Design of Stable and Powerful Nanobiocatalysts, Based on Enzyme Laccase Immobilized on Self-Assembled 3D Graphene/Polymer Composite Hydrogels.

Graphene-based materials appear as a suitable answer to the demand for novel nanostructured materials for effective nanobiocatalytic systems design. In this work, a design of stable and efficient nanobiocatalysts made of enzyme laccase immobilized on composite hydrogels [reduced graphene oxide (rGO)/polymer] is presented. The composite hydrogel supports were synthesized by self-assembly of graphene oxide nanoplatelets in the frame of a polymer latex matrix, where the polymer nanoparticles were adsorbed onto the GO surface, creating hybrid nanoplatelets. These hybrids self-assembled when ascorbic acid was added as a GO reducing agent and formed three-dimensional porous structures, greatly swollen with water, e.g., the composite hydrogels. The hydrogels were used as a support for covalent immobilization of the laccase. The performance of the nanobiocatalysts was tested in the oxidative degradation of the recalcitrant synthetic dye Remazol Brilliant Blue R in aqueous solutions. The biocatalysts showed strong dye discoloration ability and high stability as they preserved their catalytic action in four successive batches of dye degradation. The presented biocatalysts offer possibilities for overcoming the main disadvantages of the enzyme catalysts (fragile nature, high cost, and high loading of the enzyme), which would lead to a step forward toward their industrial application.

Interaction of poly(N-isopropylacrylamide) (pNIPAM) based nanoparticles and their linear polymer precursor with phospholipid membrane models.

Poly(N-isopropylacrylamide) (pNIPAM) is a thermoresponsive polymer which has promising applications in nanomedicine for drug delivery. The cross-linking of pNIPAM based copolymer using the chain collapse method leads to the synthesis of pNIPAM based polymer nanoparticles. This study looks at the interaction of pNIPAM polymers and pNIPAM nanoparticles with biomembrane models of, (i) a dioleoyl phosphatidylcholine (DOPC) monolayer on a mercury (Hg) electrode and (ii) DOPC and dimyristoyl phosphatidylcholine (DMPC) vesicles. The following techniques were used to follow the interactions: Dynamic light scattering (DLS), differential scanning calorimetry (DSC), rapid cyclic voltammetry (RCV) and electrochemical impedance spectroscopy (EIS). Results showed that the polymers interacted more extensively than the nanoparticles with the phospholipid. The interaction of the polymer was more rapid and led to a polymer-phospholipid conjugate whereas the nanoparticle adsorbed on the phospholipid monolayer surface and penetrated the monolayer at longer contact times. The association of the linear polymer with the phospholipid can be related to the larger molecular area available with the pendant -Cl groups and the inherent polymeric flexibility compared to the nanoparticle structure. The apparent dissociation constant for nanoparticles-DOPC complex was K(d,app)=1.67 × 10(-5)±1.2 × 10(-6) mol dm(-3). The apparent kinetic constant of nanoparticle penetration through the DOPC monolayer was k(2,app)=1.054 × 10(-2)±9.1 × 10(-4) s(-1). It can be concluded therefore that the pNIPAM nanoparticle because of its lower affinity for phospholipids is more appropriate for medical applications.

Electronic anabolic steroid recognition with carbon nanotube field-effect transistors.

A proof of concept of the electronic detection of two anabolic steroids, stanozolol (Stz) and methylboldenone (MB), was carried out using two specific antibodies and arrays of carbon nanotube field-effect transistors (CNTFETs). Antibodies specific for Stz and MB were prepared and immobilized on the carbon nanotubes (CNTs) using two different approaches: direct noncovalent bonding of antibodies to the devices and bonding the antibodies covalently to a polymer previously attached to the CNTFETs. The results indicated that CNTFETs bonded to specific antibodies covalently or noncovalently are able to detect the presence of steroids. Statistically significant changes in the threshold voltage and drain current were registered in the transistors, allowing the steroids to be recognized. On the other hand, it was determined that the specific antibodies do not detect other steroids other than Stz and MB, such as nandrolone (ND) because, in this case, statistically significant changes in the transistors were not detected. The polymer prevents the aggregation of antibodies on the electrodes and decreases the transistor hysteresis. Nevertheless, it is not able to avoid the nonspecific adsorption of streptavidin, meaning that nonspecific adsorption on CNTs remains a problem and that this methodology is only useful for purified samples. Regarding the detection mechanism, in addition to charge transfer, Schottky barrier, SB, modification, and scattering potential reported by other authors, an electron/hole trapping mechanism leading to hysteresis modification has been determined. The presence of polymer seems to hinder the modulation of the electrode-CNT contact.

Label-free DNA biosensors based on functionalized carbon nanotube field effect transistors.

A carbon nanotube transistor array was used to detect DNA hybridization. A new approach to ensure specific adsorption of DNA to the nanotubes was developed. The polymer poly (methylmethacrylate(0.6)-co-poly(ethyleneglycol)methacrylate(0.15)-co-N-succinimidyl methacrylate(0.25)) was synthesized and bonded noncovalently to the nanotube. Aminated single-strand DNA was then attached covalently to the polymer. After hybridization, statistically significant changes were observed in key transistor parameters. Hybridized DNA traps both electrons and holes, possibly caused by the charge-trapping nature of the base pairs.