Hello to all.
My peers and I intend on using micro-CT scans to generate images of the penises of small mammals; in particular, we would like to assess the shape of the baculum (penis bone), glans and shaft of the penis. Although the process seems in general to be relatively straightfoward, part of our sample has gone through sweeping electronic microscopy (SEM) and is thus covered by a thin layer of metal, which can be platinum or gold, depending on the specimen.
My question is, is anyone familiar with any protocol for removing such metal layers from biological samples? Since we already have images of the soft tissue of the samples that went through SEM, we are willing to risk some damage to the soft-tissue layers of the biological sample; however, we need the baculum to remain intact within each penis.
P.S.: It has been pointed out by some colleagues that some acids may be able to remove the gold/platinum, but we are afraid that these will also damage the bone inside the penis to a greater extent than we are willing to risk.
There are a few potential non-destructive methods for removing metal coatings from biological samples for electron microscopy:
- This uses ionized gas (usually argon or oxygen) to gently sputter away surface contaminants. It can remove metal coatings while minimizing damage to delicate samples. The plasma power and duration need to be optimized to remove the coating but not etch the underlying sample.
- Some chemical etchants like iodine or cyanide solutions can preferentially dissolve metal coatings faster than biological tissues. This may work for your purposes if the etch rate of the coating is much faster than the bone. Proper concentrations and etch times would need to be tested.
- Applying a voltage in an electrolyte bath can cause the metal coating to oxidize and dissolve from the surface. Again, the voltage and solution composition can be tuned to selectively and gradually remove the coating.
- Very gentle mechanical polishing with fine abrasives could potentially remove surface metal layers while keeping the overall structure intact. Though this runs a higher risk of damaging the sample.
The key for all these methods is controlling the rate and degree of metal removal to avoid over-etching the valuable biological structures underneath. I'd recommend starting with low concentrations and gentle plasma or chemical etching first. The goal is removing the minimum amount of coating required for analysis, without compromising the integrity of the soft tissues or bone
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