Visual detection of Al 3þ ions using conjugated copolymer-ATP supramolecular complex Meng-Che Tu a, b, 1 , Deepa Rajwar a, b, 1 , Gopal Ammanath a, b, c , Palaniappan Alagappan a, b , Umit Hakan Yildiz d, e, ** , Bo Liedberg a, b, c, * a Center for Biomimetic Sensor Science, Nanyang Technological University, Singapore 637553, Singapore b School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore c Nanyang Institute of Technology in Health and Medicine, Interdisciplinary Graduate School, Nanyang Technological University, Singapore 637553, Singapore d Department of Chemistry, Izmir Institute of Technology, Izmir, Turkey e Stanford University School of Medicine, Palo Alto, CA 94304, United States highlights graphical abstract  A novel water soluble polythiophene copolymer that demonstrates colori- metric response for Al 3þ is proposed.  Optimized ratio of two poly- thiophene monomers is utilized for selective detection of Al 3þ .  Naked eye detection of Al 3þ is demonstrated without involving so- phisticated instrumentation.  Lowest concentration of Al 3þ for naked eye detection is ~4 mM, which is below the threshold levels. article info Article history: Received 2 October 2015 Received in revised form 30 November 2015 Accepted 2 December 2015 Available online 17 December 2015 Keywords: Aluminum ion sensors Conjugated polymer-ATP supramolecular complex Naked eye detection abstract A colorimetric Al 3þ sensor based on fluorescence recovery of a conjugated copolymer-ATP complex is proposed. An optimized ratio of two polythiophene (PT) monomers is utilized to synthesize copolymer (CP) that yielded maximized colorimetric response for Al 3þ in deionized (DI) and tap water. The elec- trostatic disassembly of CP-ATP upon addition of Al 3þ led to an evident visual color change. The lowest concentration of Al 3þ for naked eye observation is around 4 mM, which is below the threshold levels in drinking water according to European Economic Community (EEC) standard. Besides, the proposed assay showed a similar response to Al 3þ in tap water. The proposed methodology showed selective and sen- sitive detection for Al 3þ in analytically relevant concentration ranges without involving sophisticated instrumentation, illustrating the applicability for on-site drinking water monitoring. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Metal ions play an important role in living organisms since they are involved in many biological processes such as osmotic regula- tion, catalysis, metabolism, biomineralization and signaling [1]. However, abnormal concentration levels of metal ions might cause detrimental effects, for example, trivalent aluminum (Al 3þ ) in * Corresponding author. Center for Biomimetic Sensor Science, Nanyang Tech- nological University, Singapore 637553, Singapore. ** Corresponding author. Department of Chemistry, Izmir Institute of Technology, Izmir, Turkey. E-mail addresses: hakanyildiz@iyte.edu.tr, yildizuh@stanford.edu (U.H. Yildiz), bliedberg@ntu.edu.sg (B. Liedberg). 1 Equal contribution from authors. Contents lists available at ScienceDirect Analytica Chimica Acta journal homepage: www.elsevier.com/locate/aca http://dx.doi.org/10.1016/j.aca.2015.12.002 0003-2670/© 2015 Elsevier B.V. All rights reserved. Analytica Chimica Acta 912 (2016) 105e110