Design of a Biocompatible and Optically-Stable Solution-Phase Substrate for SERS Detection
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1133-AA09-02
Design of a Biocompatible and Optically-Stable Solution-Phase Substrate for SERS Detection Maryuri Roca, Prescott M. Mackie, and Amanda J. Haes University of Iowa, Department of Chemistry, 204 IATL Iowa City, Iowa 52242, U.S.A. ABSTRACT Detection of important biological molecules using surface-enhanced Raman scattering (SERS) has become widely used because of the highly sensitive and label free approach offered by SERS as well as the low cytotoxic response from some SERS substrates. Gold nanoparticles are commonly used in SERS studies; however, the inherent instability of these metal nanostructures in solution adversely influences the reproducibility and quantitative nature of these measurements. Furthermore, the metal surface often denatures biomolecules upon their direct interaction. To combat this incompatibility and improve optical stability, gold nanoparticles have been encapsulated in silica shells. These Au@SiO2 nanostructures have been used extensively in cellular studies, but their SERS capabilities are generally limited to uses that include silica-entrapped SERS reporter molecules rather than direct SERS detection. This work focuses on combating these limitations via the fabrication of Au@SiO2 nanoparticles with porous silica membranes for the direct detection of target molecules in solution. Gold nanoparticles have been designed and coated with a variety of silica morphologies and subsequently interrogated using extinction spectroscopy and SERS. It will be revealed that these gold nanoparticles entrapped in silica membranes serve as optically stable substrates for the quantitative and direct detection of target molecules. These advances in nanomaterial fabrication are envisioned to impact both fundamental and applied studies in a variety of research areas including catalysis, separations, and spectroscopy. INTRODUCTION Surface-enhanced Raman scattering (SERS), similar to normal Raman scattering, provides unambiguous molecular identification based on the unique Raman fingerprint of molecules. In addition, water is largely Raman-inactive thereby making both Raman and SERS compatible in biological studies. In contrast to normal Raman scattering, SERS relies on the interaction of specific molecules with nanoscale roughened metal surfaces which induce signal enhancements up to 14 orders of magnitude versus normal Raman scattering.1 Despite this large increase in sensitivity, SERS is limited by poor signal reproducibility. In the solution phase, this irreproducibility has been attributed to changes in the electromagnetic or localized surface plasmon resonance (LSPR) properties of metal nanoparticles2 which is a consequence of nanoparticle aggregation. Robust protection against nanoparticle aggregation has been achieved by coating the metal nanoparticle core with a silica shell. Silica is biocompatible, optically transparent, and can be used to tune the optical properties of metal nanoparticles. Moreover, silica is a versatile matrix that allows the design of shells with diverse morphologies and fu
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