Antibacterial Effects of Ag, Au and Bimetallic (Ag-Au) Nanoparticles Synthesized from Red Algae

Abstract

Recently the utilization of prokaryotic cells (such as bacteria, algae) and plants have emerged as novel methods for the synthesis of nanoparticles intracellularly. Therefore the applications on living organisms have recently attracted the attention of biologists towards nanobiotechnology. In the present study, Silver, Gold and bimetallic alloy Ag-Au nanoparticles were synthesized from marine red alga,Gracilaria sp.,of Gulf of Mannar with different molar concentrations of 100%Ag, 100% Au and Ag:Au (1:1, 1:3 and 3:1). The reduction of Ag, Au and Ag:Au NPs was confirmed by change of colour (i.e. from transparent to dark brown for silver NPs, to ruby red for gold NPs and pale pink for bimetallic NPs) as well as by peak absorption spectra. The absorption peak of theGracilaria sp.,for 100% Ag occurred at 419nm, for 100% Au at 536nm, for Ag: Au (1:1) concentrations at 504 nm for Ag: Au (1:3) at 526 nm and for Ag: Au (3:1) at 501nm. The size of Ag, Au and bimetallic Ag-Au NPs was measured by SEM analysis, proved that the synthesized nanoparticles were colloidal in nature. The bimetallic nanoparticles exhibited good antibacterial activity against Gram positive bacteriaStaphylococcus aureusand Gram negative bacteriaKlebsiella pneumoniae. The above results revealed thatSalmonella typhiiandEscherichia colihave no activity. However, bimetallic NPs of 1:3 concentration showed zones of inhibition against the pathogenic bacteria such asStaphylococcus aureusandKlebsiella pneumoniaerather than Ag NPs and Au NPs. This process of the nanoparticles production is eco-friendly as it is free from any solvent or toxic chemicals, and is also easily amenable for large-scale production.