Monitoring the Dynamic Process of Formation of Plasmonic Molecular Junctions during Single Nanoparticle Collisions

Abstract

The capability to study the dynamic formation of plasmonic molecular junction is of fundamental importance, and it will provide new insights into molecular electronics/plasmonics, single-entity electrochemistry, and nanooptoelectronics. Here, a facile method to form plasmonic molecular junctions is reported by utilizing single gold nanoparticle (NP) collision events at a highly curved gold nanoelectrode modified with a self-assembled monolayer. By using time-resolved electrochemical current measurement and surface-enhanced Raman scattering spectroscopy, the current changes and the evolution of interfacial chemical bonding are successfully observed in the newly formed molecular tunnel junctions during and after the gold NP "hit-n-stay" and "hit-n-run" collision events. The results lead to an in-depth understanding of the single NP motion and the associated molecular level changes during the formation of the plasmonic molecular junctions in a single NP collision event. This method also provides a new platform to study molecular changes at the single molecule level during electron transport in a dynamic molecular tunnel junction.

Direct Observation of Amide Bond Formation in a Plasmonic Nanocavity Triggered by Single Nanoparticle Collisions

“…As shown in the SEM image (Figure c), a number of Lomant-GNPs are discretely distributed on the surface of CA modified GNE apex, with a typical number density of 11.4/μm 2 after the collision experiment. This observation is in line with our previous observations, , where only a few GNPs were found at the GNE apex. The SERS signals are mainly due to molecules inside the “hotspot” of the NPoNE structure.…”

“…To further understand the dynamic interaction, and reaction, between the NHS ester and the amine groups during and after the collision process, we investigated the time-resolved SERS spectra recorded at the same time. ,, No detectable Raman signal could be observed before adding Lomant-GNPs (Supporting Information Figure S5b). The SERS time trajectory in Figure b reveals the spectral changes within the hotspot of NPoNE cavities immediately after adding the Lomant-GNPs.…”

“…However, little is known about quantitative means of measuring chemical bond formation in real time. This challenge can be tackled by high temporal resolution microspectroscopic techniques, as they can provide valuable chemical fingerprint information during the chemical reaction process. ,, Therefore, real-time observations of purely single-molecule transient reaction with associated unambiguous chemical structure identification, applicable to chemical bond formation in solution, remain exceptionally challenging. ,− …”

“…To achieve single-molecule level detection of chemical reaction, it is crucial to (i) obtain clear signals significantly above any background and to (ii) minimize instrument response time . In the past decade, surface enhanced Raman spectroscopy (SERS) has shown considerable promise for the detection of single-molecule behaviors in the heterogeneous chemical reactions in a plasmonic molecular junction. , Furthermore, the recent development of single-entity electrochemistry techniques also enables individual plasmonic nanoparticle (NP) collision events on a nanoelectrode (NE) to be investigated. − In addition to tracking of single NP dynamic motion and the sizing of individual NPs, the NP collision electrochemistry has been established as an effective strategy for (i) establishing intrinsic electrochemical parameters that describe the mechanism of redox processes and (ii) understanding electrochemical kinetics and interface charge transfer events, thus providing valuable additional information to that obtained using the conventional analysis. − The collision events of metallic NPs on metallic nanoelectrode result in the formation of dynamic plasmonic nanocavities in the nanoparticle-on-nanoelectrode (NPoNE) geometric configuration . The use of a nanoelectrode not only reduces the nanoparticle collision frequency in the in situ SERS experiments toward the reaction at the single-molecule level but also greatly decreases baseline noise, and this superior resolution offers an opportunity for monitoring chemical bond formation that approaches the single-molecule level.…”

“…It has been demonstrated that the well controlled electrochemical interface and confined space of a nanopore electrode provide a promising environment for evaluating chemical dynamics at the nanoscale. − Therefore, the simultaneous single-entity electrochemistry and SERS measurement system, designated as single-entity EC-SERS, can be a valuable tool to capture the detailed dynamic chemical changes during and after the formation of NPoNE geometry containing molecular junctions. In our recent works, ,, the dynamic changes induced by metal–molecule interactions, intermolecular hydrogen bonds, and host–guest interactions during and after the gold NP­(GNP) “hit-n-stay” and “hit-n-run” collision events on a chemically modified gold NE (GNE) have been probed with the single-entity EC-SERS techniques. These prior studies have led to an enhanced understanding of single NP dynamic motion near the molecule modified electrode surface and the associated molecular changes in the NPoNE structures.…”