Synthesis of Alginate Nanogels with Polyvalent 3D Transition Metal Cations: Applications in Urease Immobilization.

Biocompatible nanogels are highly in demand and have the potential to be used in various applications, e.g., for the encapsulation of sensitive biomacromolecules. In the present study, we have developed water-in-oil microemulsions of sodium alginate sol/hexane/Span 20 as a template for controlled synthesis of alginate nanogels, cross-linked with 3d transition metal cations (Mn2+, Fe3+, and Co2+). The results suggest that the stable template of 110 nm dimensions can be obtained by microemulsion technique using Span 20 at concentrations of 10mM and above, showing a zeta potential of -57.3 mV. A comparison of the effects of the cross-links on the morphology, surface charge, protein (urease enzyme) encapsulation properties, and stability of the resulting nanogels were studied. Alginate nanogels, cross-linked with Mn2+, Fe3+, or Co2+ did not show any gradation in the hydrodynamic diameter. The shape of alginate nanogels, cross-linked with Mn2+ or Co2+, were spherical; whereas, nanogels cross-linked with Fe3+ (Fe-alginate) were non-spherical and rice-shaped. The zeta potential, enzyme loading efficiency, and enzyme activity of Fe-alginate was the highest among all the nanogels studied. It was found that the morphology of particles influenced the percent immobilization, loading capacity, and loading efficiency of encapsulated enzymes. These particles are promising candidates for biosensing and efficient drug delivery due to their relatively high loading capacity, biocompatibility, easy fabrication, and easy handling.

Super protective anti-bacterial coating development with silica-titania nano core-shells.

In the present study, we have developed an anti-bacterial as well as mechanically-strengthened super protective coating material, which can be used as a marine antifouling paint. In this research, silica, titania and silica-titania core-shell nanoparticles were individually prepared via sol-gel and peptization processes. The idea behind the synthesis of core-shell nanoparticles was to utilize the mechanical strength of silica and the antimicrobial property of TiO2 together. These nanoparticles were characterized via dynamic light scattering, UV-Visible spectroscopy, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Coating formulations were developed with two types of model binders, i.e., solvent-based polyurethane and water-based poly-acrylic, containing all nanoparticles individually at various concentrations for a better comparative study. These coating formulations were applied onto mild steel for anti-bacterial testing that was performed against Escherichia coli and Bacillus. The nanoparticle concentration was varied from 1% (wt) to 6% (wt). The best anti-bacterial result was obtained with 4% (wt) of silica-titania core-shell nanoparticles prepared via the peptization process among all the nanoparticles. The scratch testing was performed successfully using an Erichsen scratch tester; the formulated PU coating passed up-to 20 N load with good adhesion, impact resistance, flexibility and has shown satisfactory anti-corrosion performance.

Biopolymer matrix for nano-encapsulation of urease - A model protein and its application in urea detection.

Alginate microparticles and nanoparticles crosslinked with Ca+2 ions are frequently employed in biomedical applications. Here we use microemulsion polymerization to prepare alginate nanoparticles (nanogels) using different crosslinking ions (Ca+2, Sr+2, Ba+2) to encapsulate a model protein, urease enzyme (jackbeans). With alginate concentrations of 0.2wt% in the aqueous phase, emulsion droplets showed good stability and narrow, monomodal distributions with radii ∼65±10nm. The size of the nanogel varies with the crosslinking cation and its affinity for the mannuronate and guluronate units in the linear alginate chain. The nanogels were further characterized using dynamic light scattering, scanning electron microscopy, energy dispersive X-ray spectrometry and zeta potential. This work demonstrates the potential application of Ba-alginate as an alternative matrix for nano-encapsulation of proteins and its use for biomedical applications.

A comparative study of immobilization techniques for urease on glass-pH-electrode and its application in urea detection in blood serum.

Different techniques have been used (physical adsorption, physically entrapped sandwich and microencapsulation) for the immobilization of urease enzyme in tetramethylorthosilicate (TMOS) derived sol-gel matrix on the sensing surface of glass-pH-electrode. No significant leaching of enzyme occurs from the microencapsulated and physically entrapped enzyme sandwich films. Potentiometric techniques have been used for the estimation of urea concentration in each instance. Various parameters of biosensor performance have been studied which indicates that microencapsulation technique is a better method of enzyme immobilization in sol-gel films derived from TMOS. The advantage of microencapsulated biosensor over others include higher sensitivity (dpH/dp(C)=2.4), lower detection limit of 52 microg mL(-1), larger linear range (0.01-30 mM) of urea determination and reasonably long-term stability of about 25 days with 80% response signal.