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

Чтение книги онлайн.

Figure 3.17 (a) Synthesis and schematic presentation of the ratiometric fluorescence change of 29 upon binding to the hydrophobic pocket of BSA. The emission wavelength of 29 changes from 436 to 518 nm. (b) Photographs of 29 before and after the addition of various kinds of proteins under a UV lamp (365 nm). (c) Fluorescence spectra of 29 (10 mM) upon the addition of various concentrations of BSA in 10 mM PBS buffer at pH = 7.4. Excitation wavelength was set at 363 nm. (d) Ratiometric calibration curve of I₅₁₈/I₄₃₆ as a function of BSA concentrations.

      Source: Reprinted from Ref. [44] (Copyright 2013 Royal Society of Chemistry).

There is also an indirect approach to detect enzymes like β‐lactamase, an important bacterial enzyme for some kinds of bacteria resistant to β‐lactam antibiotics (penicillins, cephalosporins, etc.), by cleaving the amide group with high catalytic efficiency [46]. The detection method contains three steps for fluorescence lighting‐up. As Figure 3.19a illustrates, β‐lactamase reacts with the lactam of its substrate (cefazolin sodium) to produce a secondary amine, initiating a spontaneous elimination reaction and affording a thiol compound. The thiol could further react with the sulfonate group of probe 32, releasing the SSB derivative with both AIE and ESIPT characteristics. The fluorescent signal enhancement relates linearly in the range of 0–10 mU/ml, and the detection limit was 0.5 mU/ml. This indirect method was also successfully applied to testing paper fabrication and achieved good analytical performance.

Figure 3.18 (a) Fluorescent light‐up probe 30 for β‐galactosidase detection. (b) Fluorescence spectra of 30 (100 μM) in the presence of various concentrations of β‐galactosidase in the PBS buffer solution and calibration curve of the fluorescence intensities (I₅₄₅) versus β‐galactosidase concentrations. Insets from left to right: photographs of 30 (100 μM) without or with β‐galactosidase under UV light (365 nm). (c) Imaging β‐galactosidase activity in cells. Images of probe 30 (50 μM) in C6/LacZ cells and HeLa cells for two hours at 37 °C.

      Source: Panels (a–c) are adapted permission from Ref. [45] (Copyright 2015 Royal Society of Chemistry).

      (d) Fluorescent light‐up probe 31 for sensing of esterase. (e) Fluorescence spectra of 31 (100 μM) in the presence of various concentrations of esterase (0–1.0 U/ml) in a 10 mM PBS buffer solution and calibration curve of the fluorescence intensities (I₅₈₀) versus esterase concentrations at pH 7.4, 37 °C. Insets from left to right: photographs of 31 (100 μM) without or with esterase under UV light (365 nm). (f) Confocal fluorescent image of MCF‐7 cells with incubation of 31 (50 μM) for 10 minutes or preincubated with a 10 mM inhibitor for 20 minutes and then treated with 31 (50 μM) for 10 minutes.

      Source: Panels (d–f) are reprinted from Ref. [47] (Copyright 2017 American Chemical Society).

Figure 3.19 (a) An indirect approach for fluorescence light‐up detection of β‐lactamase using probe 32. (b) Photographs of test papers under a UV lamp (365 nm) for the detection of β‐lactamase at various concentrations (0–7.0 mU/ml) in the PBS solution containing cefazolin sodium (4.8 mM). (c) The corresponding fluorescence intensity of spots read by Image J software versus the concentrations of β‐lactamase. (d) Calibration curve for β‐lactamase detection.

      Source: Reprinted from Ref. [46] (Copyright 2018 Royal Society of Chemistry).

A polysaccharide SSB sensor for facile, sensitive, and selective heparin detection has also been fabricated [48]. Heparin is a mucopolysaccharide composed of D‐β‐glucuronic acid and N‐acetylglucosamine to form a repeating disaccharide unit. Its skeleton has many anionic groups (such as carboxyl and sulfonic acid groups, etc.), making heparin highly negatively charged. As a medicinal anti‐hemagglutinating agent as well as a special antidote, heparin is hence of great significance for analytical detection. As shown in Figure 3.20a, salicylazine 33 is modified with two positively charged tertiary amine groups, which can be combined with negatively charged heparin through a charge–charge interaction. The emission of probe 33 in the Tris‐HCl buffer solution at pH 7.0 was extremely weak may be and its emission at 530 nm increased rapidly upon the addition of heparin (Figure 3.20b), which was due to the aggregation through electrostatic interactions. When the concentration of heparin reached 22 μg/ml, a fluorescence enhancement of about 40‐folds had been detected. The linear range is 0.2–14 μg/ml, the detection limit is 57.6 ng/ml, and the response time is as short as 2 minutes. Figure 3.20c also represents good selectivity of probe 33 for heparin from other polysaccharides such as chondroitin sulfate (ChS), hyaluronic acid (HA), and dextran (DeX).

Figure 3.20 (a) Design principle of the fluorescence turn‐on detection of heparin based on AIE characteristics of 33. (b) Fluorescence spectra of 33 in the presence of different amounts of heparin (from 0 to 22 μg/ml), λ_ex = 391 nm. (c) The fluorescence intensity of 33 in the presence of different amounts of HA, DeX, ChS, and heparin.

      Source: Adapted with permission from Ref. [48] (Copyright 2013 Elsevier B.V.).

       3.2.3 Ratiometric pH Probes

      As one of the key parameters, pH plays a crucial role in all life forms including external environment as well as cellular functions. Small changes in the pH of the environment may even affect the lives of many plants and animals. In addition, pH is a key factor in pharmaceuticals, food, and drinking water. For intracellular pH, the fluctuation has a significant effect on cell growth, enzyme activity, and ion transport. pH is also one of the important parameters to distinguish cancer cells from normal cells. Therefore, monitoring pH is critical to maintaining our living environment and improving the quality of our life.

      The hydroxyl groups of SSB experience deprotonation according to the increase of medium pH; thus, most SSB AIE fluorophores show significant fluorescent wavelength change, usually blue‐shifted as pH increases [49–53]. Therefore, СКАЧАТЬ