PUBLISHED VERSION

Geochemical exploration for gold (Au) is becoming increasingly important to the mining industry. Current processes for Au analyses require sampling materials to be taken from often remote localities. Samples are then transported to a laboratory equipped with suitable analytical facilities, such as Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) or Instrumental Neutron Activation Analysis (INAA). Determining the concentration of Au in samples may take several weeks, leading to long delays in exploration campaigns. Hence, a method for the on-site analysis of Au, such as a biosensor, will greatly benefit the exploration industry. The golTSB genes from Salmonella enterica serovar typhimurium are selectively induced by Au(I/III)-complexes. In the present study, the golTSB operon with a reporter gene, lacZ, was introduced into Escherichia coli. The induction of golTSB::lacZ with Au(I/III)-complexes was tested using a colorimetric b-galactosidase and an electrochemical assay. Measurements of the b-galactosidase activity for concentrations of both Au(I)and Au(III)-complexes ranging from 0.1 to 5 mM (equivalent to 20 to 1000 ng g or parts-per-billion (ppb)) were accurately quantified. When testing the ability of the biosensor to detect Au(I/III)-complexes(aq) in the presence of other metal ions (Ag(I), Cu(II), Fe(III), Ni(II), Co(II), Zn, As(III), Pb(II), Sb(III) or Bi(III)), cross-reactivity was observed, i.e. the amount of Au measured was either underor over-estimated. To assess if the biosensor would work with natural samples, soils with different physiochemical properties were spiked with Au-complexes. Subsequently, a selective extraction using 1 M thiosulfate was applied to extract the Au. The results showed that Au could be measured in these extracts with the same accuracy as ICP-MS (P,0.05). This demonstrates that by combining selective extraction with the biosensor system the concentration of Au can be accurately measured, down to a quantification limit of 20 ppb (0.1 mM) and a detection limit of 2 ppb (0.01 mM). Citation: Zammit CM, Quaranta D, Gibson S, Zaitouna AJ, Ta C, et al. (2013) A Whole-Cell Biosensor for the Detection of Gold. PLoS ONE 8(8): e69292. doi:10.1371/ journal.pone. 0069292 Editor: Vipul Bansal, RMIT University, Australia Received July 14, 2011; Accepted June 12, 2013; Published August 9, 2013 Copyright: 2013 Zammit et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This study was funded via an Australian Research Council (ARC) Linkage Grant and the following partners Commonwealth Scientific and Industrial Research Organisation, The University of Adelaide, Newmont Exploration Proprietary Limited and Barrick Gold of Australia Limited, the Institute for Mineral and Energy Resources and the Centre for Tectonics, Resources and Exploration. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have read the journal’s policy and have the following conflict: Newmont Exploration Proprietary Limited and Barrick Gold of Australia Limited helped fund this study. This does not alter the authors’ adherence to all of the PLOS ONE policies on sharing data and materials. * E-mail: carla.zammit@adelaide.edu. au (CMZ); Frank.Reith@csiro.au (FR)