An update on biological arrays in forensic toxicology: a review

Background. The search for alternative biological matrices in toxicological analyses is decisive in the most critical cases. Alternative samples to blood and urine are useful both when these are not available and in providing additional information regarding drug exposure and analytical benefits. The goal of our research is to present an updated review on the most recent literature regarding the application of common alternative matrices in forensic toxicology, highlighting the strengths and weaknesses of each of them. Methods. A review of the most recent scientific evidence in the literature was performed on most biological fluids and matrices, looking for the best field of application in forensic toxicology for each in the search for both traditional drugs and new psychoactive substances (NPS). Results. This paper discusses the characteristics of eight biological matrices used in forensic analysis (oral fluid, hair, nails, sweat, humour vitreous, meconium, breast milk and biological tissue) as alternatives to traditional whole blood and urine samples. Each matrix presents advantages related to sampling, extraction, detection windows, and typical drug levels, among other aspects. However, these matrices also face limitations such as restricted drug incorporation (based on their physical-chemical properties), difficulty correlating concentrations with effects, low xenobiotic levels, and the requirement for more sensitive analysis techniques. While data on detecting traditional drugs of abuse (e.g., cocaine and amphetamines) in alternative matrices is extensively available, information on searching emerging drugs like NPS in these matrices are still under study today. Conclusions. Knowing the potential of each known biological matrix is of paramount importance to the forensic toxicologist and forensic scientist. The study of alternative matrices to blood and urine has increased in recent years, especially given the advantage that some of these matrices offer and the possibility to be used when blood or urine are unavailable. However experts in the field must be familiar with the properties and limitations of the different matrices used and should be able to correlate the result obtained with the type of substrate used. The use of alternative matrices is becoming increasingly central in forensic toxicology, especially in the search for past substance abuse. There is a need to further investigate how NPS can be searched in the different matrices.