Photoluminescence shift in frustules of two pennate diatoms and nanostructural changes to their pores

Abstract

The diatom silicified cell wall (frustule) contains pore arrays at the micro- to nanometer scale that display efficient luminescence within the visible spectrum. Morphometric analysis of the size and arrangement of pores was conducted to observe whether any correlation exists with the photoluminescence (PL) of two diatom species of different ages. UV-excited PL displays four clearly defined peaks within the blue-region spectrum, on top of the broad PL characteristic of synthetic porous silicon dioxide, recorded for reference and where discrete lines are absent. A set of shifted emission lines was observed when diatom cultures reached adulthood. These discrete line shifts correlate with structural changes observed in adult frustules: reduction in pore diameter; appearance of pores within pores, 10 nm in size; an increase in the gap distance between stria; and the deposition of several girdle bands with a concomitant increase in the diatom waist length, as well as the appearance of pores on such bands. Destruction of the pores results in the disappearance of all discrete emission lines. The PL shifts are correlated with a substantial increment of Si-OH groups adsorbed on the frustule surface, as revealed by Fourier transform infrared spectroscopy.

Frustules of Amphora sp. as a photonic crystal with photoluminescent CdS nanoparticles

“…This interaction between CdS‐NP and frustules was explained as due to both physical van der Waals forces and acid–base interactions; the basic characteristics of NP and the acid characteristics due to the hydroxyl groups (donors of hydrogen bonds) increased because of the roughness of the frustule surface, for example pores and striae. [ 6 ]…”

“…Therefore, frustule structure focusing light as antenna arrays may act as a photonic crystal. [ 5,6 ] A photonic crystal is a periodic array of different refractive indexes materials, scattering visible light in the same way as atomic crystals scatters X‐rays. It is a material in which structural colours are due to the geometrical characteristics and refractive index of microstructured and nanostructured scales.…”

“…It is a material in which structural colours are due to the geometrical characteristics and refractive index of microstructured and nanostructured scales. In our previous work [ 6 ] with the cleansing frustules (without intracellular content) of the pennate diatom Amphora (Ehrenb. ex Kütz 1844) (Figure 1a), we observed nanosized pores within pores of 10 ± 0.7 and 60 ± 4 nm diameter, respectively (Figure 1b), that displayed blue light emission with three distinctive (458, 468, and 486 nm) and three additional small‐amplitude peaks in the green region (499, 510, and 525 nm) under UV excitation at 375 nm.…”

Bioengineered Silicon Diatoms: Adding Photonic Features to a Nanostructured Semiconductive Material for Biomolecular Sensing

“…5b ): in all cases, three main contributions to photoemission under laser excitation were observed. The first one, centered at 380–400 nm (peak 1), came from structural silanols (≡Si–OH), which were both inside and on the surface of the frustules; the intensity of this photoluminescence peak can vary depending on the size of the nanostructures where silanols are activated [ 18 , 22 ]. The second peak at 480–500 nm (peak 2) could be ascribed to surface hydrogenated silicon groups (≡Si–H) [ 23 ].…”

Micro‐photoluminescence of single living diatom cells

“…Nanostructured biosilica from cultured photosynthetic diatom cells has shown to possess photoluminescencent (PL) properties, exhibiting strong blue light emission upon UV excitation . Furthermore, cultivation of diatom cells under controlled delivery of soluble silicon and other trace metals offers a route to make nanostructured diatom silica with controlled PL and electroluminescent properties .…”