A facile dual-function fluorescent probe for detection of phosgene and nitrite and its applications in portable chemosensor analysis and food analysis
Graphical abstract
Introduction
Phosgene (COCl2) is one of chemical warfare agent (CWA) that was widely used in World War I and World War II, and the toxic gas bombs manufactured by it caused huge casualties [[1], [2], [3], [4]]. Phosgene can quickly bind to proteins in the alveoli after inhaled by people and affect normal breathing. When exposed to phosgene at a concentration of 20 ppm or above for 20 min, the lungs of human will be seriously injured (such as pulmonary edema and emphysema) or even cause death [5]. In addition, due to the active properties of phosgene and low production costs, it is also the important raw materials for industrial production of different type pesticides (including isocyanates, chloroformates, sulfonylureas insecticides and herbicides). Therefore, in the context of the widespread application of phosgene, it is inevitable that phosgene will leak in the industrial production process, or if terrorists use phosgene as a chemical weapon to carry out terrorist activities, which will seriously affect public health and safety. Nitrite (NO2−) is one of the most common nitrogen-containing compounds widely present in the human environment and plays an important role in the production of organic synthesis, agricultural chemicals, pharmaceuticals and many other industrial products [[6], [7], [8], [9]]. However, nitrite is also a kind of food toxic substance and water pollutant, which is harmful to human and aquatic life. Excessive amounts of nitrite in water can cause fish and other aquatic organisms to die of hypoxia [10]. Nitrite in food is generally found in meat products, preserved food and drinking water [11]. Because nitrite can interact with amines in the digestive tract, highly carcinogenic N-nitrosamine compounds will produce when people consume foods that contain nitrite [12]. In addition, it may cause diseases such as infant methemoglobinemia and the central nervous system birth defects [13,14]. Therefore, the development of a simple and effective technique for detecting phosgene and nitrite is extremely important for public health and safety.
The detection methods for phosgene and nitrite that have been reported in recent years are mainly chromatography [15,16], colorimetry [17,18], electrochemical methods [19,20] and fluorescence detection methods [21,22]. However, the use of organic small molecule fluorescent probes to detect ions or molecules has the advantages of simple operation, cheaper equipment, lower limit of detection, and higher selectivity than the above methods. There have been many literatures about the detection of phosgene [[23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49], [50], [51], [52], [53]] and nitrite [[54], [55], [56], [57], [58], [59], [60], [61]] by using small organic fluorescent probes (the comparisons of some details about them has been shown in Figs. S1 and S2 and Tables S1 and S2). Among these reported probes, o-phenylenediamine is a classical recognition group for phosgene [28,31,33,37,41,52] or nitrite [54,55]. In recent years, new advances have been made in recognition groups for the two analytes. For phosgene detection, the structure of 2-(o-substituted phenyl)-1H-imidazole and analogues gradually drew attentions of researchers [23,43,44,51]. For example, Wu et al. used 2-(1H-Phenanthro [9,10-d]imidazole-2-yl)Phenol (Pi) as a ratiometric fluorescent probe for sensing phosgene in solution and gas phase. After reacting with phosgene, the hydroxyl oxygen and imidazole nitrogen are locked by the carbonyl group and thus block rotation of C–C bond, the increase of rigid plane structure causes the switching of fluorescence signal [43]. The nitrite can facilitate o-phenylaniline analogues to form six-membered cyclic structure, which had also been employed to develop fluorescent probes for nitrite detection [58,59]. Recently, Gu et al. reported that o-imidazolylaniline can also undergo the similar cyclization process, and they successfully used 2-(1H-Phenanthro [9,10-d]imidazole-2-yl)Aniline (PA) as probe to detect nitrite in water and food samples [60]. These inspiring works lead our interest focus on the structure of 2-(1H-Benzimidazol-2-yl)Aniline (BMA in Scheme 1). The facile BMA is easily prepared and even commercial available, and BMA implies a more exciting possibility for a dual-function fluorescent probe.
In this work, we first proposed the application of a facile dual-function fluorescent probe BMA for the detection of phosgene and nitrite in different solvent environments. The response of BMA to phosgene in solution performed a ratiometric fluorescent emission change from 416 nm to 480 nm and the limit of detection was 1.27 nM; The response of BMA to nitrite in solution showed a turn-off fluorescent emission change at 485 nm and the limit of detection was 60.63 nM. In addition, we have successfully applied the portable chemosensors (BMA-loaded TLC plates and test strips) to the detection of phosgene in the gas phase and the detection of nitrite in solution, which showed high selectivity and sensitivity. Most importantly, we have successfully applied the probe BMA to the detection of nitrite in food samples. All above characteristics showed that BMA had good application potential.
Section snippets
Reagents and instruments
All reagents were commercially purchased from Aladdin-Reagent (China) and used directly without further purification. Except acetonitrile is HPLC grade, all of the reagents are A.R. grade. The distilled water was purchased from Watsons (China), which pH was 5.2 and conductivity was 2.3 μs cm−1. 1H NMR and 13C NMR spectra were measured with AMX-500 NMR spectrometer (Bruker, Germany). High resolution mass spectra (ESI as the source) were acquired on Q-TOF 6540 LC/MS spectrometer (Agilent, USA).
Selection of solvent environment for sensing phosgene and nitrite
First we explored the effect of different solvents on the fluorescence spectra of BMA. As shown in Fig. S12a, BMA generated two emission peaks due to its own excited state intramolecular proton transfer (ESIPT) action, the enol-form structural emission peak was at about 416 nm, and the keto-form structural emission peak was at 550 nm. As the polarity of the solvents increased, the intensity of the emission peak of the enol-form structure increased and the intensity of the keto-form structure
Conclusion
In summary, we reasonably proposed the application of a facile dual-function fluorescent probe BMA for detecting phosgene and nitrite in different solvent environments. This method had good sensitivity and selectivity and the limit of detection for phosgene in solution was as low as 1.27 nM, while the limit of detection for nitrite was 60.63 nM. We have also made portable chemosensors (BMA-loaded TLC plates and test strips) for detection of phosgene in the gas phase and nitrite in solution,
Notes
The authors declare no conflict of interest.
CRediT authorship contribution statement
Lei Yang: Methodology, Software, Formal analysis, Investigation, Writing - original draft, Writing - review & editing. Feng Wang: Validation, Visualization. Jie Zhao: Formal analysis, Investigation, Visualization. Xiaojian Kong: Resources, Data curation, Project administration. Ke Lu: Investigation, Visualization. Mian Yang: Investigation, Visualization. Jin Zhang: Investigation, Visualization. Zhiwei Sun: Conceptualization, Methodology, Resources, Writing - review & editing, Supervision,
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
We are grateful the financial support from the National Natural Science Foundation of China (No. 21305076 and 21976105), project ZR2019MB005 supported by Shandong Provincial Natural Science Foundation.
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