I did research on drug delivery for my masters degree and it has been published. But in the end I knew that I had no interest in it at all. Actually my interest was computational drug design, which I couldn't find a professor specialized in that in my school. Now that I want to apply for a graduate school, I'd like to work in a computational field. Although I know a lot about it, I have no published experience. My question is: Is it a wise decision? I mean, having no published experience would lower my chances of getting admitted in that course, but on the other hand, if I chose drug delivery, I might have not much motives to improve due to the lack of interest.
I'd say, go for it! Two reasons:
1) If you stay in academia, you're going to use your creative and imaginative skills a lot. And my experience is that they don't work much if you aren't interested in what you're doing.
2) You will have an interesting edge over other candidates since you come from a close, but not overlapping area.
It will take determination to enter a new area, but I think you're absolutely on the right track in pursuing what you're passionate about; and yes, you're still in time! Don't give up. :)