• Lloyd, Jonathan R.
• Haigh, Sj
• Collins, Richard
• Laurie, Helen
• Prestat, Eric
• Lewis, Edward

Abstract

PdAu nanocrystals were synthesised by Geobacter sulfurreducens, a dissimilatory metalreducing bacterium, and the resulting bimetallic nanocrystal decorated microbes were imaged using a range of advanced electron microscopy techniques. Specifically we report the first example of elemental mapping of fully hydrated biological nanostructures using scanning transmission electron microscope (STEM) energy dispersive X-ray (EDX) spectrum imaging within an environmental liquid-cell. We combine these results with cryo-TEM and ex situ STEM imaging and EDX analysis with the aim of better understanding microbial synthesis of bimetallic nanoparticles. We demonstrate that although Au and Pd are colocalised across the cells, the population of nanoparticles produced is bimodal, containing ultra-small alloyed nanocrystals with diameters <3nm and significantly larger core-shell structures (> 200nm in diameter) which show higher Pd contents and exhibited a Pd enriched rich shell only a few nanometres thick. The application of high-resolution imaging techniques described here offers the potential to visualise the microbe-metal interface during the bioproduction of a range of functional materials by microbial “green” synthesis routes, and also key interfaces underpinning globally relevant environmental processes (e.g. metal cycling).

Topics

• nanoparticle
• impedance spectroscopy
• transmission electron microscopy
• Energy-dispersive X-ray spectroscopy