Nanoarchitectonics to entrap living cells in silica-based systems: encapsulations with yolk-shell and sepiolite nanomaterials

In the present work, the bottom-up fabrication of biohybrid materials using a nanoarchitectonics approach has been applied to entrap living cells. Unicellular microorganisms, that is, cyanobacteria and yeast cells, have been immobilized in silica and silicate-based substrates organized as nanostructured materials. In a first attempt, matrices based on bionanocomposites of chitosan and alginate incorporating sepiolite clay mineral and shaped as films, beads, or foams have been explored for the immobilization of cyanobacteria. It has been observed that this type of biohybrid substrates leads to serious problems regarding the long-time survival of the encapsulated microorganisms. Alternative procedures using silica-based matrices with low sodium content, generated by sol-gel methods, as well as pre-synthesised yolk-shell bionanohybrids have been studied subsequently. Optical microscopy and SEM confirm that the silica shell microstructures provide a reduced contact between cells. The inorganic matrix increases the survival of the cells and maintains their bioactivity. Thus, the encapsulation efficiency is improved compared to the approach using a direct contact of cells in a silica matrix. Encapsulated yeast produced ethanol over a period of several days, pointing out the useful biocatalytic potential of the approach and suggesting further optimization of the present protocols.

Silica Hydrogels as Entrapment Material for Microalgae

Despite being a promising feedstock for food, feed, chemicals, and biofuels, microalgal production processes are still uneconomical due to slow growth rates, costly media, problematic downstreaming processes, and rather low cell densities. Immobilization via entrapment constitutes a promising tool to overcome these drawbacks of microalgal production and enables continuous processes with protection against shear forces and contaminations. In contrast to biopolymer gels, inorganic silica hydrogels are highly transparent and chemically, mechanically, thermally, and biologically stable. Since the first report on entrapment of living cells in silica hydrogels in 1989, efforts were made to increase the biocompatibility by omitting organic solvents during hydrolysis, removing toxic by-products, and replacing detrimental mineral acids or bases for pH adjustment. Furthermore, methods were developed to decrease the stiffness in order to enable proliferation of entrapped cells. This review aims to provide an overview of studied entrapment methods in silica hydrogels, specifically for rather sensitive microalgae.

Transferring the Selectivity of a Natural Antibody into a Molecularly Imprinted Polymer

Natural antibodies are widely used for their unprecedented reproducibility and the remarkable selectivity for a wide range of analytes. However, biodegradability and the need to work in biocompatible environments limit their applications. Molecularly imprinted polymers are a robust alternative. While molecularly imprinted polymers have shown remarkable selectivities for small molecules, large structures as proteins, viruses or entire cells are still problematic and flexible structures are virtually impossible to imprint. We have developed a method to form a polymeric copy of the antibodies instead. This book chapter aims to summarize the progress with this technique. To make it easier for other scientists to use this methods I critically discuss advantages and drawbacks of the method compared to alternative techniques. The discussion should help to identify for which applications this technique would be valuable. Finally, I provide a practical guide to use this new method. I highlight potential problems and give hints for possible improvements or adaptations for different applications.

Spontaneous and specific binding of enterohemorrhagic Escherichia coli to overoxidized polypyrrole-coated microspheres

Specific identification of enterohemorrhagic Escherichia coli was achieved using microspheres coated with overoxidized polypyrrole.

Biosorption of Cu(II) by immobilized microalgae using silica: kinetic, equilibrium, and thermodynamic study

Immobilized microalgae using silica (IMS) from Micractinium reisseri KGE33 was synthesized through a sol-gel reaction. Green algal waste biomass, the residue of M. reisseri KGE33 after oil extraction, was used as the biomaterial. The adsorption of Cu(II) on IMS was tested in batch experiments with varying algal doses, pH, contact times, initial Cu(II) concentrations, and temperatures. Three types of IMSs (IMS 14, 70, and 100) were synthesized according to different algal doses. The removal efficiency of Cu(II) in the aqueous phase was in the following order: IMS 14 (77.0%) < IMS 70 (83.3%) < IMS 100 (87.1%) at pH 5. The point of zero charge (PZC) value of IMS100 was 4.5, and the optimum pH for Cu(II) adsorption was 5. Equilibrium data were described using a Langmuir isotherm model. The Langmuir model maximum Cu(II) adsorption capacity (q m) increased with the algal dose in the following order: IMS 100 (1.710 mg g(-1)) > IMS 70 (1.548 mg g(-1)) > IMS 14 (1.282 mg g(-1)). The pseudo-second-order equation fitted the kinetics data well, and the value of the second-order rate constant increased with increasing algal dose. Gibbs free energies (ΔG°) were negative within the temperature range studied, which indicates that the adsorption process was spontaneous. The negative value of enthalpy (ΔH°) again indicates the exothermic nature of the adsorption process. In addition, SEM-energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS) analyses of the IMS surface reveal that the algal biomass on IMS is the main site for Cu(II) binding. This study shows that immobilized microalgae using silica, a synthesized biosorbent, can be used as a cost-effective sorbent for Cu(II) removal from the aqueous phase.

Molecular imprinting science and technology: a survey of the literature for the years 2004-2011

Herein, we present a survey of the literature covering the development of molecular imprinting science and technology over the years 2004-2011. In total, 3779 references to the original papers, reviews, edited volumes and monographs from this period are included, along with recently identified uncited materials from prior to 2004, which were omitted in the first instalment of this series covering the years 1930-2003. In the presentation of the assembled references, a section presenting reviews and monographs covering the area is followed by sections describing fundamental aspects of molecular imprinting including the development of novel polymer formats. Thereafter, literature describing efforts to apply these polymeric materials to a range of application areas is presented. Current trends and areas of rapid development are discussed.

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.

One-step patterning of hybrid xerogel materials for the fabrication of disposable solid-state light emitters

The one-step room-temperature micropatterning of a fluorophore-doped xerogel material on silicon oxide substrates is reported. The organo-alkoxysilane precursors and organic fluorescent dyes, as well as the polymerization experimental conditions, were tailored in order to obtain a highly homogeneous transparent material suitable for photonic applications. A thorough structural characterization was carried out by Fourier transform infrared (FT-IR) spectroscopy, (29)Si nuclear magnetic resonance ((29)Si NMR), thermogravimetric analysis (TGA), N(2) adsorption Brunauer-Emmett-Teller (BET) porosimetry, and confocal microscopy. These studies revealed a stable nonporous highly cross-linked polymer network containing evenly dispersed fluorescent molecules. Xerogel microstructures having thicknesses between 4 and 80 μm and height-to-width ratios between 0.04 and 4, as well as showing different geometries, from well arrays to waveguides, were patterned in a single step by micromolding in capillaries (MIMIC) soft lithographic technique. The reliability of the replication process was tested by bright-field optical microscopy and scanning electron microscopy (SEM) that show the close fidelity of the microstructures to the applied mold. The optical performance of the developed material was demonstrated by fabricating waveguides and evaluating their corresponding spectral response, obtaining absorption bands, at the expected excitation wavelengths of the corresponding fluorescent dyes and gain due to photonic re-emission (fluorescence) at their corresponding dye emission wavelengths. The hybrid xerogel material and the application of the simple fabrication technology presented herein can be directly applied to the development of cost-effective photonic components, as could be light emitters, to be readily integrated in single-use lab-on-chip devices and other polymeric microsystems.

Micro-algal biosensors

Fighting against water pollution requires the ability to detect pollutants for example herbicides or heavy metals. Micro-algae that live in marine and fresh water offer a versatile solution for the construction of novel biosensors. These photosynthetic microorganisms are very sensitive to changes in their environment, enabling the detection of traces of pollutants. Three groups of micro-algae are described in this paper: chlorophyta, cyanobacteria, and diatoms.