CLPEX Chat Board

Okay, folks, maybe somebody on here can answer this question that was posed to me by a newer member of the unit. We have always processed porous items using DFO followed by Ninhydrin because if you use Ninhydrin first, DFO won't fluoresce.

Why doesn't DFO fluoresce after Ninhydrin?

That's not the reasoning I am aware of. The reason to sequence DFO (or indanedione) before ninhydrin is because DFO and indanedione only react with some of the amino acids present in the fingerprint deposit, while ninhydrin reacts with all available amino acids in the deposit. So, if you were to use ninhydrin first, the theory would be that there are no more amino acids left for DFO or indanedione to attach to.

Thanks!

I think timbo is mostly correct.

According to H. Lee's 'Advances in FP Technology, 2nd Ed.' (I know there's a 3rd edition but I don't have it), ninhydrin mainly reacts with alpha-amino acids. But, like timbo said, if nin were used first, you wouldn't get the fluorescent results with DFO or Indanedione since there wouldn't be as much left over with which to react.

The actual mechanism is still relatively unknown.

In any event, research and personal experience shows that DFO and Ind print development is much better than Nin (because it's more sensitive and because it can resolve any background "noise" due to colored surfaces). There has only been one time that I was able to develop nin prints on paper that didn't develop first with DFO or Ind; hence, the sequential processing method!