The effect of droplet dynamics on the kinetics of the horseradish peroxidase catalysed reaction in reverse micelles

Versatility of Reverse Micelles: From Biomimetic Models to Nano (Bio)Sensor Design

This paper presents an overview of the principal structural and dynamics characteristics of reverse micelles (RMs) in order to highlight their structural flexibility and versatility, along with the possibility to modulate their parameters in a controlled manner. The multifunctionality in a large range of different scientific fields is exemplified in two distinct directions: a theoretical model for mimicry of the biological microenvironment and practical application in the field of nanotechnology and nano-based sensors. RMs represent a convenient experimental approach that limits the drawbacks of the conventionally biological studies in vitro, while the particular structure confers them the status of simplified mimics of cells by reproducing a complex supramolecular organization in an artificial system. The biological relevance of RMs is discussed in some particular cases referring to confinement and a crowded environment, as well as the molecular dynamics of water and a cell membrane structure. The use of RMs in a range of applications seems to be more promising due to their structural and compositional flexibility, high efficiency, and selectivity. Advances in nanotechnology are based on developing new methods of nanomaterial synthesis and deposition. This review highlights the advantages of using RMs in the synthesis of nanoparticles with specific properties and in nano (bio)sensor design.

Formulation and Structural Study of a Biocompatible Water-in-Oil Microemulsion as an Appropriate Enzyme Carrier: The Model Case of Horseradish Peroxidase

A novel biocompatible water-in-oil microemulsion was developed using nonionic surfactants and was investigated as a potential enzyme delivery system for pharmaceutical applications. The system was composed of isopropyl myristate/polysorbate 80 (Tween 80)/distilled monoglycerides/water/propylene glycol (PG), had a low total surfactant concentration (8.3% w/w), and was able to incorporate approximately 3% w/w aqueous phase containing horseradish peroxidase (HRP). Structural and activity aspects of the system were studied using a variety of techniques such as dynamic light scattering (DLS), electron paramagnetic resonance (EPR), and dynamic interfacial tension. The apparent hydrodynamic diameter of the empty droplets was calculated at about 37 nm. Different enzyme concentrations, ranging from 0.01 to 1.39 μM, were used for both DLS and EPR studies to effectively determine the localization of the macromolecule in the microemulsion. According to the results, for high enzyme concentrations, a participation of HRP in the surfactant monolayer of the microemulsion is evident. The number of reverse micelles in the microemulsion was defined by a theoretical model and was used to clarify how the enzyme concentration affects the number of empty and loaded reverse micelles. To assure that the system allows the enzyme to retain its catalytic activity, an oxidative reaction catalyzed by HRP was successfully carried out with the use of the model substrate 2,2'-azino-bis[3-ethylbenzothiazoline-6-sulfonic acid]. The influence of several parameters such as temperature, pH, and PG concentration was examined to optimize the reaction conditions, and a kinetic study was conducted revealing an ordered-Bi-Bi mechanism. Values of all kinetic parameters were determined. The release of the encapsulated enzyme was studied using an adequate receiver phase, revealing the effectiveness of the proposed microemulsion not only as a microreactor but also as a carrier for therapeutic biomolecules.

Cell-free Protein Synthesis through Solubilisate Exchange in Water/Oil Emulsion Compartments

This work is aimed at finding conditions under which synthetic compartments used as cell models can fuse with each other and allow reagents contained in the different compartments to react. This goal seems to be best achieved by the use of water in oil emulsions (w/o) with dimensions in the range of 30-60 microm. In particular, cell-free EGFP (enhanced green fluorescent protein) synthesis takes place in Tween 80/Span 80 w/o emulsions, and the extent of the reaction can be monitored directly by fluorescence. The medium is mineral oil, containing 0.5 % v/v aqueous solution. Different premixing configurations of the components (plasmid, amino acids, E. Coli extract) are used and compared. The in vitro synthesis of EGFP in emulsion droplets proceeds for 1 h, and the yield is 7.5 ng microL(-1) protein. EGFP synthesis in aqueous solution takes place for at least 5 h. The yield is 10.5 ng microL(-1) protein after 1 h and 15.8 ng microL(-1) protein after 5 h. The results with the w/o emulsions show that solubilisate exchange takes place among the different water droplets, but it is not possible to demonstrate clearly that a true fusion takes place.