Q: Should there be a single style of voice in the Methods section?

You should be wary of “blanket” recommendations, such as ‘Always use the active voice’ and ‘Never type any word entirely in capital letters.’ Writing is too nuanced for such recommendations to be effective. The important consideration is what is important and what the reader needs to know.

For many of the actions described in the Methods section, the action (what was done) is more important than the doer (who did it). For example, in the sentence ‘Lipids were extracted in a mixture of chloroform and methanol (2:1, v/v)’, does it matter who did the extraction? Mentioning the doer in this case adds no useful information. On the other hand, examining a specimen through a microscope for identifying the species calls for experience, judgment, and knowledge. Therefore, ‘We identified the fungus as Curvularia lunata by examining the fungal spores’ is more informative than ‘The fungus was identified as Curvularia lunata,’ because it is important to know who made the identification.

Having said that, you should also be careful of ignoring your supervisor’s suggestions. Perhaps you could be diplomatic and use the active voice at least a few times in the Methods section. :-)

For more help on the various points discussed here, you may refer to the following resources:

• How to effectively use active and passive voice in research writing
• Supply adequate details of items mentioned in the materials and methods section
• How to draft a strong methods section that showcases your work [Handbook]

Hope that helps. All the best for your manuscript!