MnCo2O4 spinel nanoparticles as a dusting powder for sebaceous and natural latent fingermarks on substrates of different porosities

Dark particulate developers remain the most widely applied means of visualizing latent fingermarks. Manganese cobalt oxide (MnCo 2 O 4 ) nanoparticles were prepared by alkaline coprecipitation at 80 °C and characterized by XRD, FTIR, FESEM, and EDS, which indicated the formation of the cubic spinel phase of MnCo2O4 with a crystallite size of approximately 21 nm, a particle size of approximately 50 nm, and particle aggregation. Sebaceous and natural fingermarks on ten substrates were developed by powder dusting, visually graded, and scored using NIST Fingerprint Image Quality 2 (NFIQ 2). Sebaceous marks received grades of 4 or 5 on eight substrates, whereas natural marks achieved these grades on five substrates. NFIQ 2 scores correlated with visual grades (Spearman ρ = 0.69) and were higher for sebaceous marks (median 33.5 versus 15.0). Substrate texture inflated the automated minutiae counts, and microscopy showed particle deposition largely confined to the ridges.