Who said "Money does not smell" ? Deconstructing the Euro Banknote Odor Profile: A Multimodal Chemical and Behavioral Approach

Abstract

Cash detection dogs (CDDs) are essential tools in forensic investigations, yet the specific volatile organic compounds (VOCs) that drive their responses to banknotes remain poorly understood. This study presents the first integrated chemical, behavioral, and predictive analysis of euro banknote odor profiles, combining thermal desorption–gas chromatography–mass spectrometry, controlled canine detection trials, and machine learning modeling. VOC profiles were characterized for six euro denominations, €10 notes printed in Austria and Germany, and for individual banknote components (paper, varnish, and 22 inks). Eight major VOCs were shared across denominations, but relative abundances varied significantly, enabling chemical discrimination by denomination, origin, and component. Behavioral assays with 22 operational CDDs revealed consistently high detection rates across all denominations and printing origins, with lower responses observed for €5 notes and certain individual components. Partial Least Squares Regression (PLSR) identified a restricted set of VOCs, spanning abundant and trace compounds, that best predicted canine responses. Notably, some low-abundance compounds elicited strong alerts, whereas several major ones had limited behavioral relevance, underscoring that olfactory salience is not solely abundance-driven. Findings highlight that CDD detection is shaped by a combination of key odorants, mixture effects, and possible generalization from prior exposure to chemically related scents. This work provides the first chemical–behavioral map of euro banknote odor signatures and demonstrates the potential of predictive modelling to refine canine training aids, with implications for forensic applications involving manufactured, multi-component odor sources.