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Super-resolution microscopy has received a lot of interest in the past few years, culminating in the 2014 Nobel Prize in Chemistry for the development of the STED and STORM/PALM family of techniques. Around the same time, an interesting (and mischievously titled) commentary appeared in Nature Photonics, claiming to resolve (ho ho) a misconception about a third approach to super-resolution – SIM or ‘structured illumination microscopy’. This is a technique which can be used to improve the resolution by a factor of two. The paper argues that structured illumination microscopy only provides true resolution enhancement for fluorescence imaging and none at all for scattering imaging. This is despite recent papers making claims – and apparently providing experimental evidence – to the contrary.
Two of the key parameters that describe the performance of the optical microscope are its resolution and its field-of-view. In fact, these two parameters are coupled: switching to a higher magnification objective will improve the resolution, but also tend to reduce the field-of-view. This trade-off is encapsulated in the idea of the space-bandwidth product, which is (conceptually at least) a measure of how many useful pixels of information an imaging system can transmit. Typical microscopes and microscope objectives are limited to around 10 Megapixels; if we make these pixels smaller by increasing the resolution then the area covered must be reduced as well. So if we want to image large areas at high resolution, as we might want to do in histology for example, then we have to mechanically scan the slide underneath the microscope and stitch multiple images together.
Researchers at the University of Maryland have developed a low-cost fibre sensor for detecting blood flow. It has a diameter of just 125 microns, meaning it could be incorporated into a surgical instrument to alert the operator that they are approaching a blood vessel. It combines features of laser Doppler flowmetry and low coherence interferometry to provide a measurement with high spatial localisation, but without many of the complications of a full Doppler optical coherence tomography (OCT) system.