Teaching Old Presumptive Tests New Digital Tricks with Computer Vision for Forensic Applications

17 April 2023, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Presumptive (or 'spot') tests have served forensic scientists, law enforcement, and legal practitioners for over a hundred years. Yet, the intended design of such tests, enabling quick identification of drugs by-eye, also hides their full potential. Here, we report the development and application of time-resolved imaging methods of reactions attending spot tests for amphetamines, barbiturates, and benzodiazepines. Analysis of the reaction videos helps distinguish drugs within the same structural class that, by-eye, are judged to give the same qualitative spot test result. It is envisaged that application of these results will bridge the existing suite of field and lab-based confirmatory forensic tests, and support a broader range of colorimetric sensing technologies.

Keywords

computer vision
spot test
presumptive test
imaging
amphetamine
barbiturate
benzodiazepine

Supplementary materials

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