Super-resolution fluorescence dipole orientation microscopy

Super-resolution microscopy such as STED [1, 2], SSIM [3], or PALM/STORM [4] placed their respective critical requirements on the fluorescent labeling, thereby limits their applications in biology. Polarization as the fourth dimension of fluorescence can also provide intensity modulation, yet without the restriction to specific fluorophores. Here we present a new technique termed super-resolution dipole orientation mapping (SDOM), to extract the dipole orientation information beyond super-resolution imaging [5]. In SDOM, a polarization-variant model is established, in which the intensity determines the super-resolution microscopic image, whilst the phase determines the effective dipole orientation of each super-resolved focal volume. The dipole orientation mapping as a new dimension can be superimposed onto the super-resolution image. As fluorescent dipole orientation is an inherent feature of fluorecence, all kinds of fluroescent labels can be used in SDOM. With the dipole orientation information, we found that the membranes of spine neck in the opposite direction of the dendritic spine show very different polarization angles. A series of biological specimen have been studied with SDOM. This work brings a new dimension to super-resolution. It also bridges the fluorescent polarization microscopy (FPM) and fluorescence super-resolution microscopy together, to enable a deeper understanding of the fluorescent label and underlying biological structural information.