Catalytic Hot-Electron SERS Analytical Substrates and a Case Study on Graphene Nanocomposite Inspection

Abstract

Hot-electron transfer between an electrode surface and an adsorbate is potentially useful in numerous electrochemical technologies, especially those operating at room temperature. Although challenging, estimation of the parameters controlling such a transfer process is fundamentally important to electrode design and utilization. Herein, nanothin Au/SiO2/Si electrodes are fabricated and analyzed for the source, generation, energetic characteristics, and interfacial transfer process of photogenerated surface hot electrons using excitation wavelength- and electron density-dependent Raman spectroscopy with methylene blue (MB) as the target molecule. Although Raman signal intensity exponentially increases with Si doping concentration when illuminated by a green laser, the signal intensification appears constant for a red laser. In both cases, Raman enhancement factors follow catalytic degradation with increasing measurement cycles. In conjunction with the calculated density of state distribution of the MB/Au interface, the observed Raman signals are ascribed to the charge-transfer (CT) surface-enhanced Raman scattering (SERS) mechanism, induced by the indirect and the resonant surface plasmon-enhanced direct interfacial transfers of hot electrons originating from Si and Au when excited by green and red lasers, respectively. Applying the electrodes as a CT SERS platform based on the above information to inspect a reduced graphene oxide/silica (rGO/SiO2) nanocomposite, conducting rGO core/insulating SiO2 shell structure, which implies plasmonic-heating property, is proposed and correlated with its photothermal efficiency. The findings shed light on the applicability of the hot-electron injector not only for molecular analysis but also for relevant technologies such as photoelectrocatalysis.

Coupling Au-loaded magnetic frameworks to photonic crystal for the improvement of photothermal heating effect in SERS

“…Next, the ascorbic acid solution was added to a mixture of HAuCl 4 $3H 2 O solution and CTAB (20 mM) at 35 °C for 0.5 h, followed by the addition of the Au seed solution to obtain a solution of Au NPs (100 mL) with good dispersion. The prepared colloidal Au solutions (10,15,20,25,30,40, and 50 mL) were added to the silica suspension (50 mL) under ultrasonic dispersion for 1 h, respectively. Next, based on the vertical deposition method, clean glass slides were vertically introduced into these mixtures, respectively, and evaporated at 55 °C for 3 h. Finally, the Au-PC lms with different amounts of Au NPs were obtained on the surface of the glass slides by selfassembly.…”

“…[6][7][8][9][10][11][12][13][14] Recently, numerous researchers have reported the potential role of the photothermal heating effect in SERS studies, however, the results are mixed. [15][16][17][18][19][20][21][22][23][24] For example, mild photothermal heating plays a positive role in SERS and has been widely employed in the eld of optical sensing and biological imaging. 25 On the other hand, the heat-induced degradation of analytes can produce carbonaceous species, cause desorption of the adsorbates in the excitation area, and lead to the catalytic transformation of analytes to produce other species.…”