Contents lists available at ScienceDirect Journal of Photochemistry & Photobiology A: Chemistry journal homepage: www.elsevier.com/locate/jphotochem Ratiometric sensing of sulfite/bisulfite ions and its applications in food samples and living cells Asaithambi Gomathi, Periasamy Viswanathamurthi* Department of Chemistry, Periyar University, Salem, Tamil Nadu, 636011, India ARTICLE INFO Keywords: Ratiometric fluorescent probe Sulfite detection Real sample analysis Live cell imaging ABSTRACT Two novel ratiometric fluorescence probes based on diformyl phenol appended indolium dye (DFIN) and di- formyl bisphenol appended indolium dye (BPIN) were designed and synthesized. The probes DFIN and BPIN exhibited high selectivity towards SO 2 derivatives with fast response time (100 and 120 s). The detection limit of DFIN and BPIN for sulfite ions were 1.8 nM and 2.1 nM which is lower than the maximum acceptable limit of sulfite ion in food samples by United States Environmental Protection Agency (USEPA). Furthermore, the novel ratiometric fluorescent sensors DFIN and BPIN could be used for recognition of sulfite ions in food samples in addition to living cells. 1. Introduction Sulfur dioxide (SO 2 ) is a well-known hazardous pollutant [1], which was predominantly produced from the combustion of coal and fossil fuels in the industries and also it has strong pungent odor [2–5]. Similar to gaseous signaling molecules nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H 2 S), sulfur dioxide was also acknowledged as a new gaseous transmitter generated by sulfur-containing amino acid and it involves numerous physiological process [6–8]. Various epide- miological studies also proved that continual release of SO 2 not only induces neurological disorders [9] and cardiovascular diseases [10] but is also major reason for acidic rain in the environment, which effects series damage to animals, trees, rivers and lakes [11–13]. Additionally, inhaled sulfur dioxide (SO 2 ) could be hydrated and produce it deriva- tives sulfite (SO 3 2– ) and bisulfite (HSO 3 –)[14,15]. Furthermore, SO 2 derivatives (HSO 3 - /SO 3 2- ) are extensively used as a preservative in foodstuff and beverages due to its ability to prevent and controls the growth of microorganisms during production and storage and preserve the stability and potency of pharmaceutical products [16,17]. Despite their advantages in the food and pharmaceutical products, excess concentration level of sulfur dioxide derivatives leads to hypotension, gastrointestinal pain, dermatitis, urticarial, diarrhea, and breathing problems [18,19]. In order to secure the human health, FAO/WHO has declared that the acceptable daily of intake of SO 2 for a healthy human should not exceed 0.7 mg/kg body weight. US Food and Drug Admin- istration (FDA) permits 10 ppm (125 μM) of SO 3 2 ˉ in food and bev- erages [20–22]. Considering these environmental and health problems associated with sulfur dioxide derivatives, it is very essential to develop a reliable method with high sensitivity and selectivity for monitoring trace level of SO 3 2 ˉ/HSO 3 ˉ in the environment as well as in food/ pharmaceutical products [23–25]. Many conventional techniques are reported for recognition of SO 3 2 ˉ/HSO 3 ˉ ions [26–29]. Currently fluorescent method have been widely used over other strategies because of its operational simplicity, fast response, cost-effective, real-time monitoring, high sensitivity and low concentration of analytes [30–32]. In recent years, numerous fluorescent probes were designed for detection of SO 3 2 ˉ/HSO 3 ˉ species. However, now a days researchers prefer ratiometric and near-infrared (NIR) fluorescent probes for monitoring sulfur dioxide derivatives in physiological medium [33]. By comparing single emission probes, ra- tiometric fluorescent probes possesses some advantages like high sen- sitivity, minimize the auto fluorescent interference and produce more precise results. Therefore, due to the above impacts, few ratiometric fluorescent probes for the identification of SO 3 2 ˉ/HSO 3 ˉ ions have been developed by the researchers [5,34–36]. For instance, Ye et al. [37]. developed benzothiazolium based colorimetric and ratiometric fluor- escent probe for HSO 3 -/SO 3 2- ions detection. The probe shows ex- cellent selectivity towards sulfites ion over the other important anions. Sun et al. [38] reported benzo[e]indolium based ratiometric probe, and the probe could quantitatively detect sulfite ions. Song et al. [39]. synthesized coumarin-based reactive sensor for recognition of sulfur dioxide derivatives in water medium. Samanta et al. [40] prepared ratiometric fluorescent probe for tracking of sulfite ions. Yu et al. [7]. developed dual functional ratiometric fluorescent probe for observing https://doi.org/10.1016/j.jphotochem.2019.112214 Received 2 August 2019; Received in revised form 21 October 2019; Accepted 2 November 2019 ⁎ Corresponding author. E-mail address: viswanathamurthi@gmail.com (V. Periasamy). Journal of Photochemistry & Photobiology A: Chemistry xxx (xxxx) xxxx 1010-6030/ © 2019 Elsevier B.V. All rights reserved. Please cite this article as: Asaithambi Gomathi and Periasamy Viswanathamurthi, Journal of Photochemistry & Photobiology A: Chemistry, https://doi.org/10.1016/j.jphotochem.2019.112214