Abstract:

In this study, a localized surface plasmon resonance (LSPR) fiber probe modified with Ag nanoparticles (NPs) was developed. The LSPR fiber probe not only serves as a reaction substrate for plasmonic catalysis, but also detects in situ surface-enhanced Raman spectroscopy (SERS) signals from the reaction product, thereby achieving the integration of the plasmonic catalysis reactions and SERS signal detection. To fabricate the LSPR probe, plasmonic Ag NPs were first self-assembled on the surface of the fiber probe with assistance by the amination and silanization of (3-aminopropyl) trimethoxysilane (APTMS) molecules. p-Aminothiophenol (PATP) was chosen as a model molecule for plasmonic catalytic reaction. By regulating the self-assembly time of the Ag NPs, a uniform distributed monolayer of Ag NPs was formed on the surface of the probe, with which excellent plasmonic catalysis effects and SERS signal collection from the reaction product of 4, 4′-dimercaptoazobenzene (DMAB) were achieved. It was found that the characteristic SERS signal of the plasmonic catalytic reaction product DMAB obtained from internal excitation and collection was 12.8 times more intense than that from the external excitation and collection under the same laser intensity conditions, demonstrating that the internal excitation and collection method was advantageous in the plasmonic catalysis and SERS signal detection. The LSPR fiber probe was demonstrably qualified to quantitatively detect the concentrations of PATP solutions in the concentration ranges 10⁻⁴–10⁻⁸ mol∙L⁻¹. Using the LSPR fiber probe, we also realized an in situ kinetics study of the PATP coupling reaction enhanced by plasmonic catalysis. The results showed that the Ag NP-based LSPR fiber probe with internal excitation and collection modes had the advantages of high sensitivity, low cost, facile preparation, and most importantly, applicability to in situ detection in a flexible manner with less damage to the samples. The preliminary study also indicated that it was feasible to combine the LSPR fiber probe with near-field scanning optical microscopy, not only to obtain morphological images of the surface but also to simultaneously perform the plasmonic catalysis reaction and the detection of micro-domains of the surface. This permitted the acquisition of a two-dimensional distributional assessment of surface reactions by the plasmonic catalysis.

Key words: Ag nanoparticles modified fiber probe, Plasmonic catalysis, Surface-enhanced Raman detection, p-Aminothiophenol, 4, 4′-Dimercaptoazobenzene