Fractal dimension analysis of swarms of gold nano/micro particles produced by wild Rhizobium cultures using a novel slide based system

Abstract

There is a lot of interest in autonomous movement and collective behavior of synthetic nanomaterials which have important applications in nanomedicine, nanobiotechnology and nanosensors. Present work using viable cultures and cell free extracts of Rhizobium sp. to produce and analyze swarms of monodisperse Au Nanoparticles (Au NPs) and polydisperse Au microparticles (Au MPs) was inspired by previously reported work on chemically triggered swarming of commercially available Au MPs. We developed a simple, glass slide based technique for rapid production, microscopic visualization, morphological analysis, study of swarming behavior and monitoring of effects of heat on Au NPs and Au MPs forms and assemblages. We designed cell based and cell free microbial system such as Rhizobium sp. to test the hypothesis that unidentified proteinaceous factors could be involved in producing simple monodisperse and complex polydisperse geometric forms of Au NPs and Au MPs. We used pure and wild type Rhizobium cell suspensions prepared from surface sterilized root nodules of Mimosa pudica. Cell free extracts from wild type and pure cultures were prepared by warming cell suspensions for 15, 30, and 45 sec. Cultures and extracts were separately mixed with HAuCl sub(4) in equal proportions in each treatment on slides and monitored microscopically. For studying effect of heat slides were warmed for 15, 30, 45 seconds. Mixed, dense swarms of monodisperse Au NPs were obtained with polydisperse Au MPs using wild type and pure cultures as well as cell free extracts. Heat treatment yielded interesting forms and complex assemblages exhibiting fractal properties. We postulate that Rhizobium sp. specific unidentified cell bound heat responsive proteins may trigger monodisperse Au NPs swarms and simple and complex assemblages or acidic conditions may release amino acids from protein hydrolysis which may act as capping and linking agents. Some of these assemblages or acidic conditions may release amino acids from protein hydrolysis which may act as capping and linking agents. Some of these assemblages such as open and closed rings, interlocked rings are unique. Using our simple slide based technique a lot of scope exists for applying a combination of microbial cell free extracts and timed heat treatment to obtain defined monodisperse GNP swarms. This study showed the potential of fractal dimension analysis to study biotechnologically useful forms of Au NPs and polydisperse Au MPs.