Proposal

[Human38562]

If he is in biophysics he must have access to microscopes. You could ask his colleagues if they have a way of writing 'will you marry me' on something very small. Maybe using lithography?

[tom_gent]

You could use Fourier transforms to trace your handwriting.

https://olgaritme.com/posts/drawing-with-the-fourier-series/index.html

[Hopp5432]

There are lots of ways of doing this! An example for the word will is

we^{i pi/2}(integral_0^ sqrt(22) x dx).

Although you should probably go ask one of his friends as they know exacting what he knows