Optical microalgal biosensors for aqueous contaminants using organically doped silica as cellular hosts.

Optical biosensors for the detection of toxic species in aqueous media were developed via the encapsulation of microalgae in sol-gel matrices. In a first step, the effect of cadmium(II), lead(II), and anthracene on the chlorophyll a fluorescence intensity of Anabaena flos-aquae, Chlorella vulgaris, and Euglena gracilis microalgae in suspension was studied. Complementary ATP-metry measurements demonstrated a direct relationship between optical response and pollutant toxicity, in a cell- and dose-dependent manner. In a second step, microalgae were successfully encapsulated in silicate-colloidal silica nanocomposite matrices. However, a complete loss of cell response to pollutant addition was observed, despite the preservation of cell viability. Introduction of a low amount (5 mol%) of amine- or ethyl-bearing silanes in the matrix formulation allowed the recovery of the sensing capacity of the immobilized microalgae, without impacting on the response time (30 s). Porosimetry and 29Si solid-state NMR spectroscopy showed that the organic moieties are fully integrated into the inorganic network, tuning the ability of the target pollutant to diffuse and reach the encapsulated algae. This versatile strategy could be useful for the easy and fast assessment of contamination levels in polluted waters. Graphical Abstract Microalgal biosensors for aqueous contaminants using organically doped silica as cellular hosts.

The physics and chemistry of silica-in-silicates nanocomposite hydrogels and their phycocompatibility.

Silicates-in-silica nanocomposite hydrogels obtained from sodium silicates/colloidal silica mixtures have previously been found to be useful for bacterial encapsulation. However the extension of synthesis conditions and the understanding of their impact on the silica matrix would widen the applicability of this process in terms of encapsulated organisms and the host properties. Here the influence of silicates and the colloidal silica concentration as well as pH conditions on the gel time, the optical properties, the structural and mechanical properties of silica matrices was studied. We show that gel formation is driven by silicate condensation but that the aggregation of silica colloids also has a major influence on the transparency and structure of the nanocomposites. Three different photosynthetic organisms, cyanobacteria Anabaena flos-aquae and two microalgae Chorella vulgaris and Euglena gracilis, were used as probes of the phycocompatibility of the process. The three organisms were highly sensitive to the silicate concentration, which impacts both the gelation time and ionic strength conditions. The Ludox content was crucial for cyanobacteria as it strongly impacts the Young's modulus of the matrices. The detrimental effect of acidic pH on cell suspension was compensated by the silica network. Overall, it is now possible to select optimal encapsulation conditions based on the physiology of the targeted cells, opening wide perspectives for the design of biosensors and bioreactors.

Sol-gel encapsulation of biomolecules and cells for medicinal applications.

The sol-gel process provides a robust and versatile technology for the immobilization of biologicals. A wide range of inorganic, composites and hybrid materials can be prepared to encapsulate molecular drugs, proteins, antibodies/antigens, enzymes, nucleic acids, prokaryotic and eukaryotic cells into bulk gels, particles and films. This review describes the applications of sol-gel encapsulation relevant to medicinal chemistry focusing on the recent development of biosensors as well as systems for production, screening and delivery of bioactive compounds and biomaterials.