Magnetic carbon nanoparticles derived from candle soot for SALDI MS analyses of drugs and heavy metals in latent fingermarks

For decades, the analysis of fingerprints (FP) has been used as the primary biometric mean of human identification. In parallel, the chemical analysis of latent fingermark (LFM) with particular reference to “touch chemistry”, offers additional intelligence to forensic examination; as such, continuous improvements in the versatility and sensitivity of detection of the molecular make up of FM is of obvious importance. In this light, we propose a facile approach to synthesize magnetic carbon nanoparticles (MCNPs) from candle soot for extraction and detection of endogenous and exogenous FM components. Initially, endogenous components of FM including fatty acids (FAs), squalene and triacylgycerols (TAGs), were successfully extracted and detected using the developed MCNPs and surface assisted laser desorption/ionization-mass spectrometry (SALDI-MS). Furthermore, the MCNPs enabled the detection of exogenous substances including antihistamine, β-blocker, antibiotic drugs and lead in contaminated FMs, whilst providing characteristic and unique fragmentation patterns for each drugs in the FM. The influence of environmental factors such as temperature on the stability of the exogenous substances in FM was investigated by exposing the contaminated FM to different temperatures over 24 h, the findings revealed the drugs' instability at high temperatures and undergo different degrees of degradation whereas lead was more resilient to thermal stress. The detection of triprolidine, metoprolol and sulfamethoxazole from pharmaceutical tablets in FM was successfully achieved by gently touching the tablet powder. The limit of detection (LOD) values of the drugs in the tablet forms were 50, 200 and 750 ng mL−1 for triprolidine, metoprolol and sulfamethoxazole, respectively and their recovery rates were 91.17% for triprolidine, 94.67% for metoprolol and 120.86% for sulfamethoxazole. Finally, to create a genuine casework scenario, contaminated FM was deposited on glass and metal surfaces then subjected to extraction using MCNPs and magnet without compromising the FM impression. Substrate control experiments revealed that the glass surface exhibiting some background signal, however, they did not interfere with the analysis and satisfactory extraction efficiency of endogenous and exogenous components of the FM on both surfaces was obtained using the MCNPs. Overall, this study proves the capability of MCNPs as new SALDI-MS substrate for both extraction and detection of FM components gathering more information pertaining to the donor's lifestyle.