2D and 3D structure of ssDNA

Question

[Samane]

I need a software or any online database that could help me about 3d and 2d structure of little sequence ( 30 bp)...I found some software but they need pdb format that I don't know hoe to use it because my sequence is not a protein sequence it is a aptamer sequence that we choose it to detect a microorganism....

for 2d Structure I used Unafold tools but I have a little problem about their ionic condition too?

I would highly appreciate if you could please lend your valuable suggestions/advice to me.

thanks a lot to all of you.