  Super-resolution optical microscopy is a rapidly evolving scientific field
dedicated to imaging sub-wavelength sized objects, leaving its mark in multiple
branches of biology and technology. While several super-resolution optical
microscopy methods have become a common tool in life science imaging, new
methods, supported by cutting-edge technology, continue to emerge. One rather
recent addition to the super-resolution toolbox, image scanning microscopy
(ISM), achieves an up to twofold lateral resolution enhancement in a robust and
straightforward manner. To further enhance ISM's resolution in all three
dimensions, we present and experimentally demonstrate here super-resolution
optical fluctuation image scanning microscopy (SOFISM). Measuring the
fluorescence fluctuation contrast in an ISM architecture, we obtain images with
a x2.5 lateral resolution beyond the diffraction limit along with an enhanced
axial resolution for a fixed cell sample labeled with commercially available
quantum dots. The inherent temporal averaging of the ISM technique enables
image acquisition of the fluctuation correlation contrast within millisecond
scale pixel dwell times. SOFISM can therefore offer a robust path to achieve
high resolution images within a slightly modified confocal microscope, using
standard fluorescent labels and within reasonable acquisition times.
