Enhancement imaging of developed latent blood fingerprints using TOF-SIMS

As one of the most common types of evidence in violent cases, blood fingerprints play an important role in identifying suspects. Typically, Latent blood fingerprints from a crime scene require the application of chemical development reagents followed by photographing to visualize the ridge detail. However, conventional development techniques are not effective in the visualization of poor latent blood fingerprints due to the formation conditions. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is a surface analysis technique that combines high mass resolution and high spatial resolution to recover through mass spectrometry imaging (MSI) to reveal fingerprints that are invisible to the naked eye, especially conventional visualization methods. In this study, an enhancement method for latent blood fingerprints was established by analyzing blood fingerprints that showed poor visibility using conventional methods (acid yellow, amido black 10B, tetramethylbenzidine) on plastic sheets, aluminum foil, various papers, and other objects. Additionally, blood samples were diluted with distilled water at concentration gradients of 1:5, 1:10, 1:20, and 1:100 to test the method's sensitivity. Latent fingerprints of blood that aged 14, 30, and 54 days were also examined. Results showed that this method not only enhances the development of fingerprints under challenging conditions but also allows for the recovery of incomplete fingerprints and the separation of overlapping fingerprints. Compared to conventional methods, this approach significantly improves the development effect of latent blood fingerprints while maintaining universality, reliability and practicality.