Surface-assisted laser desorption/ionization imaging mass spectrometry: noble metal nanoparticles as efficient substrates for forensic applications

Abstract

Chemical analysis of forensic evidence collected from a crime scene is important for criminal investigations. The uniqueness and specificity of chemical information obtained from the forensic sample is critical for successful prosecution. Imaging Mass Spectrometry (IMS) is a powerful analytical technique which allows direct chemical analysis of forensic samples without extensive sample extraction. With high sensitivity and specificity, the chemical identity and the spatial distributions of analytes in the sample will be revealed. Recently nanomaterials have been used in Surface-Assisted Laser Desorption/Ionization (SALDI)-based MS and IMS as substrate for forensic sample analysis. We have applied Gold Nanoparticles (AuNPs) as efficient LDI substrate in previous studies. Forensic samples including latent fingerprint and questioned documents were firstly coated with a layer of AuNPs using solvent-free Argon lon Sputtering, followed by the subsequent spectrometric analysis. Double imaging of latent fingerprint can be developed. The latent fingerprint can be optically visualized due to the plasmonic properties of AuNPs. Exo- and endogenous compounds found on latent fingerprint can also be molecularly imaged by SALDI-IMS. Questioned document such as cheque with suspicious altered writing can be examined through the minimally-destructive ink analysis by SALDI-IMS. Writings using different pens can be distinguished by the MS images targeting different characteristic ions with specific m/z values. Hence, altered words can be identified on the questioned cheque. Our team is developing other noble metal nanoparticles, such as silver nanoparticles (AgNPs), platinum nanoparticles (PtNPs), palladium nanoparticles (PdNPs) and bimetallic nanoparticles with well-defined physiochemical properties as potential efficient substrates for SALDI-MS and -lMS analysis. We anticipated that the use of nanoparticles as substrate will enhance the analytical performance and extend the application in forensic science.