Deposition of CTAB-Terminated Nanorods on Bacteria to Form Highly Conducting Hybrid Systems

Authors

Ravi F. SarafFollow
Catherine J. Murphy
Subrata Kundu
Anand Gole
Vikas BerryFollow

Date of this Version

September 2005

Comments

This Publication was orginally published by American Chemical Society on web 11/23/2005 (10.1021/ja056428l © 2005 American Chemical Society).

Abstract

Interaction of nanoparticles with biological systems ranging from biomolecules to biological cells is of importance for a range of applications, such as high-resolution biomedical imaging,1 gene sequencing for molecular diagnostics,2 and sensitive electronic devices.3 In this report, we demonstrate that positively charged cetyltrimethylammonium bromide (CTAB), which is a stabilizing agent used to synthesize different metal nanoshapes4-7 (such as rods, spheres, cubes, prisms, stars, and hexagons), is an effective nanoparticle coating for self-assembling an electrically percolating monolayer of different nanoshapes on gram-positive bacterium, such as Bacillus cereus. The versatility of CTAB is especially realized for deposition of nanorods, where we observe 4 orders of magnitude larger conductivity compared to that of nanospheres at 3 times smaller area coverage. For the deposition on a “physical surface”, the rods do not form electrically percolating channels.8 Formation of such a percolating-conducting network on bacterium is attributed to high adhesion that overcomes steric interaction (responsible for liquid-crystalline order (see Figure 1a)), leading to random orientation (see Figure 2a). Furthermore, the strong adhesion (evidenced by conformal deposition of a rod causing bending) lowers the contact resistance, leading to 104 increases in conductivity at 13.5% area coverage compared to spheres with 41% area coverage (see Figure 3). This high conductivity is achieved well below the percolation threshold for random structure at 45% area coverage in two dimensions.9 With only �10% of bacterium surface covered, the microorganism may remain alive for a time longer than that for >40% coverage systems with nanosphere deposition.10 While CTAB alone is toxic to cells, CTAB-coated nanoparticles are nontoxic.11 Electronic coupling between nanorod monolayers with microorganisms can open the possibility of novel hybrid devices utilizing the machinery of the biological system.