Research On Detection Of Exogenous Fingerprint Substances Using TOF-SIMS

Fingerprints play an important role in the criminal investigation as one crucial type of physical evidence for personal identification in the field of forensic science.In recent years,with the development of analytical techniques,the abundant chemical information in fingerprints is increasingly exploited in addition to the traditional way of acquiring morphological information,which has greatly enhanced the evidence value of fingerprints.Time-of-flight secondary ion mass spectrometry(TOF-SIMS),as one of the mass spectrometry imaging technologies,possesses high spatial resolution and mass resolution,which can realize in-situ analysis of multiple substances in fingerprints without destroying the ridges,and simultaneously obtain the distribution images of ions originating from fingerprints.Therefore,in this paper,the TOF-SIMS was used to study the detection of exogenous fingerprint substances from the following three parts.In the first part,TOF-SIMS was used to detect the fingerprints contaminated by 3 common skin care products(hand cream,moisturizer,suncream).By comparatively analyzing the mass spectrum signals of fingerprints stained with skin care products and natural fingerprints on various types of substrates,the humectant ingredients in hand cream and moisturizer as well as the unique sun-proof ingredients in sunscreen were detected,and fingerprints stained with skin care products could be differentiated from natural fingerprints based on the ion images of fingerprints substances.Moreover,the fragment ion signals of fingerprint substances were utilized combined with principal component analysis,which effectively distinguished hand cream components from endogenous secreted substances in fingerprints.In the second part,TOF-SIMS was used to detect the fingerprints contaminated by 4hypnotic and sedative drugs(barbiturate,phenobarbital,alprazolam,triazolam).By analyzing the mass spectrum signals and ion distribution of fingerprints on various types of substrates,the molecular ions or quasi-molecular ions corresponding to 4 hypnotic and sedative drugs were detected respectively,and fragment ions of a six-membered ring structure shared in barbiturates were also detected,which could further distinguish barbiturates from other substances.In addition,it was found that the effect of the porous surface on the testing results was mainly related to the permeability of the tested substances.In the third part,the blood in fingerprints was detected using TOF-SIMS to explore the problem of discriminating between genuine and faux blood fingermarks.Based on the comparison of the intensity and distribution of the characteristic ions in the area of fingerprint ridges and furrows,four deposition mechanisms of blood fingermarks were distinguished from the two dimensions of both mass spectrum and images,and the essential differences of different blood fingerprint models were obtained.Additionally,in order to strengthen the practical application connection,the blood fingermarks treated with tetra-methylbenzidine reagents were also distinguished,and the fragment ions of the reaction products of tetra-methylbenzidine and blood were detected.In this paper,the feasibility and applicability of TOF-SIMS technique for testing exogenous fingerprint substances was verified via the detection of skin care products as well as hypnotic and sedative drugs in fingerprints.Meanwhile,a model for distinguishing the exogenous contaminations from endogenous secretions in fingerprints was established by combining multivariate statistical analysis,which provided new ideas for the utilization of TOF-SIMS signals in detecting exogenous fingerprint substances.Finally,from the practical perspective,the challenging problem of discriminating the genuine or faux blood fingermarks was solved by detecting the blood in fingerprints.