Teaching old presumptive tests new digital tricks with computer vision for forensic applications

Area of Science:

• Forensic Chemistry
• Analytical Chemistry
• Chemical Sensing

Background:

• Presumptive (spot) tests are traditional tools for preliminary drug identification in forensic science.
• The visual interpretation of spot tests can limit their discriminatory power, especially for structurally similar compounds.
• Existing methods often require laboratory confirmation, which can be time-consuming.

Purpose of the Study:

• To develop and apply time-resolved imaging for analyzing spot test reactions.
• To enhance the ability to differentiate drugs within the same structural class using spot tests.
• To explore the potential of advanced imaging to bridge field and laboratory forensic testing.

Main Methods:

• Development of time-resolved imaging techniques to capture reaction dynamics.
• Application of these methods to spot tests for amphetamines, barbiturates, and benzodiazepines.
• Analysis of video data to identify distinguishing features in reaction kinetics and visual changes.

Main Results:

• Time-resolved imaging successfully distinguished between drugs that appear identical by-eye using standard spot tests.
• Subtle differences in reaction kinetics and color development were identified as key discriminators.
• The method demonstrated potential for differentiating compounds within the same chemical class.

Conclusions:

• Time-resolved imaging significantly enhances the analytical capabilities of traditional spot tests.
• This approach offers a more nuanced and objective method for preliminary drug identification.
• The findings suggest broader applications in colorimetric sensing and forensic science.