Development of Latent Fingerprints via Aryldiazonium Tetrachloroaurate Salts on Copper Surfaces: An XPS Study

Surface studies of developed fingerprints have aided in the elimination of criminal cases before moving to the court. The combination of X-ray photoelectron spectroscopy (XPS) with the aryldiazonium gold­(III), 4-O₂NC₆H₄N₂⁺AuCl₄^–, surface modifier has been shown to be a novel approach in latent fingerprint detection and development for the quantification of film elements. The robust gold–aryl film was developed on the reducing chemicals excreted in the sebaceous fingerprints without the need for external stimuli and at a lesser extent after contacting the free metal surface. The concurrent reduction of the diazonium functional group and gold­(III) from [AuCl₄]^‑ developed a robust gold–aryl film, which showed increasing gold(0) quantity in the time range of 30–120 min over copper coins and model flat sheets. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) support the presence of reduced gold on the top of the latent fingerprints and the presence of CuO resulting from the reaction of the diazonium salt with copper metal. This research combines the quantification of deposits using XPS, a surface-sensitive technique for chemical analysis, in addition to surface imaging.