Cell junctions are protein structures located at specific cell membrane domains that determine key processes in multicellular development. Here we report spatially selective imaging of cell junctions by electrochemiluminescence (ECL) microscopy. By regulating the concentrations of luminophore and/or co-reactant, the thickness of ECL layer can be controlled to match with the spatial location of different cell junctions. At a low concentration of luminophore, ECL generation is confined to the electrode surface, thus revealing only cell-matrix adhesions at the bottom of cells. While at a high concentration of luminophore, the ECL layer can be remarkably extended by decreasing the co-reactant concentration, thus allowing the sequential imaging of cell-matrix and cell-cell junctions at the bottom and near the apical surface of cells, respectively. This strategy not only provides new insights into the ECL mechanisms but also promises wide applications of ECL microscopy in bioimaging.Cell junctions are specific domains on the cell membrane that tether cells to the extracellular matrix or connect the lateral surfaces of adjacent cells. [1] The junctions located at the bottom of basal cell membrane are called cell-matrix adhesions, while those near the apical surface of cell are termed as cell-cell junctions. [2] They are not only responsible for the physical integration of individual cells to threedimensional tissues, [3] but also regulate a variety of biological processes in multicellular organisms, such as neuronal pathfinding, embryonic development, cancer invasion and metastasis. [4] Although cell junctions have distinct structures and functions, they are all involved in a continuous crosstalk. [5] Knowing precisely how cell-matrix and cell-cell junctions are distributed in the cellular structure is critical for understanding their functions and associated biological events. Surfacesensitive methods such as interference reflection, [6] total internal reflection fluorescence [7] and surface plasmon resonance microscopies [8] have been used in mapping cell-matrix adhesions, while electron microscopy and fluorescence microscopy (in particular confocal laser scanning microscopy, CLSM) are the most frequently used methods for imaging cell-cell junctions, [9] which however often require expensive facilities or specific immunofluorescent labelling.
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