Room-Temperature Molecular Manipulation via Plasmonic Trapping at Electrified Interfaces

Abstract

For the motion control of individual molecules at room temperature, optical tweezers could be one of the best approaches to realize desirable selectivity with high resolution in time and space. Because of physical limitations due to the thermal fluctuation, optical manipulation of small molecules at room temperature is still a challenging subject. The difficulty of the manipulation also emerged from the variation of molecular polarizability depending on the choice of molecules as well as the molecular orientation to the optical field. In this article, we have demonstrated plasmonic optical trapping of small size molecules with less than 1 nm at the gap of a single metal nanodimer immersed in an electrolyte solution. In situ electrochemical surface-enhanced Raman scattering measurements prove that a plasmonic structure under electrochemical potential control realizes not only the selective molecular condensation but also the formation of unique mixed molecular phases which is distinct from those under a thermodynamic equilibrium. Through detailed analyses of optical trapping behavior, we established the methodology of plasmonic optical trapping to create the novel adsorption isotherm under applying an optical force at electrified interfaces.

Playing catch and release with single molecules: mechanistic insights into plasmon-controlled nanogaps

“…We can relate this fact to the displacement between the capture and release equilibrium. The anticorrelation between K ASS and K DIS under growing laser power densities, and their followed behaviour different from the reported by changing the captured molecule's concentration, lead us to think that the kinetic parameters deduced from the I(t ) readouts encompass primarily the SM capture and release processes, and disregard the involvement of surface and/or molecular transport, 18,28,60,82 processes out of the equilibrium.…”

“…17,24,25,66 This phenomenon has been attested by the observation of an increased probability of SM capture. 18,28 On the other hand, the nearfield gradient acts on the molecule trapped inside the nanogap and causes an angular motion of the molecule. [66][67][68] Due to the exerted torque on the molecular dipoles, 68 in a way that the molecular orientation is aligned along the field vector perpendicular to the nanogap axis, thus stabilising the SM junction optomechanically.…”

Single-Molecule Surface-Enhanced Raman Spectroscopy

“…On the one hand, the Brownian motion of molecules in the hotspot induces spectral fluctuations. Delicate single-molecule manipulation techniques are required to localize molecules to the same position of the hotspot or even drive molecules stepwise through the hotspot [110,115,116]. On the other hand, fabrication of SM-SERS substrates is also important to obtain highreproducibility substrates.…”

Single-Molecule Raman Spectroscopy of a Pentacene Derivative Adsorbed on the Nonflat Surface of a Metallic Tip

“…This observation is understood as a result of additional resonance enhancement of the relevant Raman transition associated with a specific charge transfer interaction (or electronic hybridization) between the metal and adsorbate, and it is known as the chemical mechanism of SERS . Through these mechanisms, the Raman enhancement factor can be as large as 10 6 –10 8 , , which enables us to obtain the structural information about trace amounts of molecules adsorbed on a nanocontoured substrate or dispersed nanoparticles. − …”