Synthesis of silver nanoparticles: chemical, physical and biological methods.

Silver nanoparticles (NPs) have been the subjects of researchers because of their unique properties (e.g., size and shape depending optical, antimicrobial, and electrical properties). A variety of preparation techniques have been reported for the synthesis of silver NPs; notable examples include, laser ablation, gamma irradiation, electron irradiation, chemical reduction, photochemical methods, microwave processing, and biological synthetic methods. This review presents an overview of silver nanoparticle preparation by physical, chemical, and biological synthesis. The aim of this review article is, therefore, to reflect on the current state and future prospects, especially the potentials and limitations of the above mentioned techniques for industries.

Immobilization of penicillin G acylase using permeabilized Escherichia coli whole cells within chitosan beads.

Entrapment of permeabilized whole cells within a matrix is a common method for immobilization. Chitosan possesses distinct chemical and biological properties, which make it a suitable matrix for entrapment and immobilization of penicillin G acylase (PGA). In the first step, Escherichia coli (ATCC 11105) cells were permeabilized using N-cetyl-N,N,N-trimethyl ammonium bromide (CTAB) (0.1% w/v, 45 min, 45 rpm) which then immobilized using glutaraldehyde (5% w/v) as cross-linker and chitosan (3% w/v) as the matrix. These conditions were established after preliminary trials with CTAB and glutaraldehyde concentrations in the range of 0.05-0.25% w/v and 1-9% v/v, respectively. The hydrolytic activity was assayed using Ehrlich reagent. Permeabilization of cells caused 9% increase in Penicillin G Acylase (PGA) conversion after 15 min compared to the intact cells. Although, immobilization on chitosan decreased the conversion compared to un-immobilized treated cells (13%), the new biocatalyst showed acceptable operational stability, maintaining more than 90% of the initial activity after 20 cycles. Optimum conditions for immobilization of E. coli cells were: CTAB 0.1% w/v and glutaraldehyde 5% v/v. A new combination method was successfully developed and optimized for immobilization of treated whole cells on chitosan matrix.