Mercedes Perullini

Silica-alginate-fungi biocomposites for remediation of polluted water

Here we introduce an assembly for bioremediation of polluted water based on the immobilization of alginate beads loaded with filamentous fungus Stereum hirsutum inside nanoporous silica hydrogels. The resulting hybrid device exhibits good physical, chemical and biological stability, being effective in the removal and degradation of malachite green (MG), even in solutions with a high concentration of the dye. This fact is a consequence of adsorption and regulated transport of the dye, as well as the retention of dye degradation enzymes inside the hydrogel. The optimal structure of the hydrogel for an efficient dye–enzyme encounter resulted from the fine adjustment of synthesis conditions in order to achieve a suitable porosity. The results presented here open the possibility of bioremediation without dissemination of exotic organisms to the environment, and can be extended to a vast variety of strains due to the inherent high biocompatibility of the present procedure.

Development of a Biosensor for Environmental Monitoring Based on Microalgae Immobilized in Silica Hydrogels

A new biosensor was designed for the assessment of aquatic environment quality. Three microalgae were used as toxicity bioindicators: Chlorella vulgaris, Pseudokirchneriella subcapitata and Chlamydomonas reinhardtii. These microalgae were immobilized in alginate and silica hydrogels in a two step procedure. After studying the growth rate of entrapped cells, chlorophyll fluorescence was measured after exposure to (3-(3,4-dichlorophenyl)-1,1-dimethylurea) (DCMU) and various concentrations of the common herbicide atrazine. Microalgae are very sensitive to herbicides and detection of fluorescence enhancement with very good efficiency was realized. The best detection limit was 0.1 μM, obtained with the strain C. reinhardtii after 40 minutes of exposure.

Improving silica matrices for encapsulation of Escherichiacoli using osmoprotectors

The development of sol–gel based processes for the encapsulation of living cells is a challenging task where the host material must be optimized both in terms of intrinsic properties and impact on cell viability. Here, the mechanical stability of silica hosts obtained via a mixed aqueous route based on sodium silicate–silica nanoparticle mixtures could be improved by increasing the relative content of molecular precursors over colloidal silica. The specific surface area, pore volume and diffusion properties of the host were also modified. Moreover, this resulted in an increase in the ionic strength, inducing high osmolarity that is detrimental to encapsulated Escherichia coli bacteria. Glycine betaine, a well-known E. coli osmoprotector, could be successfully used as an additive to the sol–gel formulation to limit this osmotic stress. Compared to the previously studied glycerol additive, glycine betaine was found more efficient to preserve the bacterial viability. Moreover, this efficiency was obtained with much lower amounts of glycine betaine, whose addition has therefore no detrimental impact on the silica host structure. These data provide new information about the different cellular stresses resulting from the sol–gel encapsulation process and demonstrate the importance of combining chemical and biological approaches to design more robust functional “living” materials.

Bacteria encapsulation in a magnetic sol–gel matrix

The encapsulation of Escherichia coli bacteria within ferrihydrite gels favours the long-term viability of the entrapped cells while preserving the magnetic properties of the host material.

Sol-gel silica platforms for microalgae-based optical biosensors

An advanced hybrid biosensing platform with improved optical quality is developed based on the acidic encapsulation of microalgi in silica matrices synthesized by TAFR (tetraethoxysilane derived alcohol free route). The three microalgi (Chlorella vulgaris, Pseudokirchneriella subcapitata and Chlamydomonas reinhardtii) were previously immobilized in alginate following the two-step procedure. Tuning the alginate protecting function with the aid of Tris-HCl buffer, the sol-gel synthesis was conducted at pH 4.0 well below the tolerance limit imposed by the encapsulated microalgae. The acidic condensation of Si(IV) generates silica matrices with outstanding optical properties that suit the requirements of biosensors based on optical detection methods.

Improving bacteria viability in metal oxide hostsvia an alginate-based hybrid approach

A two-step process relying on cell encapsulation in alginate beads followed by inorganic gelation from colloidal metal oxides was successfully applied to the immobilization of Escherichia coli bacteria in the presence of boehmite and zirconium oxyhydroxide particles. In the case of the Al-based gel, the alginate bead obtained at low biopolymer content provides an efficient barrier against the encapsulation stress. In contrast, an increase in the alginate concentration together with the phosphate-induced mineralization of the biopolymer bead is found necessary to maintain the viability of entrapped bacteria in Zr-based gels. Diffusion studies using model molecular and colloidal species put in evidence that positively charged Zr-oligomers and ZrO2 nanoparticles may be involved in the cytotoxicity of the precursor solution. This optimization of the encapsulation process allows the first observation of E. coligrowth within such metal oxide–alginate hybrid gels. Results presented in this work give a clear evidence that sol–gel based cell encapsulation can now be envisioned within a wide variety of metal oxide hosts through the optimization of the pre-encapsulation environment.

New method for the simultaneous determination of diffusion and adsorption of dyes in silica hydrogels

The fine tuning of porosity in sol gel based devices makes possible the design of novel applications in which the transport of molecules through the oxide gel plays a crucial role. In this work we develop a new method for the simultaneous analysis of diffusion and adsorption of small diffusing probes, as anionic and cationic dyes, through silica mesoporous hydrogels synthesized by sol-gel. The novelty of the work resides in the simplicity of acquisition of the experimental data (by means of a desk scanner) and further mathematical modeling, which is in line with high throughput screening procedures, enabling rapid and simultaneous determination of relevant diffusion and adsorption parameters. Net mass transport and adsorption properties of the silica based hydrogels were contrasted to dye adsorption isotherms and textural characterization of the wet gels by SAXS, as well as that of the corresponding aerogels determined by Field Emission Scanning Electron Microscopy (FESEM) and N2 adsorption. Thus, the validation of the results with well-established characterization methods demonstrates that our approach is robust enough to give reliable physicochemical information on these systems.

Silica@proton-alginate microreactors: a versatile platform for cell encapsulation

As an alternative approach to the well known Ca(ii)-alginate encapsulation process within silica hydrogels, proton-driven alginate gelation was investigated in order to establish its capacity as a culture carrier, both isolated and embedded in an inorganic matrix. Control over the velocity of the proton-gelation front allows the formation of a hydrogel shell while the core remains liquid, allowing bacteria and microalgae to survive the strongly acidic encapsulation process. Once inside the inorganic host, synthesized by a sol-gel process, the capsules spontaneously redissolve without the aid of external complexing agents. The entrapped cells survive the two-step process to a significant extent; cultures growth restores the initial cell count in less than two weeks. Biosynthesis of Au nanoparticles mediated by the entrapped microalgae illustrates the preservation of the biosynthetic abilities supported by this platform.

Feasibility of using a translucid inorganic hydrogel to build a biosensor using immobilized algal cells

Anthropic activities generate contaminants, as pesticides and other pollutants, in the aquatic environment which present a real threat to ecosystems and human health. Thus, monitoring tools become essential for water managers to detect these chemicals before the occurrence of adverse effects. In this aim, algal cell biosensors, based on photosystem II activity measurement, have been designed for several years in previous studies. In this work, we study a new immobilization technique of algal cells in the aim of improving the performance of these biosensors. Immobilization was here achieved by encapsulation in a hybrid alginate/silica translucid hydrogel. The feasibility of this process was here assessed, and the biosensor designed was tested on the detection of chemicals in urban rainwaters.

Co-encapsulation of Daphnia magna and microalgae in silica matrices, a stepping stone toward a portable microcosm

We report on the first silica encapsulation of a metazoan (Daphnia magna), with a high initial viability (96% of the population remained active 48 h after encapsulation). Moreover, the co-encapsulation of this crustacean and microalgae (Pseudokirchneriella subcapitata) was achieved, creating inside a silica monolith, the smallest microcosm developed to present. This artificial ecosystem in a greatly diminished scale isolated inside a silica nanoporous matrix could have applications in environmental monitoring, allowing ecotoxicity studies to be carried out in portable devices for on-line and in situ pollution level assessment.