This publication presents one of the first uses of silicon oxide nanoparticles to detect fingermarks. The study is not confined to showing successful detection of fingermarks, but is focused on understanding the mechanisms involved in the fingermark detection process. To gain such an understanding, various chemical groups are grafted onto the nanoparticle surface, and parameters such as the pH of the solutions or zeta potential are varied to study their influence on the detection. An electrostatic interaction has been the generally accepted hypothesis of interaction between nanoparticles and fingermarks, but the results of this research challenge that hypothesis, showing that the interaction is chemically driven. Carboxyl groups grafted onto the nanoparticle surfaces react with amine groups of the fingermark secretion. This formation of amide linkage between carboxyl and amine groups has further been favoured by catalyzing the reaction with a compound of diimide type. The research strategy adopted here ought to be applicable to all detection techniques using nanoparticles. For most of them the nature of the interaction remains poorly understood.