Imaging Spotlight


Calcium oxalate is frequently found in plants, leafy vegetable such as spinach, almonds and dates in the form of tiny needle like raphides. Whilst these play a central role in controlling calcium regulation, herbivory and metal detoxification, unfortunately if consumed, calcium oxalate can lead to kidney stones. Out of all the 3 forms of calcium oxalate, the monohydrate form is the one widely reported to cause kidney problems.

Images show needle like raphides of calcium oxalate crystals observed at Quorum Technologies using an Ultra high-resolution Field Emission Scanning Electron Microscope (FE-SEM), equipped with a PP3010 automated, column-mounted, gas-cooled cryo-preparation/ transfer stage chamber

Small cross-sections of the plants were cut and mounted on a universal cryo-stub using mounting media – a 50:50 mixture of Tissue-Tek OCT (Optimal Cutting Temperature) compound (Agar Scientific) and colloidal graphite (G303 Sakura) to fix and aid electrical conductivity.

The Tissue-Tek OCT (Optimal Cutting Temperature) being a mixture of clear water-soluble polyethylene glycol with polyvinyl alcohol and the colloidal graphite a mixture of graphite, propan‑2‑ol, butanol and 1-methoxy-2-propanol. The cryo-stub with sample was then mounted onto a specimen shuttle plunge frozen (vitrified) in slushed nitrogen (LN2) and transferred under vacuum conditions to the cryo-preparation chamber.

On the preparation cold stage, maintained at -140°C (anti-contaminator -175°C), the vitrified samples were cleaved with a cold knife, sublimated at -90°C for 2 – 3 min and then coated in situ with Iridium using a current of 5 mA for 60 – 90 s to ensure electrical conduction. Cryo-SEM imaging at -140°C (anti-contaminator -175°C) was carried out at acceleration voltages 1-1.5 kV and emission currents 15 – 20 µA at working distances 8 – 12 mm detecting secondary emitted electrons.
(Imaged by Dr Mark Taylor of Quorum Technologies, UK) #microscopy #Cryoprep #quorumtech #samplepreparation



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