Release of Gold Nanoparticles from Phytomined Biomass by Enzymatic Digestion

Aaron T. Marshall1, Richard G. Haverkamp1, Clive E. Davies1, Jason G. Parsons2, Jorge L. Gardea-Torresdey2, and Dmitri Van Agterveld3. (1) Institute of Technology and Engineering, Massey University, Riddet Building, Riddet Road, Palmerston North, New Zealand, (2) Environmental Science and Engineering PhD Program and Department of Chemistry, The University of Texas at El Paso, 500 West University Avenue, El Paso, TX 79968-0513, (3) Department of Chemicals Analytics and Physics, Microstructure Analysis and Atomic Spectrometry, Akzo Nobel Research and Technology Chemicals, P O Box 9300 6800 SB, Arnhem, Netherlands

Gold nanoparticles are produced in some plants when soluble gold is present in the growth medium nutrients. Release and recovery of this gold by pyrolysis can sinter the particles, and enzymatic digestion is proposed as an alternative. Brassica juncea grown on soil containing low levels of gold, copper and silver (2248 mg Au kg-1, 4445 mg Cu kg-1 and 031 mg Ag kg-1 respectively) contained gold at weight concentrations circa 1000 ppm dry matter. 55-60 wt% of the dried plant matter was solubilised by enzymatic digestion, but 50-60% of the gold initially present was lost to solution during the digestion. XANES analysis shows that gold is present in the plant in approximately equal quantities in the metallic (Au0) and oxidized (Au+1) states. The gold lost during digestion is thought to be gold present in the plant in a soluble form (Au+1).