Latent turn-on fluorescent probe for the detection of toxic malononitrile in water and its practical applications Yuna Jung a, 1 , Nam Kyoo Park a, 1 , Sangrim Kang b, c , Youngbuhm Huh a, c , Junyang Jung a, c , Junho K. Hur a, b, ** , Dokyoung Kim a, c, d, e, * a Department of Biomedical Science, Graduate School, Kyung Hee University, Seoul, 02447, Republic of Korea b Department of Pathology, College of Medicine, Kyung Hee University, Seoul, 02447, Republic of Korea c Department of Anatomy and Neurobiology, College of Medicine, Kyung Hee University, Seoul, 02447, Republic of Korea d Center for Converging Humanities, Kyung Hee University, Seoul, 02447, Republic of Korea e Medical Research Center for Bioreaction to Reactive Oxygen Species and Biomedical Science Institute, Kyung Hee University, Seoul, 02447, Republic of Korea highlights graphical abstract  For the first time we developed a reaction-based fluorescent probe for the detection of toxic malononitrile.  The probe can selectively and sensi- tively detect malononitrile with low detection limit.  The probe can be utilized for the monitoring of residual malononitrile impurities in CS gas.  The probe can be utilized for the fluorescence imaging of malononi- trile in cells. article info Article history: Received 8 August 2019 Received in revised form 5 October 2019 Accepted 9 October 2019 Available online 11 October 2019 Keywords: Molecular probe Malononitrile Bioimaging Sensing Reaction-based probe Cellular imaging abstract A latent turn-on fluorescent probe for the detection of malononitrile (NCCH 2 CN), a precursor of hydrogen cyanide (HCN) in the mammalian tissue metabolism, is developed based on reaction-based fluorophore generation for the first time. Malononitrile is utilized within a wide spectrum of academic and industrial applications, and it is a key reagent to make o-chlorobenzylidene malononitrile (CS gas; tear gas), which is used for riot control. Due to its extensive use as well as potential health risks and the environmental pollution, malononitrile monitoring method has been required. In this paper, we discovered that our key sensing platform, 6-(dimethylamino)-3-hydroxy-2-naphthaldehyde (named Mal-P1), responds sensi- tively and selectively towards malononitrile. The Knoevenagel condensation induced benzo [g]coumarin formation of Mal-P1 with malononitrile showed significant fluorescence turn-on response. In addition, Mal-P1 showed the malononitrile sensing ability in environmental samples (real water, CS gas) and imaging ability in biological sample (HeLa cell line) using fluorescence microscopy with low cytotoxicity. The successful demonstrations will facilitate further applications in a variety of fields. © 2019 Elsevier B.V. All rights reserved. 1. Introduction Malononitrile (NCCH 2 CN), also known as propanedinitrile, is an active dinitrile compound that is useful for the preparation of * Corresponding author. Department of Anatomy and Neurobiology, College of Medicine, Kyung Hee University, Seoul, 02447, Republic of Korea. ** Corresponding author. E-mail addresses: jhur@khu.ac.kr (J.K. Hur), dkim@khu.ac.kr (D. Kim). 1 These authors contributed equally. Contents lists available at ScienceDirect Analytica Chimica Acta journal homepage: www.elsevier.com/locate/aca https://doi.org/10.1016/j.aca.2019.10.015 0003-2670/© 2019 Elsevier B.V. All rights reserved. Analytica Chimica Acta 1095 (2020) 154e161