman) experiments involve the choice of experimental geometry and polarization arrangement used. Although these aspects usually play a rather minor role, their neglect may result in a misinterpretation of the experimental results. It is well known that polarization- and/or angular- resolved spectroscopic experiments allow one to classify the symmetry of the vibrations involved or the molecular orientation with respect to a smooth surface. However, very low detection limits in surface-enhancing spectroscopic techniques are often accompanied by a complete or partial loss of this detailed information. In this review, we will try to elucidate the extent to which this approach can be generalized for molecules adsorbed on plasmonic nanostructures. We will provide a detailed summary of the state-of-the-art experimental findings for a range of plasmonic platforms used in the last ~ 15 years. Possible implications on the design of plasmon-based molecular sensors for maximum signal enhancement will also be discussed.

Synthesis, characterization and application of TiO2/Ag recyclable SERS substrates

In this paper, rutile and anatase TiO₂/Ag nanocomposites were prepared by a facile and green photochemical method.