In case helpful, this is from the FAQ document (linked on the OP page):
Writing sample: What is the intended purpose of the writing sample? Does it need to be related to AI or biotechnology? Are there other requirements?
The writing sample is primarily intended to display your ability to write clearly for non-specialist audiences such as policymakers. It is not necessary that the sample be related to AI, biotechnology, or another technology topic. The writing sample can be either published or unpublished work, either analytical or expository in genre, and does not necessarily require any particular type of citation or sourcing. We strongly prefer a single-authored piece, but feel free to submit whatever you think best represents your personal abilities (e.g. if you contributed almost all the writing, and a co-author contributed data analysis, that would be fine). Please do not write something new for the application; you may use older pieces (graduate school or college essays) if needed.
In case helpful, this is from the FAQ document (linked on the OP page):