No luck with postdoc hunting after PhD. Will things change with a major paper out?
Think about it this way: What would make things different after your paper is out?


You'd be a person who has published a paper in a prestigious venue.
More people will read about your work (in that paper and through it, elsewhere)


No. 1 will likely help to some extent - perhaps even enough to secure a post-doctoral position. But I think the key is no. 2; and publishing a paper is just one way to get people to know about your work and its importance. If you have a clear idea of what you want to be doing, you don't just "submit applications". You talk to relevant researchers in groups which could use your expertise and input, and make a pitch - for a collaboration, for a visit, and possibly for employment. The fact that you made 20 applications makes me guess that for most of them were somewhat generic: You noticed a posting and mailed/email your application. Try to find a researcher who would not pick you among applicants, but rather just offer you work because s/he believes you would help their lab and their research. 

Sorry for being a bit vague - I'm from a different academic field; but I think my point is valid for life scientists as well.