A Highly Sensitive and Selective Surface-Enhanced Nanobiosensor
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A Highly Sensitive and Selective Surface-Enhanced Nanobiosensor Amanda J. Haes and Richard P. Van Duyne Department of Chemistry, Northwestern University, Evanston, IL 60208-3113, USA ABSTRACT Nanosphere lithography (NSL) derived triangular Ag nanoparticles were used to create an extremely sensitive and specific optical biological and chemical nanosensor. Using simple UV-vis spectroscopy, biotinylated surface-confined Ag nanoparticles were used to detect streptavidin down to one picomolar concentrations. The system was tested for nonspecific binding interactions with bovine serum albumin and was found to display virtually no adverse results. The extremely sensitive and selective response of the Ag nanoparticle sensor indicates an exciting use for biological and chemical sensing. INTRODUCTION Currently, there is great interest in the optical properties of noble metal nanoparticles. Early work with size tunable Ag nanoparticles fabricated by nanosphere lithography (NSL) demonstrated that the localized surface plasmon resonance (LSPR) could be tuned throughout the visible region of the electromagnetic spectrum [1]. The LSPR, the signature optical property of noble metal nanoparticles, arises when electromagnetic radiation excites the conduction electrons of the metal and causes them to oscillate collectively. The primary consequences of this excitation include (a) localized electromagnetic field enhancement and is responsible for the intense signals observed in surface-enhanced spectroscopies and (b) selective photon absorption/scattering (extinction) and can be easily monitored using UV-vis spectroscopy [2]. The formation of alkanethiol self-assembled monolayers (SAMs) on metal surfaces (i.e. nanoparticles) offers a simple and attractive method of surface modification. SAMs are used in many chemical and biological sensor technologies because they can functionalize a metal nanoparticle for specific analyte capture and protect fragile biological molecules from denaturing upon exposure to bare metal surfaces [3-5]. These systems have been implemented in various detection schemes with the goal of creating biosensing systems. SAMs have been used to link molecules from solution onto nanoparticles and bulk surfaces [6-8]. The extremely high binding affinity of the biotin-streptavidin complex (~1013 – 1015 M-1 ) [9] makes SAM modified Ag nanoparticles ideal for model biosensing experiments . The detection of low concentrations of biomolecules with minimal nonspecific binding responses is an elusive goal in many biosensor technologies. Streptavidin (SA), a tetrameric protein, can bind up to four biotinylated molecules (i.e. antibodies, inhibitors, nuclei acids, etc.) with minimal impact on its biological activity [10]. These complexes are extremely stable over a wide range of pH and temperature; accordingly, this system is often used to test potential biosensor systems. Surface plasmon resonance biosensors have been used to characterize the specific binding of a biomolecule to its immobilized binding partner. These propagating
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