Light-Emitting Biosilica by In Vivo Functionalization of Phaeodactylum tricornutum Diatom Microalgae with Organometallic Complexes

In vivo incorporation of a series of organometallic photoluminescent complexes in Phaeodactylum tricornutum diatom shells (frustules) is investigated as a biotechnological route to luminescent biosilica nanostructures. [Ir(ppy)2bpy]+[PF6]−, [(2,2′-bipyridine)bis(2-phenylpyridinato)iridium(III) hexafluorophosphate], [Ru(bpy)3]2+ 2[PF6]−, [tris(2,2′-bipyridine)ruthenium(II) hexafluorophosphate], AlQ3 (tris-(8-hydroxyquinoline)aluminum), and ZnQ2 (bis-8-hydroxyquinoline-zinc) are used as model complexes to explore the potentiality and generality of the investigated process. The luminescent complexes are added to the diatom culture, and the resulting luminescent silica nanostructures are isolated by an acid-oxidative treatment that removes the organic cell matter without altering both frustule morphology and photoluminescence of incorporated emitters. Results show that, except for ZnQ2, the protocol successfully leads to the incorporation of complexes into the biosilica. The spontaneous self-adhering ability of both bare and doped Phaeodactylum tricornutum cells on conductive indium tin oxide (ITO)-coated glass slides is observed, which can be exploited to generate dielectric biofilms of living microorganisms with luminescent silica shells. In general, this protocol can be envisaged as a profitable route to new functional nanostructured materials for photonics, sensing, or biomedicine via in vivo chemical modification of diatom frustules with organometallic emitters.

Optimising extraction of extracellular polymeric substances (EPS) from benthic diatoms: comparison of the efficiency of six EPS extraction methods

There is no universal method that can be applied to extract bound extracellular polymeric substances (EPS) from benthic diatoms of intertidal sediments without causing cell lysis. Six extraction methods were tested on a diatom culture of Navicula jeffreyi to establish the best compromise between high yields of carbohydrate extraction and minimum cell lysis. Extraction with distilled water provoked cell lysis (as already known). The five other extraction methods (dowex resin, artificial seawater of half salinity and extractions after pretreatment with gluteraldehyde by three methods: water, dowex water and dowex buffer) did not provoke cell lysis as shown by transmission electronic microscopy. This result was confirmed by the minimum release of internal compounds (protein, ATP) and by the low proportions of glucose in dowex-extracted EPS compared with the water-extracted EPS, from which the high glucose content must be inferred as contamination by the chrysolaminaran. The extraction with dowex resin resulted in the second-highest concentration of carbohydrate after the water extraction and the EPS were especially rich in deoxy sugars, hence increasing the hydrophobic feature of these substances. For these reasons, we recommend extraction with dowex, which is also the best method for extracting bound EPS from other biofilms such as in activated sludges.