Silica coated Magnetic Nanoparticles (SMNPs): Capture and Identification of Escherichia coli Cells using Surface Enhanced Raman Spectroscopy Shiva K. Rastogi, † Jamie Jabal, ‡ Huijin Zhang, Ϯ Kevin J. Haler, Ϯ Charlene M. Gibson, ‡ You Qiang, † D. Eric Aston, and Ϯ A. Larry Branen Department of Chemistry, University of Idaho, Moscow, ID - 83843, USA, srastogi@uidaho.edu Ϯ Biosensors and Nanotechnology Applications Laboratory, University of Idaho, 1031 N Academic Way, Coeur D’ Alene, ID - 83814, USA, gibsonc@uidaho.edu , lbranen@uidaho.edu † Department of Chemical and Material Engineering, University of Idaho, Moscow, ID - 83844, USA, Jamie@vandals@uidaho.edu , aston@uidaho.edu ‡ Departmental of Physics and Environmental Science, University of Idaho, Moscow, ID - 83844, USA, zhan3921@vandals.uidaho.edu , youqiang@uidaho.edu ABSTRACT Silica coated Magnetic nanoparticles (SMNPs; SiO 2 /Fe 3 O 4 + Fe 2 O 3 ; 75±10 nm in diameter) were prepared by encapsulation of iron oxide NPs with silica dioxide using the sol-gel method and characterized through transmission and scanning electron microscopic imaging, magnetic hysteresis and Fourier transform infrared spectroscopy. The hydroxyl group of SMNPs surface were chemically activated with cyanogens bromide and then functionalized with specific polyclonal antibodies. The functionalized NPs were used to capture and concentrate the environmental Escherichia coli (E. coli) from several local environmentally impacted water streams. The capture of bacteria was confirmed by plating on nutrient agar. Raman spectroscopy was used for detection and monitoring of bacterial disintegration in presence of silver nanoparticles (6±4 nm). Raman spectra of bacterial complex shows the various characteristics biomolecules, this confirms the detection of E. coli captured by SMNPs. This method may ultimately be use as a rapid monitoring procedure for water quality. Keywords: magnetic silica nanoparticles, Escherichia Coli, TEM & SEM, SERS 1 INTRODUCTION The whole cell identification of microorganisms is critical for the food – safety and environmental protection. There are number of conventional method are available for microbial identification [1]. However, most of them are laborious and expensive. The spectroscopic methods like fluorescence [2], mass (MALDI) [3], IR [4] and surface- enhanced Raman spectroscopy (SERS) [5] are currently used to save time. These techniques are capable to identifying a whole microorganism from a limited number of microbial cells in a non-destructive manner. Among, the SERS has drawn attention because it is compatible with biological samples, requires lesser sample preparation and provide signals with detailed information concerning microorganism [6]. SERS, as an analytical tool, has been used in biological applications such as immunoassay, cellular studies, and bacterial detection etc. For achieving significant information from bacterial cell using SERS studies, a colloidal solution of gold (Au) or silver (Ag) nanoparticles (NPs) is required [7]. Commonly, to capture, separate and identify a bacterium from a contaminated sample immunosensor is one of the choices. A typical immunosensor is usually fabricated by immobilizing the specific antibody on the surface of an inert solid support via chemical or physical mechanisms. The iron oxides (Fe 3 O 4 and γ-Fe 2 O 3 ; IO) NPs, possess their unique magnetic property – superparamagnetism, which enables their stability and dispersion after removing the magnetic. Hence, silica coated IO or magnetic NPs (SMNPs) not only offer improved stability but also help to bind the various chemical and biological molecules covalently at the surface of NPs [8]. In our previous report we have shown the synthesis and application of colloidal Ag NPs and Ag cluster over silica NPs for antibacterial activity [9]. Further, in order to identify the different biomolecules upon the action of Ag NPs on bacterial cells and mechanism of action, here we synthesized and characterized SMNPs. The surface hydroxyl groups of these NPs were activated for covalently immobilization of E. coli antibody. These immuno- magnetic (IM) NPs were used to capture magnetic separation and concentrate E. coli from phosphate buffer saline (PBS) suspension. The captured E. coli were treated with colloidal Ag NPs and analyzed using SERS at 1.5 and 2.5 hr of incubation to identify different biomolecules of E. coli. 2 EXPERIMENTAL 2.1 Reagents All the chemicals and reagents were purchased from Sigma Aldrich, (St. Louis, MO, USA) and Fisher Scientific (New Jersey, USA). Polyclonal general goat anti-E. coli antibody was purchased from Viro Stat Inc. (Portland, ME, USA). NSTI-Nanotech 2011, www.nsti.org, ISBN 978-1-4398-7138-6 Vol. 3, 2011 68