Image scanning difference microscopy.

Here, we propose a novel imaging method, which is called image scanning difference microscopy (ISDM), for superresolution imaging. In ISDM, we implement a detector array composed of 19 avalanche photodiodes (APD) rather than single-point detector in standard confocal microscopy for reconstructing superresolved images with higher signal-to-noise ratio (SNR). Combining with our former proposed fluorescence emission difference (FED) method, we have achieved a lateral resolution of 111 nm (∼λ/6) without the damage of image quality, the highest FED resolution to the best of our knowledge. With its simple setup and remarkable performance, we believe that ISDM can become a versatile observation tool in biology and other fundamental studies. LAY DESCRIPTION: Fluorescence emission difference (FED) microscopy is a really simple and generalisable superresolved fluorescence microscopy method based on PSF engineering and difference algorithm recently. Compared to stimulated-emission-depletion fluorescence microscopy (STED), FED don't need complicated system or precise alignment and polarisation, available for wide variety of dyes and has low photobleaching and phototoxicity for living cells. However, the distortion caused by negative value is one of the biggest obstacles to the further development of FED. In light of this, we propose a novel superresolution imaging method based on the FED method with parallel detection system, which is called image scanning difference microscopy (ISDM). Our method has achieved a significant breakthrough in FED, increasing the resolution further while reducing artefacts generated by negative values, which cannot be accomplished through combining other methods. In addition, ISDM does not require complex setup and optical alignment, long time imaging and imposing no constraint on dyes. Importantly, we realised a transverse resolution of ∼λ/6 (triple diffraction limit) with single wavelength, single incident path and low light intensity, which has never been achieved in any other far-field superresolution microscopy.