Handbook of Aggregation-Induced Emission, Volume 2. Группа авторов

Чтение книги онлайн.

Figure 3.11 (A) Fluorescence spectra of 18 (20 mM) upon the addition of different concentrations of Al³⁺ (0–500 mM) in 10 mM HEPES buffer at pH 7.0 (containing 0.2% DMSO). Excitation wavelength is set at 370 nm. (B) Calibration curve based on the ratio of fluorescence intensities (I₄₆₁/I₅₃₇) as a function of Al³⁺ concentrations; error bar represents three repeated experiments. (C) Fluorescence intensity ratio (I₄₆₁/I₅₃₇) of 18 (20 mM) upon the addition of 500 mM metal ions in 10 mM HEPES buffer at pH 7.0 (containing 0.2% DMSO). Ions from 1 to 18: blank, Li⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺, Ba²⁺, Sr²⁺, Fe²⁺, Fe³⁺, Co²⁺, Cu²⁺, Hg²⁺, Ag⁺, Cd²⁺, Mn²⁺, Ga³⁺, and Al³⁺. (D) Confocal fluorescence images of live HeLa cells. (a–d) The cells were incubated with 18 (5.0 mM) for 30 minutes; (e–h) the above cells upon the addition of 200 mM Al³⁺ were then incubated for another 20 minutes; (a) and (e) bright‐field transmission images; (b) and (f) blue channel images at 429–469 nm; (c) and (g) yellow channel images at 511–611 nm; (d) and (h) ratio images generated from (b) and (c) and (f) and (g), respectively. The excitation was set at 405 nm.

      Source: Reprinted from Ref. [26] (Copyright 2014 Elsevier B.V.).

The detection of inorganic species such as CN⁻, F⁻, UO₂²⁺, S²⁻, and ClO⁻ is of great significance in environment, biology, and industry. Cyanide (CN⁻) is one of the most powerful poisons. It affects vascular, vision, cardiac, endocrine, and metabolic functions and causes fatal damage to the nervous system. The fluoride ion (F⁻) is very useful in the treatment for osteoporosis and orthodontics. However, excess F⁻ leads to fluorosis, which results in the increment in the bone density. Taking the advantage of hydrogen bonding with the hydroxyl group of SSB, the detection of such basicity anions like CN⁻ and F⁻ is facile by SSB fluorescent probes with high sensitivity and satisfactory selectivity. As shown in Figure 3.12a and b, after adding CN⁻, probe 20 undergoes deprotonation due to the basicity of CN⁻. Cyclization reaction occurred under the catalysis of CN⁻, and the corresponding benzoxazole formed gradually in this process, therefore lighting up the fluorescence [34]. The detection limit is 5.92 × 10⁻⁷ M, lower than the WHO guideline of CN⁻ in drinking water (1.9 μM). The competitive experiments reveal high sensing selectivity and sensitivity of 20 for CN⁻ over other anions (Figure 3.12c). Test papers were also prepared for the practical application of cyanide detection. By influencing hydrogen bonding, SSB‐based fluorine ion fluorescent probes were also reported. Figure 3.12d lists some SSB probes for F⁻ detection. The possible processes and mechanisms are proposed, as demonstrated in Figure 3.12e. The addition of F⁻ resulted in a blue‐shifted emission, which was increasing gradually with an increasing concentration of F⁻. This change was explained by the disruption of the existing six‐membered hydrogen bonding, involving the hydroxyl group and imine nitrogen, which allow the ESIPT process through deprotonation of the phenolic hydroxyl group. Excellent experimental results of detection limits and selectivity over other anions were also obtained in real sample detection (Figure 3.12f, g).

Chen et al. reported a fluorescence turn‐on SSB probe 25 for uranyl ion (UO₂²⁺) detection with high efficiency [32]. As one of the radioactive metal elements, uranium is an important raw material for the nuclear industry. At present, uranium‐based nuclear power facilities have gradually increased their proportion in power generation facilities in various countries. Metal uranium is extremely radioactive and chemically toxic, with a half‐life of hundreds of millions of years, which can cause lasting disturbances and damage to the immune, reproduction, and hematopoietic systems of the organism. Uranyl ion (UO₂²⁺) is the most commonly existing formation of uranium in natural water; therefore, the detection of UO₂²⁺ in water is of great significance for the assessment of water pollution. As illustrated in Figure 3.13a, 25 undergoes a complex interaction and forms aggregates with the addition of UO₂²⁺, exhibiting a fluorescence enhancement at 540 nm, which was linearly related to the concentration of UO₂²⁺ in the range of 1–25 ppb. The limit of detection was achieved as low as 0.2 ppb with a relative standard deviation (RSD) of 1.3% (Figure 3.13b, c). Such a detection method was successfully utilized in quantifying UO₂²⁺ in fuel processing wastewaters. Other fluorescent probes based on salicylaldehyde azine derivatives for the detection of sulfur(38) (S²⁻), hypochlorite(37) (ClO⁻), and so on were also developed by the modification of a metal complex of SSB.

In addition to necessary metal ions and nonmetal ions, a number of biologically small molecules are also important components to maintain the normal metabolic activities of complex biological organisms. For instance, pyrophosphate ion (PPi) is an important biologically related inorganic species, which plays an important role in the synthesis of DNA, RNA, and proteins and in life activities such as signal transduction. Studies have shown that the occurrence of arteriosclerosis and osteoarthritis is closely related to abnormal pyrophosphate levels in human body. In recent years, the analysis and detection of pyrophosphate have attracted increasing attention of scientists. Pyrophosphate has a strong coordination with Cu²⁺. Most fluorescent detection methods for pyrophosphate are based on this principle. Due to the superior coordination ability of SSB and Cu²⁺, SSB–copper(II) complex is therefore very suitable for the design and synthesis of pyrophosphate probes. As Figure 3.14a shows, Tong and coworkers developed a facile PPi fluorescence turn‐on probe 26 of copper(II) complex [39]. The AIE fluorescence of 26 was completely quenched due to the coordination of Cu²⁺. The complexation of PPi with Cu²⁺ resulted in the release of free 26, which reaggregated in the solution and recovered the orange fluorescence. Figure 3.14b reveals good selectivity of the probes with other common anions. The fluorescent signal enhancement showed excellent linear relationship with a PPi concentration range of 0–15 μM, and the detection limit was obtained as 0.064 μM.