Читать книгу Diatom Microscopy - Группа авторов - Страница 16

The widespread use of silver nanoparticles (Ag NPs) in industrial applications has prompted concerns about their effects on the environment [1.16]. Researchers have used dark field images to investigate the uptake of Ag NPs by the marine diatoms Cylindrotheca fusiformis and Cylindrotheca closterium and the biological effects on the organisms. As shown in Figure 1.6, Ag NPs detected throughout the diatom cells caused dramatic morphological changes within the cells but had little effect on the cell walls [1.49].

Figure 1.6 Dark field micrographs of control cells and cells exposed to Ag NPs. Ag NPs appear as bright, luminescent spots due to surface plasmon resonance. Scale bar = 10 μm. From [1.49] with permission of John Wiley and Sons.

Figure 1.7 (a) Dark field image of single valve of C. wailesii diatom and (b) corresponding fluorescence macroscopic image. From [1.9] with permission of Hindawi.

At the macroscale, the wide bandgap of amorphous silica does not produce photoluminescence; however, dark field and photoluminescence imaging have shown that nanoscale silica particles exhibit photoluminescence at appropriate excitation wavelengths [1.52]. In addition to photoluminescence from nanostructured silica and diatom frustules, there is also a contribution of organic residuals incorporated in the porous silica matrix. Figure 1.7 presents dark field and green fluorescence images at excitation wavelengths of 450-490 nm [1.9]. It is noted that the photoluminescence process converts the DNA-harmful UV radiation in blue radiation. Due to the maximal efficiency of photosynthesis is in the red spectral region, the green fluorescence appeared in the macroscopy images. These results indicate that there are three mechanisms by which the frustule protects the living diatoms from UV radiation: light absorption, light-collection inhibition and wavelength conversion.