Selective Naked-Eye Detection of Hg 2+ through an Efficient Turn-On Photoinduced Electron Transfer Fluorescent Probe and Its Real Applications Priyanka Srivastava, † Syed S. Razi, † Rashid Ali, † Ramesh C. Gupta, † Suresh S. Yadav, ‡,§ Gopeshwar Narayan, ‡,§ and Arvind Misra* ,† † Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221005 Uttar Pradesh, India ‡ Department of Molecular and Human Genetics, Faculty of Science, Banaras Hindu University, Varanasi 221005 Uttar Pradesh, India * S Supporting Information ABSTRACT: A simple molecular fluorescent probe 5 has been designed and synthesized by appending anthracene and benzhydryl moieties through a piperazine bridge. The probe upon interaction with different metal ions showed high selectivity and sensitivity (2 ppb) for Hg 2+ through fluorescence “turn-on” response in HEPES buffer. The significant fluorescence enhancement (∼10-fold) is attributable to PET arrest due to complexation with nitrogen atoms of the piperazine unit and Hg 2+ in 1:2 stoichiometry, in which a naked-eye sensitive fluorescent blue color of solution changed to a blue-green (switched-on). As a proof of concept, promising prospects for application in environmental and biological sciences 5 have been utilized to detect Hg 2+ sensitively in real samples, on cellulose paper strips, in protein medium (like BSA), and intracellularly in HeLa cells. Moreover, the optical behavior of 5 upon providing different chemical inputs has been utilized to construct individual logic gates and a reusable combinational logic circuit. The combinational circuit (switch ON mode; OR logic gate) is easily resettable to the original position (switch OFF mode; INHIBIT logic gate) by applying reset chemical inputs (OH - and PO 4 3- ) with great reproducibility. R ecently, heavy and transition metal (HTM) contamination has brought forth serious environmental and health problems. 1 Among HTMs, mercury (Hg 2+ ) is recognized as a detrimental neurological toxin which is widely distributed in the environment by various natural processes, industrial releases, and anthropogenic activities. 2,3 The bioaccumulation of such toxic material in living tissues of human and animal bodies via a food chain causes mercury poisoning, serious neural disorder, and diseases like Minamata. 1-3 The Environmental Protection Agency (EPA) has set a 2 ppb maximum tolerable level of mercury contamination in drinking water. 2,3 Therefore, considerable current interest has arisen to develop selective and sensitive methodologies for the detection of HTMs owing to their extensive use and ensuing impact on the environment. Many reports dealing with the detection of Hg 2+ show fluorescence quenching 2 because Hg 2+ is known to induce a spin-orbit coupling effect and is spectroscopically and magnetically silent (filled d 10 orbitals). 4 Therefore, the common analytical techniques such as nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) are not adequately competent to detect Hg 2+ in environmental and biological systems. Optical based techniques (fluorescence, phosphorescence, and chemiluminescence) have some obvious real time advantages since they are simple, noninvasive, and highly sensitive. 1 Moreover, progress in development of naked- eye sensitive chemosensors for the detection of HTM ions are increasingly appreciated important aspect since it may offer qualitative and quantitative information. Mercury mediated chemical reactions such as deselenation, hydrolysis, mercura- tion, and also coordination to sulfur containing receptors are some common strategies to develop good fluorescent sensors for mercury; 5,6 however, systems capable to detect Hg 2+ through enhanced fluorescence are rare. 7 While looking for a good sensor motif, particularly for Hg 2+ , the major concern is to achieve good optoelectronic properties, “turn-on” emission, as well as naked-eye sensitive color changes. In contrast to “turn- off” motifs, “turn-on” emission is preferred to enhance detection sensitivity and ease low concentration detection with negligible background. Moreover, the aqueous medium compatibility is another limiting factor and the fluorescence probes to detect Hg 2+ in pure or partial aqueous medium are limited in number. 8-13 Thus, the development of facile and Received: May 5, 2014 Accepted: August 6, 2014 Article pubs.acs.org/ac © XXXX American Chemical Society A dx.doi.org/10.1021/ac501780z | Anal. Chem. XXXX, XXX, XXX-XXX