Probing Ground-State Single-Electron Self-Exchange across a Molecule−Metal Interface

Abstract

We have probed single-molecule redox reaction dynamics of hemin (chloride) adsorbed on Ag nanoparticle surfaces by single-molecule surface-enhanced Raman spectroscopy (SMSERS) combined with spectroelectrochemistry. Redox reaction at the molecule/Ag interface is identified and probed by the prominent fluctuations of the Raman frequency of a specific vibrational mode, ν(4), which is a typical marker of the redox state of the iron center in a hemin molecule. On the basis of the autocorrelation and cross-correlation analysis of the single-molecule Raman spectral trajectories and the control measurements of single-molecule spectroelectochemistry and electrochemical STM, we suggest that the single-molecule redox reaction dynamics at the hemin-Ag interface is primarily driven by thermal fluctuations. The spontaneous fluctuation dynamics of the single-molecule redox reaction is measured under no external electric potential across the molecule-metal interfaces, which provides a novel and unique approach to characterize the interfacial electron transfer at the molecule-metal interfaces. Our demonstrated approaches are powerful for obtaining molecular coupling and dynamics involved in interfacial electron transfer processes. The new information obtained is critical for a further understanding, design, and manipulation of the charge transfer processes at the molecule-metal interface or metal-molecule-metal junctions, which are fundamental elements in single-molecule electronics, catalysis, and solar energy conversion.

Raman spectroscopy probing of redox states and mechanism of flavin coenzyme

“…The setups were carefully calibrated using a mercury lamp and cyclohexane before Raman measurements with a spectral resolution of 2 cm −1 . A CHI 600C electrochemical workstation was used for performing electrochemical control equipped with a homemade electro spectroscopic cell (working electrode: indium tin oxide (ITO)/glass cover glass; counter electrode: platinum wire; reference electrode: silver wire). The ~40‐μl solution of FMN (prepared in B‐R buffer and 0.4 M KCl) and silver nanoparticles are incubated overnight on the ITO surface and dried, then a solution of 0.1 M KCl was put on the top of the ITO as a supporting electrolyte in the homemade electroscopic cell.…”

In Situ Surface-Enhanced Raman Spectroelectrochemical Analysis System with a Hemin Modified Nanostructured Gold Surface

“…[11][12][13][14][15]28,29 The which indicates the partial oxidation of the iron cores on the surface. 18 For an applied potential of E=-0.5 V (Fig. 4(b)), a single vibration band is observed at ν 4 ≈1349 cm -1 , which lies in the reduced ferrous state range, thus indicating reduction of the iron 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 cores on the surface (see Table S2 in the supporting information for a tabulated list of the observed Raman bands).…”

“…[10][11][12][13][14][15][16][17][18][19] However, in most cases surface-enhanced resonance Raman scattering (SERRS), excited with high laser powers, is required in order to resolve small quantities of adsorbed species on the WE. [10][11][12][13][14][15][16][17] SERRS requires that the laser source wavelength is resonant with the surface plasmon resonance wavelength of the nanostructured metal surface as well as the electronic absorption band of the molecule of interest, thus SERRS spectroelectrochemistry is most often performed on Ag nanostructures, which are prone to oxidation in aqueous solutions.…”

Probing single molecules and molecular aggregates: Raman spectroscopic advances

“…The optimization of SMR systems may involve the use of orderly assembled Ag/Au nanoparticles and nano‐arrays, which can be obtained by nano‐transfer printing via electron beam lithography . Other periodically nanoparticle tetramer‐patterned substrates have also been reported . On optimized substrates, a concentration limitation up to ~10 −15 or ~10 −16 M has been attained for SMR observation of certain analytes .…”