LAUSR

without tagging. Of note, the X-ray tag showed enhanced photostability (almost no photo-bleaching after 10 frames of scans) compared to endogenous fluorescent tags (up to 28% decrease), which allowed repetitive scanning at high density and thus enabled imaging with high spatial and energy resolution. Furthermore, the XRM cell imaging based on this tagging system had approximately an order ofmagnitude improved spatial resolution (about 30 nm) when compared to the resolution of classic optical microscopy (about 200 nm). The authors demonstrated two important applications of this genetic tagging and X-ray imaging system: it can be used to image subtle changes and refined structures of intercellular connections, which remains challenging for optical microscopy and electron microscopy because of their resolution limits; and it can achieve multi-color X-ray imaging by introducing different peroxidase tags and DAB substrates containing elements with distinguishable adsorption energies. The work by the Fan and Zhu group provides a highly versatile platform technique for imaging targetedmolecules and structures in cells with high specificity and resolution. Importantly, as part of the ‘Synchrotron for Neuroscience—an Asia Pacific Strategic Enterprise’ (SYNAPSE) project, aiming to comprehensively map the neuronal network of the entire human brain, this genetically encodedX-ray tagging system can be adapted readily to visualize the neuron network at a subcellular level resolution.