  Over the past decade, structured illumination microscopy (SIM) has found its
niche in super-resolution (SR) microscopy due to its fast imaging speed and low
excitation intensity. However, due to the significantly higher light dose
compared to wide-field microscopy and the time-consuming post-processing
procedures, long-term, real-time, super-resolution observation of living cells
is still out of reach for most SIM setups, which inevitably limits its routine
use by cell biologists. Here, we describe square lattice SIM (SL-SIM) for
long-duration live cell imaging by using the square lattice optical field as
illumination, which allows continuous super-resolved observation over long
periods of time. In addition, by extending the previous joint spatial-frequency
reconstruction concept to SL-SIM, a high-speed reconstruction strategy is
validated in the GPU environment, whose reconstruction time is even shorter
than image acquisition time, thus enabling real-time observation. We have
demonstrated the potential of SL-SIM on various biological applications,
ranging from microtubule cytoskeleton dynamics to the interactions of
mitochondrial cristae and DNAs in COS7 cells. The inherent lower light dose and
user-friendly workflow of the SL-SIM could help make long-duration, real-time
and super-resolved observations accessible to biological laboratories.
