Kiran, CSPD and CDP have differing modes of application. You can try the following and see if it helps -

1. Spread the diluted CDP-Star on a clean, grease-free glass plate sufficient to cover the area reqd by your blot.

2. Keep a Saran Wrap beside the glass plate.

3. Put the DNA side of the blot on it. (Just touch it. Do not keep it there. You may use a small cylindrical vial or glass pipette to roll over the blot just in case you have bubbles.)

4. Immediately transfer your blot to the Saran Wrap (DNA Side Up). Fold the Saran Wrap over it. (Avoid bubbles).

5. Keep a stack of at least 2-3 Xray films on it.

6. Expose for 1-2 mins. If your probe has bound, you are sure to get a clean signal.

See if it helps.

Rohit, thank you very much for your reply. I have one doubt that can we use GE's CDP-star for ROCHE anti- DIG anti body Fab Fragments?

I cannot figure out of a reason as to why you should not be able to. Because the CDP-Star is just a substrate, and the Roche anti-DIG-Fab fragments have the AP conjugated to it. Its just that the enzyme should cleave the substrate. However, you may check the solvent pH and/or composition of the GE-CDP-Star, because Roche Fab AP functions best at pH 9.5, which, as you may be knowing, is maintained by Tris in the solution of NaCl. Check the compatibility.

Best of luck !!

Thanks Rohit,

I am going to try it another time.