Silver Nanoparticles as a Glucose Oxidase Immobilization Matrix for Amperometric Glucose Biosensor Construction

Immobilization of β-galactosidase on tannic acid stabilized silver nanoparticles: A safer way towards its industrial application

In this study, β-galactosidase has been immobilized on tannic acid stabilized silver nanoparticles (AgNPs). Tannic acid is a phytochemical and it is advantageous to use it as a linker molecule for immobilization because of its antidiarrheal and antimicrobial properties, and very low toxicity. AgNPs with immobilized β-galactosidase were characterized for particle size and catalytic properties. The AgNPs consisted of almost monodispersed particles of average diameter of ∼20 nm. β-galactosidase immobilized on tannic acid stabilized AgNPs (83.6% Immobilization yield) exhibited good activity with a high enzyme to carrier ratio as compared to the previous reports. Immobilization did not affect the optimum pH (pH 4.5) of the enzyme, however it retained greater fraction of activity in both alkaline and acidic pH range. The immobilized enzyme exhibited greater fraction of activity at higher temperatures as compared to the soluble enzyme, and its optimum temperature increased by 5 °C. The immobilized enzyme retained almost 60% of its activity after 10th successive use. The immobilized enzyme hydrolyzed 258 and 474 μM lactose from 1% lactose and from milk lactose, respectively, whereas the soluble enzyme hydrolyzed 235 and 424 μM lactose from 1% lactose and from milk lactose, respectively. Excellent activity and stability of β-galactosidase immobilized on AgNPs provides a cost-effective industrial application of this enzyme. β-galactosidase immobilized on tannic acid stabilized AgNPs are free from toxicity hazards of the linker molecules. Hence, it may find constructive enzyme based applications in food technology.

Synthesis and characterization of cysteine functionalized silver nanoparticles for biomolecule immobilization

A facile method for the aqueous phase synthesis of cysteine-functionalized silver nanoparticles by potato extract has been reported in the present work. These functionalized nanoparticles were then used for the covalent immobilization of a biomolecule, alkaline phosphatase, on its surface through carbodiimide coupling. Different reaction parameters such as cysteine concentration, reducing agent concentration, temperature, pH and reaction time were varied during the nanoparticles' formation, and their effects on plasmon resonance were studied using Ultraviolet-visible spectroscopy. Fourier transform infrared spectroscopy was used to confirm the surface modification of silver nanoparticles by cysteine and the particle size analysis was done using particle size analyzer, which showed the average nanoparticles' size of 61 nm for bare silver nanoparticles and 201 nm for the enzyme-immobilized nanoparticles. The synthesized nanoparticles were found to be highly efficient for the covalent immobilization of alkaline phosphatase on its surface and retained 67% of its initial enzyme activity (9.44 U/mg), with 75% binding efficiency. The shelf life of the enzyme-nanoparticle bioconjugates was found to be 60 days, with a 12% loss in the initial enzyme activity. With a simple synthesis strategy, high immobilization efficiency and enhanced stability, these enzyme-coated nanoparticles have the potential for further integration into the biosensor technology.