Electron transfer is of great interest in many researches of basic chemical and biological phenomena, molecular electronics and energy materials. In particular, measurement of electron transfer at single-molecule level is critical to the in-situ study of biological processes.However, the detection limit is normally restricted in the picoampere to nanoampere range. It is highly desirable to develop a new electrochemical detection strategy avoiding above interferences. Prof. Zhu’s group recently published their new work titled with ‘Fermi level-tuned optics of graphene for attocoulomb-scale quantification of electron transfer at single gold nanoparticles’ in Nature Communications on 26 August.
In past few years, Prof. Zhu’s group has made many important progresses in the development of spatiotemporal resolution dark-field microscopy, and fabricated many biological analytical methods. They prepared Au@AgNRs nanoprobes for the tracing of entire autophagy processes at single-cell level (J. Am. Chem. Soc. 2015, 137, 1903-1908). They also developed a plasmonic-based thermal microscopy (ACS Nano 2015, 9, 11574-11581). In addition, Prof. Zhu’s group generated a spatiotemporal spectral imaging system to measure the sub-cellular temperature change (Nat. Commun. 2017, 8, 1498). Otherwise, they fabricated a co-axial dual-objective microscope to measure the hybridization events of single miRNA molecules (Nano Lett. 2018, 18, 3759-3765).
Recently, Prof. Zhu’s group developed a graphene-based electrochemical microscopy (GEM) with a home-made TIRF dark-field microscope. As shown in Figure 1, The optical signal of electron transfer arises from the Fermi level-tuned Rayleigh scattering of graphene, which is further enhanced by immobilized gold nanostars. Owing to the specific response to surface charged carriers, GEM enables an attoampere-scale detection limit of faraday current at multiple individual gold nanoelectrodes simultaneously. Our Ph.D student Qing Xia and associate research fellow Dr. Zixuan Chen are co-first authors of this work. Prof. Zhu is the corresponding author. Sir Hong-Yuan Chen and Prof. Jian-Rong Zhang advised this work. This research is supported by the National Natural Science Foundation of China.
Figure 1 (a) Schematic illustration of the construction of electrochemical cell, where WE, RE, and CE are working electrode, reference, and counter electrodes, respectively. A graphene layer is transferred onto a gold-coated cover slide with a 4-mm-diameter hole in center, on which attaching a 3.5-mm-diameter PDMS electrochemical cell to avoid reactions on the gold film. (b)Schematic illustration of the total internal reflection dark-field microscope. (c)Introduction of excess charges doping in the graphene layer with hydroxyl and hydroxonium ions. Insets show the corresponding energy diagrams. (d) Scanning transmission electron microscopy imaging of a gold nanostar with adsorbed cytochrome c. Scale bar is 50 nm. (e) Current density imaging of multiple gold nanostars with and without (open circles) cytochrome c modification at 0.16 V during continuous cycling of the potential between −0.4 V and 0.5 V at a rate of 0.1 V s−1. Scale bar is 5 μm. (f)cyclic voltammograms of a single gold nanostar with cytochrome c modification. The electrolyte is 70 mM PBS (pH 7.0) and the scan rate is 0.01 V s−1. (g) Scattering imaging of gold nanostars in e, where open circles indicate the location of gold nanostars without cytochrome c modification. Scale bar is 5 μm.
Paper Link：https://www.nature.com/articles/s41467-019-11816-3