Visualising substrate–fingermark interactions: Solid-state NMR spectroscopy of amino acid reagent development on cellulose substrates

• Cross-polarisation 13C-MAS-NMR was used to study fingermark enhancement reagents.
• Ind–Zn, ninhydrin, DFO and isatin interact differently with cellulose.
• Three copy papers could be differentiated by NMR, FTIR and morphology.
• Chemical and physical attributes of cellulose in paper affect fingermark quality.
• 13C-MAS-NMR is a promising technique for studying fingermark enhancement reagents.

Most spectroscopic studies of the reaction products formed by ninhydrin, 1,2-indanedione–zinc (Ind–Zn) and 1,8-diazafluoren-9-one (DFO) when reacted with amino acids or latent fingermarks on paper substrates are focused on visible absorption or luminescence spectroscopy. In addition, structural elucidation studies are typically limited to solution-based mass spectrometry or liquid nuclear magnetic resonance (NMR) spectroscopy, which does not provide an accurate representation of the fingermark development process on common paper substrates. The research presented in this article demonstrates that solid-state carbon-13 magic angle spinning NMR (13C-MAS-NMR) is a technique that can not only be utilised for structural studies of fingermark enhancement reagents, but is a promising technique for characterising the effect of paper chemistry on fingermark deposition and enhancement. The latter opens up a research area that has been under-explored to date but has the potential to improve our understanding of how fingermark secretions and enhancement reagents interact with paper substrates.

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