The Analytical Instrumentation Facility (AIF) at NC State has recently installed the CryoSEM JEOL JSM-7600. This FESEM, outfitted with Gatan Alto-2500 cryogenic transfer system and stage, can be used to evaluate hydrated samples without the need for drying. The CryoSEM is an ideal imaging tool for hydrated, beam sensitive, volatile and low melting point specimens that are normally difficult to image in traditional SEM. It can be widely used for botanical, biological, pharmaceutical, petrochemical, food, cosmetic, detergent and paint applications.
- 1 nm spatial resolution at 15 kV.
- 2 secondary and 1 backscatter electron detectors.
- 100eV- 30keV landing energy.
- 2 pot freezing station and vacuum transfer device.
- Alto-2500 delicate cryo-transfer and sample preparation chamber with built in cold knife fracture device and cold magnetron sputter coater.
- A high stability, gas-cooled cold stage module fitted to the SEM stage enabling vibration free SEM imaging under cryo-condition.
Advantages of Cryo-SEM
- Rapid freezing can preserve sample in its natural (hydrated) state.
- A soft, liquid or volatile sample is stabilized under the electron beam.
- Chemical fixation can be avoided.
- Fast freezing can maintain structural and cellular integrity.
- Freeze fracture and controlled freeze sublimation allow exposure of internal microstructure.
- Cryo-SEM sample preparation is fast and normally takes less than 15 min.
Recent Examples of Hydrogels
Using the JEOL JSM-7600 CryoSEM , we are able to achieve hydrogel structures and nanoparticle distributions in their hydrated state. The hydrogel was plunge frozen and transferred to Alto-2500 sample preparation chamber and sputter coated with 10 nm Au-Pd. The SEM images were taken at -150 °C.
This example is from fibrin-thrombin hydrogel with incorporated colloidal particles. The SEM sample was prepared by plunge freezing the hydrogel. After the hydrogel was transferred to Alto-2500, it was cryo-fractured and sublimated at -90 °C for 15 min to reveal the microstructure.