The finding that drugs and metabolites can be detected from fingerprints is of potential relevance to forensic science and as well as toxicology and clinical testing. However, discriminating between dermal contact and ingestion of drugs has never been verified experimentally. The inability to interpret the result of finding a drug or metabolite in a fingerprint has prevented widespread adoption of fingerprints in drug testing and limits the probative value of detecting drugs in fingermarks. A commonly held belief is that the detection of metabolites of drugs of abuse in fingerprints can be used to confirm a drug has been ingested. However, we show here that cocaine and its primary metabolite, benzoylecgonine, can be detected in fingerprints of non-drug users after contact with cocaine. Additionally, cocaine was found to persist above environmental levels for up to 48 hours after contact. Therefore the detection of cocaine and benzoylecgonine (BZE) in fingermarks can be forensically significant, but do not demonstrate that a person has ingested the substance. In contrast, the data here shows that a drug test from a fingerprint (where hands can be washed prior to donating a sample) CAN distinguish between contact and ingestion of cocaine. If hands were washed prior to giving a fingerprint, BZE was detected only after the administration of cocaine. Therefore BZE can be used to distinguish cocaine contact from cocaine ingestion, provided donors wash their hands prior to sampling. A test based on the detection of BZE in at least one of two donated fingerprint samples has accuracy 95%, sensitivity 90% and specificity of 100% (n = 86).
This thesis explores the feasibility of testing for drugs from a fingerprint. Previous publications have reported drug detection in fingerprints from either drug users or after contact with a substance. There are possibilities to exploit these findings either for forensics (where a finger-mark is deposited at a crime scene to give intelligence about a donor) or for drug testing (where fingerprints are deposited under controlled conditions). In forensic science, it may be sufficient to know that a drug has been either handled or ingested within a specific time frame. In contrast, for drug testing, it may be necessary to exclude handling of drugs as a possible source. In either case, it is necessary to understand the significance of detecting a drug or its metabolite in a fingerprint.
This thesis explored the significance of detecting a selection of illicit drugs in fingerprints. In Chapter 4 and Chapter 5, a rapid analysis method based on paper spray high resolution mass spectrometry is developed and validated for cocaine and its metabolite, benzoylecgonine (BZE), and the method is applied to the fingerprints of non-drug users and drug users respectively. As a result, cocaine and BZE were found in samples from both non-drug users (set as environmental cut-off) and drug users. The detection rate from drug users was above 90 % and there were no false positive using this method. Moreover, handwashing involvement became indicative of either ingestion of cocaine OR recent contact with cocaine. In Chapter 6 and 7, imaging mass spectrometry techniques were employed to determine whether contact and ingestion scenarios can be distinguished via spatial distribution of analytes. Those results supported the hypothesis that hot spots would be formed in fingerprints after contact whereas analytes would be evenly distributed in fingerprints after ingestion. The presence of BZE was also used to in distinguishing fingerprint samples from the two scenarios. In Chapter 8 and 9, the paper spray mass spectrometry methodology was expanded to a selection of novel psychoactive substances (NPS) relevant to a prison environment using fingerprints for the first time. The method was applied to the fingerprints of prisoners before and after participants washed their hands. As a result, NPS substances were not detected from any participants, in agreement with their urine testing. Finally, in Chapter 10, the data collected in Chapter 4 and 5 was analysed retrospectively for detection of heroin and 6-AM in fingerprints to explore the possibility of carrying out an untargeted analysis. The sensitivity of the method was not as good as for cocaine and benzoylecgonine (BZE), which led to the lower detection rate of heroin and 6-AM than that of cocaine and BZE. However, this study proved that the paper spray method could still provide qualitative and quantitative results of heroin detection in fingerprints.
This study demonstrates that in the future with a suitable, deployable high resolution mass spectrometer, paper spray mass spectrometry could be used to detect cocaine, its metabolites and NPS for evidential purposes within the confines of a police station.