Biochemical Engineering Journal 55 (2011) 1–6 Contents lists available at ScienceDirect Biochemical Engineering Journal journal homepage: www.elsevier.com/locate/bej Time dependent formation of gold nanoparticles in yeast cells: A comparative study Kamalika Sen a,∗ , P. Sinha b , Susanta Lahiri c a Department of Chemistry, University of Calcutta, 92 APC Road, Kolkata 700009, India b Department of Biochemistry, Bose Institute, Centenary Campus, P-1/12 CIT Scheme VII-M, Kolkata 700 054, India c Chemical Sciences Division, Saha Institute of Nuclear Chemistry, 1/AF Bidhannagar, Kolkata 700 064, India article info Article history: Received 15 June 2010 Received in revised form 12 February 2011 Accepted 19 February 2011 Available online 23 March 2011 Keywords: Saccharomyces cerevisiae TEM Gold nano particles H 198 AuCl4 Thin sectioning Uptake kinetics abstract Two different strains of yeast, Saccharomyces cerevisiae, AP22 and CCFY-100 were studied for bioaccumu- lation of gold in the form of H 198 AuCl 4 . Thin sectioning and subsequent study by transmission electron microscopy (TEM) reveals that Au 3+ was in situ reduced to Au(0) and nano sized gold particles were formed inside the cell. Very low dose -energy being responsible for reduction of cationic gold in the polymeric cytoplasm matrix. The formation and entry of gold nanoparticles in the yeast cells were stud- ied as a function of time at certain intervals starting from 15 min to 72 h. The gold nanoparticles gradually moved inward as a function of time from cell wall to cytoplasm to nucleus and finally accumulated in the nucleolus of the cell. TEM image of budding yeast shows that gold nanoparticles are not transferred to the new generation yeast cells. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Biological substrates have shown promising abilities for interac- tion with metal ions [1–3]. Proteins and carbohydrates of cell wall provide good sites for metal binding [4]. They appear to be the safer alternatives towards designing greener technology for the future [5]. Among various eukaryotic organisms yeasts play an important role as a model of eukaryotic cells for biochemical and physiochem- ical experiments. For example, the effects of some heavy metals on the growth of some soil-yeasts were studied [6]. As a useful means of bioremediation of environmental chromium contamina- tion, yeasts were used to treat Cr containing effluents in order to remove toxic compounds from waters and soils [7]. Earlier, we have also reported extraction of 152 Eu, a long-lived fission product, by yeast cells, Saccharomyces [8]. The dry waste biomass of powder of Saccharomyces cerevisiae obtained from beer fermentation was studied for Au 3+ biosorption [9]. Synthesis of gold nanoparticles from different biological agents like bacteria, fungi and plant extracts have been reported earlier, which have potential applications in hyperthermia in cancer cells [10]. Recently, the use of precious metal gold in nanotechnology has increased in leaps and bounds due to its wide application in elec- tronics, chemistry, and engineering owing to their specific optical ∗ Corresponding author. E-mail addresses: kschem@caluniv.ac.in, kamalchem.roy@gmail.com (K. Sen). and electrical properties. Moreover, gold nanoparticles are promis- ing in the field of clinical sciences, especially for in vivo application. The intracellular synthesis of gold nanoparticles of various mor- phologies and sizes in two fungal cultures, V. luteoalbum and Isolate 6-3 has been documented earlier [11]. The size of nanoparticles can be manipulated by controlling parameters such as pH, tem- perature, gold concentration and exposure time to gold solution. On the other hand, the effects of ionic gold on S. cerevisiae, was determined by long-term and short-term interactions [12]. The addition of low concentrations of gold as tetrachloroaurate salt to growth medium resulted in the formation of a dispersed phase over 10–12 h incubation. Transmission electron microscopy revealed no differences in ultrastructure. No gold deposits were observed in transmission electron micrographs of cells grown in presence of gold, in contrast to numerous gold particles located outside the cell. From our earlier work on synthesis of gold nanoparticles, we have observed that minuscule amount of in situ radioactivity from 198 Au radioisotope (T 1/2 = 2.69 d) can induce radiolysis in poly- mer matrix (polyethylene glycol, PEG) and in turn reduce Au(III) to Au(0) [13]. Similarly, minute amount of in situ radioactivity from 198 Au radioisotope is also capable of synthesizing Au–Pd bimetallic nanoparticles in a PEG matrix [14]. Biological cells are composed of various polymeric substances, e.g., cell wall of yeast is made of 30–60% polysaccharides (beta-glucan and mannan sugar poly- mers), 15–30% proteins, 5–20% lipids and a small amount of chitin [15]. Considering this fact, we thought that such media may also 1369-703X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.bej.2011.02.014