Abstract
Inorganic pollutants in water can have an important impact on ecosystems and human health, so the development of rapid and sensitive detection methods for typical inorganic pollutants in water samples is important for understanding the pollution status of the water environment, as well as water pollution prevention and protection of drinking water safety. Fluorescence sensing technology has the advantages of fast response, high sensitivity, simple operation, and low cost but still has the problems of low quantum yield, cumbersome construction process, and limited practical applications. Based on the excellent fluorescence properties, a series of fluorescence sensing was constructed for the rapid, highly sensitive, and selective detection of various typical inorganic pollutants in water. And the related fluorescence sensing mechanism was investigated in this paper. In this paper, nitrogen/sulfur codoped carbon quantum dots (N, S-CQDs) were prepared for the sensitive and selective detection of sulfide and ferric ion. The blue fluorescent N, S-CQDs were prepared by a one-step hydrothermal method using ammonium citrate and L-cysteine as raw materials, which have excitation wavelength dependence and fluorescence quantum yield of 16.1% for the selective detection of sulfides with a detection limit (S/N=3) of 11.0 nM (about 0.35 μg/L). CQDs with significantly higher fluorescence quantum yields (69%) and no excitation dependence were prepared when citric acid was used instead of ammonium citrate and were used for the selective detection of ferric ion with a detection limit of 14.0 nM (~0.8 μg/L). The method has been successfully applied to the determination of total phosphorus in surface water and human urine, and the fluorescence color change of the dual-emission sensing can be used for the naked-eye identification and semiquantitative detection of phosphate.
Highlights
In recent years, with the continuous development of other related disciplines, fluorescence analysis has been greatly developed in terms of theoretical research and analytical application; a variety of fluorescence analysis methods such as synchronous fluorescence, fluorescence polarization, fluorescence lifetime, time-resolved fluorescence, fluorescence immunoassay, and fluorescence microscopy imaging have been developed successively; and multifunctional fluorescence detection instruments have been introduced one after another [1]
The fluorescence response of N, S-Carbon quantum dots (CQDs)/Eu-Coordination polymers (CPs) dualemission fluorescence sensing for different concentrations of ferric ion is shown in Figure 5; with the increase of ferric ion concentration, the fluorescence intensity at 420 nm gradually decreases; from it, it can be seen that the fluorescence intensity of N, S-CQDs can be linearly related to the ferric ion concentration when the ferric ion concentration is 0.5100.0 μM
It can be seen that ferric ion significantly quenched the fluorescence of N, S-CQDs, while other anions and cations did not affect the fluorescence of N, S-CQDs significantly, indicating that the fluorescence sensing can achieve the selective detection of ferric ion
Summary
With the continuous development of other related disciplines, fluorescence analysis has been greatly developed in terms of theoretical research and analytical application; a variety of fluorescence analysis methods such as synchronous fluorescence, fluorescence polarization, fluorescence lifetime, time-resolved fluorescence, fluorescence immunoassay, and fluorescence microscopy imaging have been developed successively; and multifunctional fluorescence detection instruments have been introduced one after another [1]. The recognition groups can bind or interact with the target analytes, causing fluorescence changes in the fluorophores and outputting fluorescence signals through the fluorescence spectrometer to achieve the determination of the target analytes; fluorescence sensing modified by specific recognition groups can selectively identify the target analytes and achieve the qualitative and quantitative analysis of the target analytes in complex samples [3]. The fluorescence sensing modified with specific recognition groups can selectively identify the target analytes, enabling qualitative and quantitative analysis of the target analytes in complex samples [4]. The fluorescence sensing based on PET mechanism usually consists of three parts: fluorophore (fluorophore), recognition group (receptor), and linker arm (spacer), which mostly contain conjugated structures (naphthalene, pyrene, and anthracene), are responsible for absorbing light energy and emitting fluorescence, and are electron acceptors; the recognition group generally contains N, O, S, and other heteroatoms, which can bind to the target [6]. The linker arm is used for the connection between the fluorophore and the recognition group [7]
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