The investigation of proteins distribution at cellular membrane or the sensor surface is significant to elucidate the molecular mechanism in cellular biology and sensor fabrication. Label-free imaging analysis of protein has attracted much attention because of its simple analysis procedure and small disturbance to the measured system.Although various label-free technologies have been developed in recent years, there are still challenges in how to construct an imaging system with high sensitivity and simple equipment.
Recently, Jiang’s group developed a novel electrochemiluminescence (ECL)-based capacitance microscopy based on the long-term accumulation of ECL imaging, and successfully realized the label-free imaging of antigen on the electrode surface and on the plasma membrane of single cells.The core of this technology is that upon binding of protein on the electrode surface, the specific capacitance (Cs) in the binding region decreases. The decreased Cs is proposed to result in a relatively higher potential drop across the double layer (Vdl) in this region. Because the ECL intensity from luminol is highly dependent on the value of Vdl, higher Vdl values in the binding regions should induce brighter luminescence, which is distinguished from the surrounding surface. Eventually, the visualization of brighter ECL spots on the surface could reflect the binding of species in those regions without any labeling. Because of its advantages in high sensitivity, carcinoembryonic antigens (CEA) at electrode surface as low as ag (10-18 g) can be visualized. The setup is simple and contains only a common optical microscope, voltage generator and CCD camera. Further application of this approach permits the direct imaging of CEA antigens on single cells through the capacitance change after the formation of the antigen-antibody complex. Successful visualization of the analyte without any ECL tag will allow not only special capacitance microscopy for label-free bioassays but also a novel ECL detection approach for the sensitive detection of biomolecules.
Figure 1. Schematic illustration of the label-free visualization of antigens at the cellular membrane and the simplified Randles circuit.
This work was published in J. Am. Chem. Soc. 2019, DOI: 10.1021 / jacs.9b03007 as Electrochemiluminescence-based Capacitance Microscopy for Label-free Imaging of Antigens on the Cellular Plasma Membrane.Jingjing Zhang, a Ph.D. student, is the first author of this paper, and Professor Jiang is the corresponding author.Academician Hong-Yuan Chen gave important guidance to this work.This research was supported by the Ministry of Science and Technology of China（2016YFA0201200）、the National Natural Science Foundation of China (21327902) and the Excellent Research Program of Nanjing University (zyjh004).