Contents lists available at ScienceDirect Talanta journal homepage: www.elsevier.com/locate/talanta Screening for cocaine on Euro banknotes by a highly sensitive enzyme immunoassay Nahla A. Abdelshafi a,b , Ulrich Panne a,b , Rudolf J. Schneider a,c, ⁎ a Bundesanstalt für Materialforschung und -prüfung (BAM), 12205 Berlin, Germany b School of Analytical Sciences Adlershof (SALSA), Humboldt-Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germany c Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany ARTICLE INFO Keywords: Cocaine Euro banknotes Drugs on bills Enzyme-Linked Immunosorbent Assay ELISA ABSTRACT This study focused on quantitative detection of cocaine on Euro banknotes in Germany. A sensitive direct competitive immunoassay was developed and optimized with a limit of detection (LOD) of 5.6 ng/L. Exhaustive cocaine extraction by solvent was tested using different methanol concentrations and buffered solutions. Cross- reactivity studies were performed to determine the degree of interference of cocaine metabolites with the immunoassay. Sixty-five Euro banknotes obtained from different districts in Berlin were evaluated. A 100% contamination frequency with cocaine was detected. A comparison between the amount of cocaine extracted by cotton swabbing of one square centimeter of the banknote showed a good correlation for lower contamination levels. This assay showed high sensitivity of detecting pg of cocaine per 1 cm 2 of one banknote by swabbing 1 cm 2 : 0, 14, and 21 pg/cm 2 . Moreover, three notes of different denominations revealed high cocaine concentration; 1.1 mg/note, and twice 55 μg/note. 1. Introduction Cocaine consumption continues to grow globally. An estimated 21 million people were reported to be consumers of cocaine in 2012 [1]. Usage in Western countries remains the highest. In North and South America cocaine consumption levels increased by 1.8% and 1.2%, respectively, while the percentage dropped by 0.3% in Central and Western Europe [1]. Banknotes can be contaminated by numerous drugs: cocaine, methamphetamine, heroin, morphine, codeine, and others [2,3]. Cocaine contaminates nearly all types of banknotes including US dollars, UK pounds, and Euros [4], where the contamination frequen- cies reached 100% with UK and US banknotes. An average of 155 [4], 19.9 [5]. and 28.75 [4] μg/note was detected on Spanish, British and American banknotes, respectively. One source of contamination can be through direct contact, a massive amount of cash being involved in drug trafficking with the same people handling the cocaine powder and the money. Another source of direct contamination is rolling up the banknote for sniffing the powder through the tube formed. Yet, there are also indirect pathways. Indirect contamination occurs by the contact of “clean” banknotes with the cocaine-contaminated ones in automated teller machines (ATM) and cash counting machines and has been considered a major source of contamination [6–8]. In the attempt to detect cocaine on banknotes, several analytical techniques have been employed. Chromatographic methods rank as the most common ones since coupling with mass spectroscopy provide the high sensitivity required [4]. For example, GC-MS reached a LOD for cocaine of 1 ng/mL [2], and the sensitivity increased with MS/MS coupling and positive-ion chemical ionization mass spectrometry producing LODs of 0.15 ng/ note [9] and 1 ng/note [10], respectively. Liquid chromatography (LC) coupled with MS/MS indicated higher sensitivity than GC-MS/MS with a detection limit of pg per Euro banknotes as reported by Bones et al. [3]. Other analytical techniques like spectrofluorometry [11], electro- chemiluminescence sensor [12], aptamer-based electrochemilumines- cence biosensor [13], capillary electrophoresis (CE) with electroche- miluminescence (ECL) detection [14], CE with UV detection [15], and thermal desorption tandem mass spectrometry were also used for cocaine determination on banknotes [16]. Extraction of cocaine from bank notes has been carried out by different methods such as direct thermal desorption, vacuum systems, and solvent extraction [4]. Solvent extraction can be an effective method with reduced damage of the banknotes. The used solvents in http://dx.doi.org/10.1016/j.talanta.2017.01.004 Received 8 November 2016; Received in revised form 30 December 2016; Accepted 3 January 2017 ⁎ Correspondence to: Bundesanstalt für Materialforschung und -prüfung (BAM), Department of Analytical Chemistry; Reference Materials, Richard-Willstätter-Str. 11, D-12489 Berlin, Germany. E-mail address: rudolf.schneider@bam.de (R.J. Schneider). Talanta 165 (2017) 619–624 Available online 04 January 2017 0039-9140/ © 2017 Elsevier B.V. All rights reserved. MARK