Dual-channel responsive fluorescent sensor for the logic-controlled detection and bioimaging of Zn2+ and Hg2+

https://doi.org/10.1016/j.molliq.2021.115279Get rights and content

Highlights

  • A novel dual-channel responsive fluorescent probe RHI for Zn2+ and Hg2+ was developed.

  • The limits of detection of RHI are down to 82.2 nM for Zn2+ and 1.13 μM for Hg2+.

  • Reversible switching response is acquired by alternate addition of S2−.

  • RHI offers many logic design such as digital magnitude comparator, sequential and memory functions for Zn2+ and Hg2+.

  • The practical performance of RHI was successfully tested in water samples and in Human colon (DDL-1) cells.

Abstract

The fluorescence sensing of specific cationic species is necessary and crucial due to their numerous potential effects on living organisms and the environment. In the present investigation, an efficient dual-channel responsive novel probe based rhodamine 6G condensed isophorone moiety (RHI) was designed and synthesized for sensitive, rapid and specific sensing of metal ions. RHI enabled selective and quick recognition of Zn2+ and/or Hg2+ in the presence of other tested metal ions in EtOH/H2O (8/2, v/v). It demonstrated remarkable red for Zn2+ or yellow emission enhancement for Hg2+ and good photochromism. Addition of S2− to a solution of RHI-M2+ reversed the process, followed by quenching emission, enabling reversible use of RHI. It was able to detect the levels of Zn2+ and Hg2+ within the limit of detection of 82.2 nM and 1.13 μM, respectively. Measurements of mineral and tap water samples prove the potential of the probe RHI for the detection of Zn2+ and Hg2+ ions in environmental aqueous samples. Dual-channel fluorescence response of RHI for Zn2+ and Hg2+ ensured a chance to apply them for build simple or complex molecular logic circuits. Moreover, it could easily visualize Zn2+ or Hg2+ in DDL-1 cells in bioimaging experiments.

Introduction

The heavy metal level in wastewaters increases with the intense use of metals and chemicals in developing industries. This poses great risks both in terms of human health and protecting the ecological balance [1,2]. Many examples such as mixing of harmful substances into air, water and soil through the natural phenomena such as rain and snow, mixing of domestic wastewater into soil and water, increasing amount of petroleum derivatives and solid waste materials spilled into the sea and especially heavy metal industries polluting soil and water disrupt the nature and threat lively life. Heavy metals tend to accumulate in living organisms as well as their toxic and carcinogenic effects [[3], [4], [5]]. Therefore, accumulation increases the importance of heavy metal concentrations still more.

Mercury is a toxic metal that has been scientifically identified in the 15th century as being harmful to human health [6]. Today, mercury and its compounds are used as catalysts in the production of synthetic industrial materials such as acetaldehyde and vinylchloride, as electrodes in the production of chlorine from sodium chloride, in the production of thermometers and electrical instruments, in industrial control devices, as a fungicide in agriculture, in paint and paper industries as well as in many areas of our daily life [7,8]. It is not found in human tissues and is thought that any amount is not required for the body [9]. It exists in nature as an element alone or as mercury compounds. It enters the body through direct contact with the skin and eyes, through the digestive and respiratory system [10]. Moreover, it also passes to the baby through the placenta during pregnancy or breastfeeding milk [11]. The type and severity of mercury poisoning depend on its form and exposure type due to its different toxicodynamic and toxicokinetic properties. All chemical forms of it can cause toxic findings [7,12,13]. In severe poisonings, the nervous system, respiratory system, immune system, kidneys, mouth, teeth, gums and skin are affected [[14], [15], [16], [17]]. The main toxic effect of it begin with the reacting with sulfhydryl groups followed by causing pathological changes in the cell membrane, enzyme inhibition, transport mechanisms and dysfunction in structural proteins [18,19]. Exposure to it during pregnancy can lead to serious congenital defects and impair myelin formation [20]. Mercury poisoning is also considered among the causes of autistic behavior [21].

Zinc is a significant trace element in terms of human health and diet, which can be taken into the body with the consumption of both vegetable and animal foods [22,23]. It is involved in the metabolic activity of many enzymes in the body [24,25]. Moreover, it is effective in cell division, DNA and protein synthesis. Thus, enzymes contribute to energy metabolism and help the use of macronutrients such as fat, protein and carbohydrates that give energy to the body. Due to its contribution to the growth and development process, sufficient zinc intake is important because its deficiency is one of the important reasons of growth retardation in children [26,27]. Upon the bioavailability of zinc decreases, loss of appetite, decreased sense of taste and smell, and late healing of wounds occurs [[28], [29], [30]]. Cell damage by oxidative reactions is prevented by zinc in the cell membrane [31,32]. However, acute poisoning is also encountered with zinc sulfate powders and vapors [33]. It can cause digestive and respiratory irritation symptoms, fever, dyspnea, bronchospasm, pneumonia and collapse in children and sometimes adults [34]. Therefore, the determination of the organism's exposure extent to metal and the level of environmental contamination and the investigation of its health effects is very important.

General methods used in determination of trace elements are atomic absorption spectrometry [35,36], ion chromatography [37,38], induced plasma-atomic emission spectrometry [39,40], voltammetry [41,42]. Unfortunately, most of these techniques involve laborious and time-consuming sample preparation steps and require expensive and huge devices. However, the fluorescence method allows direct determination and offers cheap and on-line assays. Up to now, many fluorescence sensors have been reported for the determination of zinc [[43], [44], [45], [46], [47], [48]] and mercury ions [[49], [50], [51], [52], [53], [54]], separately. However, the number of multi responsive sensors that have the ability to detect both Zn2+ and Hg2+ is quite limited [[55], [56], [57], [58], [59], [60], [61]]. However, some of these fluorescent sensors possess some disadvantages in view of low selectivity [[62], [63], [64]], non “turn-on” response [[65], [66], [67]] and working in anhydrous media [65,66]. Therefore, it is clearly seen that the existing features of multi responsive sensors need to be improved. To address this, we report a novel probe RHI based on rhodamine and isophorone, which displays excellent sensing properties and multi turn-on response to Zn2+ and Hg2+ ions through different sensing mechanisms.

Section snippets

Material and method

Probe RHI was characterized by TOF-MS (Agilent 6230), NMR (Varian 400 MHz) and FTIR (Bruker instrument using ATR method) techniques. 1H NMR spectra were measured in DMSO‑d6 or CDCl3 solvents, and the chemical shifts were reported as δ (ppm). The emission spectra were obtained by excitation at 500 nm (slit 5 nm) on a Perkin Elmer LS 55 spectrophotometer. UV–vis measurements were also realized on a Shimadzu 1280 equipment. All the spectroscopic measurements were conducted at room temperature.

Synthesis of probe RHI

After building blocks including rhodamine 6G-hydrazide (1) and the aldehyde derivative (2) of 5-bromophenol integrated isophorone unit were produced according to known procedures, probe RHI was obtained by the condensation reaction between compound 1 and 2 in 67% of yield (Scheme 1). The structure of RHI was simply confirmed by the disappearance of aldehyde proton signal (CHO) at δ 10.03 ppm of compound 2 and the appearance of an imine proton signal (CH=N) at δ 8.35 ppm in 1H NMR spectra. In

Conclusion

In summary, it was successfully developed a novel dual-channel responsive fluorescent probe RHI based on rhodamine 6G and isophorone moiety for multi-color detection of Zn2+ and Hg2+. Upon interaction of RHI with Zn2+ and Hg2+, distinctly different red or yellow “turn-on” emission responses are observed with respect to other interfering ions. RHI can readily detect Zn2+ and Hg2+, with high selectivity and low detection limits (82.2 nM and 1.13 μM). By the qualitative detection of Zn2+ and Hg2+

Declaration of Competing Interest

The authors declare no financial and personal conflicts of interest.

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