Increases resolution by exploiting interference patterns created when two grids are overlaid at an angle
In SIM imaging resolution is increased by exploiting interference patterns (moiré patterns) when two grids are overlaid at an angle. Moiré patterns can be distinguished under the microscope, even when one or both of the original ‘grids’ is too small to resolve. In SIM, one of the grids takes the form of structured excitation light (essentially strips of light similar to a barcode), while the other is the specimen’s unknown distribution of fluorescent probes. As the pattern of light illumination is structured and, therefore, known, it is possible to obtain information about the pattern of fluorescence in the sample from the moiré pattern, which can be used to create both 2-D and 3-D super-resolution images.
SIM provides a ~two-fold improvement in xyz resolution with minimal changes to standard indirect immunofluorescence sample preparation. With its ease of use and intrinsic optical sectioning properties, N-SIM is quickly becoming the imaging tool of choice for high resolution, multi-channel imaging, 3D imaging. SIM imaging can also be applied to living, moving specimens enabling the observation of, for example, mitochondrial dynamics in living cells.
Nikon’s N-SIM imaging system (available through a license agreement with the University of California, San Francisco Office of Technology Management for Structured Illumination Microscopy) is based on the Eclipse Ti inverted research level microscope with Perfect Focus System (PFS) and CFI Apo TIRF 100x oil objective lens (N.A. 1.49).