title: Make caffeine visible: a fluorescent caffeine "traffic light" detector.
abstract: Caffeine has attracted abundant attention due to its extensive existence in beverages and medicines. However, to detect it sensitively and conveniently remains a challenge, especially in resource-limited regions. Here we report a novel aqueous phase fluorescent caffeine sensor named Caffeine Orange which exhibits 250-fold fluorescence enhancement upon caffeine activation and high selectivity. Nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy indicate that π-stacking and hydrogen-bonding contribute to their interactions while dynamic light scattering and transmission electron microscopy experiments demonstrate the change of Caffeine Orange ambient environment induces its fluorescence emission. To utilize this probe in real life, we developed a non-toxic caffeine detection kit and tested it for caffeine quantification in various beverages. Naked-eye sensing of various caffeine concentrations was possible based on color changes upon irradiation with a laser pointer. Lastly, we performed the whole system on a microfluidic device to make caffeine detection quick, sensitive and automated.
authors.affiliation: Department of Chemistry & MedChem Program of Life Sciences Institute, National University of Singapore, 117543 Singapore.
authors.forename: Wang
authors.initials: W
authors.lastname: Xu
authors.forename: Tae-Hyeong
authors.initials: TH
authors.lastname: Kim
authors.forename: Duanting
authors.initials: D
authors.lastname: Zhai
authors.forename: Jun Cheng
authors.initials: JC
authors.lastname: Er
authors.forename: Liyun
authors.initials: L
authors.lastname: Zhang
authors.forename: Anup Atul
authors.initials: AA
authors.lastname: Kale
authors.forename: Bikram Keshari
authors.initials: BK
authors.lastname: Agrawalla
authors.forename: Yoon-Kyoung
authors.initials: YK
authors.lastname: Cho
authors.forename: Young-Tae
authors.initials: YT
authors.lastname: Chang
mesh_terms: D015374:Biosensing Techniques; D002110:Caffeine / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry*; D046210:Microfluidic Analytical Techniques; D019906:Nuclear Magnetic Resonance, Biomolecular; D012680:Sensitivity and Specificity; D017550:Spectroscopy, Fourier Transform Infrared; D014867:Water / Q000737:chemistry
chemical_list: D005456:Fluorescent Dyes; D014867:Water; D002110:Caffeine