Nanocomposite-based dual enzyme system for broad-spectrum scavenging of reactive oxygen species.

A broad-spectrum reactive oxygen species (ROS)-scavenging hybrid material (CASCADE) was developed by sequential adsorption of heparin (HEP) and poly(L-lysine) (PLL) polyelectrolytes together with superoxide dismutase (SOD) and horseradish peroxidase (HRP) antioxidant enzymes on layered double hydroxide (LDH) nanoclay support. The synthetic conditions were optimized so that CASCADE possessed remarkable structural (no enzyme leakage) and colloidal (excellent resistance against salt-induced aggregation) stability. The obtained composite was active in decomposition of both superoxide radical anions and hydrogen peroxide in biochemical assays revealing that the strong electrostatic interaction with the functionalized support led to high enzyme loadings, nevertheless, it did not interfere with the native enzyme conformation.

Co-immobilization of antioxidant enzymes on titania nanosheets for reduction of oxidative stress in colloid systems.

Immobilization of single antioxidant enzyme systems was frequently studied in the past, however, there is a lack of reliable reports on the co-immobilization of such enzymes. Here, an antioxidant enzyme cascade involving superoxide dismutase (SOD) and horseradish peroxidase (HRP) was successfully immobilized on titania nanosheets (TNS) by the sequential adsorption method using poly(diallyldimethylammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) polyelectrolyte building blocks. The development of the cascade system was based on a colloid approach, in which the charging and aggregation processes were optimized in each synthetic step.

Self-Assembly of Protamine Biomacromolecule on Halloysite Nanotubes for Immobilization of Superoxide Dismutase Enzyme.

An antioxidant material composed of halloysite nanotubes (HNTs), protamine sulfate polyelectrolyte (PSP), and superoxide dismutase (SOD) enzyme was prepared by self-assembly of the PSP and SOD biomacromolecules on the nanoparticulate support. The structural, colloidal and biocatalytic features were assessed. Adsorption of PSP on the oppositely charged HNT surface at appropriate loadings gave rise to charge neutralization and overcharging, which resulted in unstable and stable dispersions, respectively.

Layer-by-layer assembly of enzyme-loaded halloysite nanotubes for the fabrication of highly active coatings.

The development of sturdy enzyme-containing hydrophilic coatings is important for applications such as water purification or biological sensing. Here, we investigate the encapsulation of a model enzyme (beta-lactamase, BlaP) into aluminosilicate halloysite nanotubes (HNTs), and their subsequent use for the fabrication of enzymatic coatings by layer-by-layer (LbL) assembly. Highly stable suspensions of enzymatically-active halloysite nanotubes were obtained by alkaline treatment of HNTs, followed by enzyme adsorption into the lumen of the nanotubes and of poly(ethylene imine) (PEI) onto their outer surface.

Regulation of the Stability of Titania Nanosheet Dispersions with Oppositely and Like-Charged Polyelectrolytes.

Charging and aggregation processes of titania nanosheets (TNS) were extensively studied in the presence of oppositely charged or like-charged polyelectrolytes in aqueous dispersions. The surface charge of the TNS was systematically varied by the pH; therefore, positive nanosheets were obtained at pH 4 and negative ones at pH 10. Strong adsorption of poly(styrene sulfonate) (PSS) of high negative line charge density on the TNS was observed at pH 4, leading to charge neutralization and reversal of the original sign of charge of the nanosheets.

Highly stable enzyme-mimicking nanocomposite of antioxidant activity.

A highly stable nanocomposite of antioxidant activity was developed by immobilization of a superoxide dismutase-mimicking metal complex on copolymer-functionalized nanoclay. The layered double hydroxide (LDH) nanoclays were synthesized and surface modification was performed by adsorbing poly(vinylpyridine-b-methacrylic acid) (PVPMAA). The effect of the adsorption on the charging and aggregation properties was investigated and the copolymer dose was optimized to obtain stable LDH dispersions.

Horseradish peroxidase-nanoclay hybrid particles of high functional and colloidal stability.

Highly stable dispersions of enzyme-clay nanohybrids of excellent horseradish peroxidase activity were developed. Layered double hydroxide nanoclay was synthesized and functionalized with heparin polyelectrolyte to immobilize the horseradish peroxidase enzyme. The formation of a saturated heparin layer on the platelets led to charge inversion of the positively charged bare nanoclay and to highly stable aqueous dispersions.

Immobilization of Superoxide Dismutase on Polyelectrolyte-Functionalized Titania Nanosheets.

The superoxide dismutase (SOD) enzyme was successfully immobilized on titania nanosheets (TNS) functionalized with the poly(diallyldimethylammonium chloride) (PDADMAC) polyelectrolyte. The TNS-PDADMAC solid support was prepared by hydrothermal synthesis followed by self-assembled polyelectrolyte layer formation. It was found that SOD strongly adsorbed onto oppositely charged TNS-PDADMAC through electrostatic and hydrophobic interactions.

Influence of Protamine Functionalization on the Colloidal Stability of 1D and 2D Titanium Oxide Nanostructures.

The colloidal stability of titanium oxide nanosheets (TNS) and nanowires (TiONW) was studied in the presence of protamine (natural polyelectrolyte) in aqueous dispersions, where the nanostructures possessed negative net charge, and the protamine was positively charged. Regardless of their shape, similar charging and aggregation behaviors were observed for both TNS and TiONW. Electrophoretic experiments performed at different protamine loadings revealed that the adsorption of protamine led to charge neutralization and charge inversion depending on the polyelectrolyte dose applied.

Destabilization of Titania Nanosheet Suspensions by Inorganic Salts: Hofmeister Series and Schulze-Hardy Rule.

Ion specific effects on colloidal stability of titania nanosheets (TNS) were investigated in aqueous suspensions. The charge of the particles was varied by the pH of the solutions, therefore, the influence of mono- and multivalent anions on the charging and aggregation behavior could be studied when they were present either as counter or co-ions in the systems. The aggregation processes in the presence of inorganic salts were mainly driven by interparticle forces of electrostatic origin, however, chemical interactions between more complex ions and the surface led to additional attractive forces.

Design of latex-layered double hydroxide composites by tuning the aggregation in suspensions.

Colloidal stability of polymeric latex particles was studied in the presence of oppositely charged layered double hydroxide (LDH) platelets of different interlayer anions. Adsorption of the LDH particles led to charge neutralization and to overcharging of the latex at appropriate concentrations. Mixing stable colloidal suspensions of individual particles results in rapid aggregation once the LDH adsorption neutralizes the negative charges of the polymer spheres, while stable suspensions were observed at high and low LDH doses.

Tuning Colloidal Stability of Layered Double Hydroxides: From Monovalent Ions to Polyelectrolytes.

The growing number of applications of layered double hydroxide (LDH) colloids demands for detailed understanding of particle aggregation processes in such samples. Tuning the colloidal stability in aqueous suspensions is essential to design stable systems or to induce controlled aggregation of these elongated particles. In this review, recent progress in this field is summarized; in particular, the charging and aggregation of LDHs of various compositions and sizes in the presence of different aggregating agents are discussed.

Synthesis and formulation of functional bionanomaterials with superoxide dismutase activity.

Layered double hydroxide (LDH) nanoparticles were prepared and used as solid support for superoxide dismutase (SOD) enzymes. Structural features were studied by XRD, spectroscopic methods (IR, UV-Vis and fluorescence) and TEM, while colloidal stability of the obtained materials was investigated by electrophoresis and light scattering in aqueous dispersions. The SOD quantitatively adsorbed on the LDH by electrostatic and hydrophobic interactions and kept its structural integrity upon immobilization.