Tecnai spirit biotwin electron microscope

Large and small SPIO NWs (L-SPIO NWs and S-SPIO NWs, respectively) were synthesized from 15 to 25 kDa dextran, Fe(III) chloride, and Fe(II) chloride using a modified Molday precipitation method^{30 (link)} as described previously. ^{26 (link)} The ratio between dextran and iron salts determined the final size of the nanoparticles.^{26 (link)} Particles were resuspended in sterile phosphate-buffered saline (PBS), filtered through a 0.45 μm filter, and stored at 4 °C. Size and ζ potential were determined using a Zetasizer Nano ZS (Malvern Instruments Ltd., Malvern, UK). The intensity-weighted distribution was used to report the hydrodynamic diameter of nanoparticles and liposomes. For TEM analysis of S-SPIO NWs and L-SPIO NWs, the imaging of nonstained samples applied on carbon grid was performed using a FEI Tecnai Spirit BioTwin electron microscope at 100 keV. For TEM analysis of Feraheme, the imaging of nonstained particles was performed at Thermo Fisher Scientific (Americas Nanoport, Hillsboro, OR) using an FEI Apreo microscope. The imaging was performed in immersion mode with STEM 3+ detector and landing energy of 30 keV.

For each MMC, a bacterial suspension was prepared. 5 µl of
bacterial suspension was placed on a carbon-coated nickel grid. After 1 minute,
the sample was blotted off by touching the edge of the grid to filter paper.
Once the grid was dry, images were taken with a Tecnai Spirit BioTwin electron
microscope (FEI, Hillsboro, Oregon) operating at 120 kV, equipped with AMT
BioSprint29 digital camera.

TEM imaging was conducted to visualize the iron oxide core using an FEI Tecnai Spirit BioTwin electron microscope (Electron Microscopy Facility at the University of Colorado Boulder). Size and zeta potential measurements of nanoparticles were determined using a Zetasizer Nano ZS (Malvern Instruments). The intensity weighted size distribution peak value was used to report hydrodynamic diameters of nanowires. For some samples, the number weighted diameter was measured with a particle tracking analysis instrument NanoSight (Malvern Instruments). For simplicity, the absolute count of cells in each size bin (y axis) was converted to a percentage of cells. AFM was performed at the Nanomaterials Characterization Facility, University of Colorado Boulder. Highly diluted samples were dried on a cleaned borosilicate glass surface and imaged using a Nanosurf EasyScan 2 AFM (110 μm scan head) with an Aspire Conical AFM probe tip (CT170R) using intermittent contact (dynamic force mode) to avoid damage to the samples. FIB–SEM was used to visualize overall particle shape (including the shell) with an FEI Nova 600 Nanolab Dual Beam System equipped with a Schottky field emitter. Samples were dried on a piece of silicon substrate and coated with carbon to avoid charging. The stage was tiled to 52° during the observation and imaged at an accelerating voltage of 5 kV.