Suppose you improved an old method with a novel technique. Is it OK to say that it (your technique) is your trump card in paper? If not, what is your suggestion?
The metaphorical use of 'trump card' means that you used a sneaky technique to overcome an obstacle (and win against a stronger opponent). If you are improving an old technique, then your use of the metaphor would come across as very arrogant, that you were in competition with the authors of the prior technique and that you beat them. Not only would the prior authors resent such an implication, other readers would sense this arrogance and look on unfavorably to your intentions.
If you need a metaphor that shows that you are improving on a prior result (by extending it), then do not use 'trump card'.
I guess you can use the term in science papers.
If you have improved an old method with a novel technique and if that gives you an edge over others, then it sure is your trump card. Trump card means any resource that can be used at an opportune moment.