Novel integrated sensing system of calixarene and rhodamine molecules for selective colorimetric and fluorometric detection of Hg 2+ ions in living cells Bahar Yilmaz, Mukaddes Keskinates, Mevlut Bayrakci ⁎ Karamanoglu Mehmetbey University, Faculty of Engineering, Department of Bioengineering, 70200 Karaman, Turkey abstract article info Article history: Received 31 March 2020 Received in revised form 25 August 2020 Accepted 29 August 2020 Available online 03 September 2020 Three novel and facile calixarene derivatives (5, 6 and 7), which were appended with four rhodamine units at the upper rim of calixarene skeleton, were firstly prepared and evaluated for selective detection of metal ions in so- lution. Receptors (5) and (7) indicated immediate turn on fluorescence output toward Hg 2+ ions over other most competitive metal ions with the ultralow detection limits, indicating their high efficiency and reliability. The binding response to Hg 2+ ions in solution was also observed through a chromogenic change (from colorless to pale pink). Furthermore, in vitro and bio-imaging studies with MCF-7 or MIA PaCa-2 cell lines were also per- formed to investigate the use of receptors in biological systems in order to monitor of mercury ions. Results showed that new receptors (5) or (7) were cell permeable and suitable for real-time imaging of Hg 2+ in living cells (MCF-7) or (MIA PaCa-2) without any damage to healthy cell lines (HEK 293). © 2020 Elsevier B.V. All rights reserved. Keywords: Calixarene Rhodamine Mercury Fluorescence Cell imaging 1. Introduction Mercury is one of the most toxic heavy metals, and can be easily transport via cell membranes in the tissues such as blood-brain, gastro- intestinal tissues, barrier skin and red cell membrane through dissolving in lipid bilayer [1,2]. Even at low concentration, mercury ions cause pri- mary problem for living beings [3,4]. Consequently, selective recogniz- ing and rapid tracking of mercury ions in physiological processes are therefore of paramount importance in order to avoid its harmful effects to living population. Hereby, different techniques such as voltammetry, atomic-absorption spectroscopy (AAS), and inductively coupled plasma emission spectrometry (ICP-AES) are still being investigated for this purpose [5–9]. Among techniques, there is an increasing interest on fluorescent based methods. Therefore, design and synthesis of fluores- cent sensors have been intensively investigated in parallel with this method in recent years. Up till now, a number of fluorescence based methods including the utilization of synthetic or commercial iono- phores, such as azine, hydroxyquinolines, cyclens or cyclams, diazatetrathia crown ethers and calixarenes for Hg 2+ ions have been re- ported in the literature [10–17]. Calixarene based fluorescent sensors are one of the most popular and favored supramolecular structure due to their readily modification and functionalization by ionophore or fluorophore units at lower or upper rim of the calix skeleton [18–20]. However, there are limited number of studies reporting on the applica- tion of calixarenes modified with fluorogenic groups as sensing probe for Hg 2+ . In these studies, while lower rim of the calixarene skeleton (phenolic oxygen units) is usually modified with functional groups, only some of them showed a strong fluorescence response toward Hg 2+ ions with lower selectivity and detection limit. In addition, no sci- entific results on calixarenes modified with strong fluorophore units as rhodamine are reported till now. Rhodamine is a xanthene derivative and a subset of the triarylmethane dyes. Rhodamine molecule as a fluorophore group has some photophysical advantages such as large ab- sorption coefficient, long emission and absorption wavelengths, and high quantum yield. Therefore, there is an increasing interest on design, synthesis and application of rhodamine-based fluorescent sensors due to its particular structure [21,22]. In this study, we modified the upper rim of calixarene skeleton with rhodamine units for the first time by the reaction of para chloromethylated (2), chlorosulfonated (3), and/or formylated (4) calixarene and aminated rhodamine molecule (Rh-A). Therefore, we found three different rhodamine based calixarene molecules (5, 6 and 7) containing an amine, sulfonamide, and azomethine linker, respectively. Herein, we have investigated the sensor applications of three novel rhodamine based calixarene molecules as a selective fluorescence probe toward Hg 2+ ions in solution. Moreover, cytotoxicity experi- ments were conducted to determine the usage of these molecules as an Hg 2+ imaging sensor in healthy cells. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 245 (2021) 118904 ⁎ Corresponding author at: Karamanoglu Mehmetbey University, Department of Bioengineering, 70200 Karaman, Turkey. E-mail address: mbayrakci@kmu.edu.tr (M. Bayrakci). https://doi.org/10.1016/j.saa.2020.118904 1386-1425/© 2020 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa