Evaluation of DFO/PVP and its application to latent fingermarks development on thermal paper

A new method for improved development of latent fingermarks on thermal paper by 1,8-diazafluoren-9-one (DFO) treatment is described. Compared with conventional DFO solution, the mixed solution of DFO/PVP (polyvinylpyrrolidone) described here reduces black background staining without removing the thermosensitive layer and develops fingermarks by the reaction of DFO with amino acid deposited on the thermal paper's surface. An advantage of this approach is that the developed fluorescent fingermarks have high contrast and can be observed and photographed when excited in the 515 nm region and observed through an orange-red barrier long-pass filter with no background coloration. In addition, the method reported here does not involve any pre- or post treatment of the substrate and exhibits high sensitivity with good stability. Experimental results showed that the method was able to develop very old fingermarks, up to 154 days old, demonstrating the feasibility of using the method to develop identifiable latent fingermarks operationally. Furthermore, we extended our experiments to various types of thermal papers. Notably, this method exhibits several very attractive features, namely time saving, simple procedures, inexpensive, convenient operation, and PVP is non-toxic and reasonably priced. Finally, in this study an attempt has been made to explain the reaction mechanism of the process and the effects of PVP.