RESEARCH ARTICLE Copyright © 2008 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 8, 3565–3569, 2008 Hydrazine Based Facile Synthesis and Ordered Assembly of Metal Nanoparticles (Au, Ag) on a Bacterial Surface Layer Protein Template Sarang S. Puranik 1 , Hrushikesh M. Joshi 2 , S. B. Ogale 2 * , and K. M. Paknikar 1 * 1 Centre for Nanobioscience, Agharkar Research Institute, Pune 411004, India 2 Physical and Materials Chemistry Division, National Chemical Laboratory, Pune 411008, India An efficient and facile procedure is developed for concurrent in situ synthesis and ordered assembly of metal nanoparticles on a periodic two dimensional protein array. The S-layer protein of Bacillus subtilis exhibiting uniform pore size is used as template. Synthesis of gold and silver nanoparticles anchoring on the pores of S-layer is achieved by chemical reduction of respective metal salt laden protein template. Transmission electron microscopy reveals formation of well ordered and separated gold and silver nanoparticles with an average diameter of 6 ± 1 nm and 4 ± 1 nm, respectively. The periodic arrangement of nanoparticles is dictated by the native structure of S-layer protein array as the nanoparticle locations are found to be correlated to the nanosized pores of the crystalline S-layer array. Keywords: Metal Nanoparticles, Synthesis, Bacteria. 1. INTRODUCTION In recent years, the bottom up approach which mimics inherent construction principles of biological systems is gaining importance for the fabrication of ordered nano- structures as compared to top down techniques such as electron beam lithography, ion beam lithography, X-ray lithography, etc. which are technically compli- cated, expensive and inefficient. Several interesting studies have been made to assemble nanomaterials using macro- molecular systems such as DNA, 1–4 diblock co-polymers, 5 surfactants, 6 carbon nanotubes, fullerenes, 7 8 etc. In these examples, interactions at molecular level or intrinsic material properties are used as driving force to assemble nanomaterials. In contrast to the use of conventional chem- ical routes for the synthesis and assembly of nanoparti- cles, exploiting the natural tendency of biomolecules such as proteins, DNA to yield perfect self-assemblies through molecular specificities clearly offers novel and effective alternatives for nanofabrication. Such molecules can pro- vide interactive surface templates for inorganic/organic molecular functionalizations and in situ synthesis. Bacterial S-layer lattices exhibit pores of identical size (2–8 nm), morphology, and uniform thickness (5–35 nm). The functional groups on the surface and pores are aligned * Authors to whom correspondence should be addressed. in well-defined position and orientation, and are accessi- ble for binding to functional molecules in a very precise fashion. Most importantly, the isolated S-layer subunits can self-assemble and are capable of recrystallizing into monolayers onto solid supports, at the air/water interface, on Langmuir lipid films and on liposomes. As shown by Mann, Sleytr and coworkers as well as others, 9–17 these unique properties displayed on a nanometer scale make S-layer lattices ideal structures for functionalization of sur- faces and interfaces for fabricating nanostructures required for the development of new generation optical and elec- tronic devices, and for the formation of metal nanocluster arrays such as gold and silver for nanoelectronic digital circuits. Mann et al. assembled two dimensional arrays of CdS nanoparticles on the S-layer protein by exposing H 2 S gas to Cd ions anchored on S-layer protein. 9 Sleytr and coworkers reported the synthesis of gold nanoclus- ters of ∼4 nm diameter using S-layer of B. sphaericus CCM 2177. 10 The reduction of gold was also achieved by treating the gold-exposed S-layer array to H 2 S for two days. Dieluweit et al. and Mertig et al. 11 12 used electron beam for the reduction of the metal deposited on S-layer. Merroun et al. used H 2 gas as the reducing agent to synthesize gold nanoparticles in the presence of S-layer protein of B. sphaericus JG-A 12. 13 Hall et al. used presynthesized gold nanoparticles to form assemblies on J. Nanosci. Nanotechnol. 2008, Vol. 8, No. 7 1533-4880/2008/8/3565/005 doi:10.1166/jnn.2008.135 3565