DETECHIP has been used in testing analytes including caffeine, cocaine, and tetrahydrocannabinol (THC) from marijuana, as well as date rape and club drugs such as flunitrazepam, gamma-hydroxybutyric acid (GHB), and methamphetamine. This study investigates the intermolecular interaction between DETECHIP sensor eosin Y (DC1) and the analyte (caffeine) that is responsible for the fluorescence and color changes observed in the actual array. Using 1H-NMR, 1H-COSY, and 1H-DOSY NMR methods, a proton exchange from C-8 of caffeine to eosin Y is proposed. 1. Introduction DETECHIP, a highly selective and sensitive molecular sensor that produces color and fluorescence changes in the presence of analytes, was recently developed. A quick, sensitive, and selective detection system is required for many applications, such as alerting security officers to the presence of explosives or their precursors, preincident monitoring/screening for homeland security purposes [1] such as weapons of mass destruction, and detection and quantification of doping compounds in competitive sports [2–5]. The method that is currently most widely used for the detection of such substances is gas chromatography-mass spectrometry (GC-MS) [6, 7]. However this method requires a skilled operator and cannot be easily miniaturized. Current screening reagents for abused narcotics like flunitrazepam (often used for date rape, assault, or theft) [8], methylephedrine, caffeine, nicotine, and others include immunoassays [9], ion trap mobility spectrometry [9–11], wet colorimetric assays [12–14], spot tests such as Marquis [13], Scott Drug Testing Company drug tests (http://www.scottcompany.com), or the b-Glucuronidase Drug Analysis Bundle (Sigma-Aldrich) and Magnotech technology testing [15]. DETECHIP uses an array of sensors that can be used for identification of drugs and other molecules by fluorescence and color changes [16–18]. This method relies on molecular interactions between the analyte molecules and the DETECHIP sensors [18]. Unlike other color tests which provide a single “yes” or “no” response, DETECHIP gives multiple simultaneous responses in the form of color and fluorescent changes using two different buffers, allowing users to quickly characterize suspect materials. Figure 1 shows an example of a 96-well plate DETECHIP assay. Eight sensors (DC1–DC8) are added to the rows in the plate in two different buffers (A + B), and the analytes are tested alongside a control in the columns of the plate. Figure 1: Setup of a typical DETECHIP assay showing presence or absence of color changes of the
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