Mono and dialkoxysilane surface modification of superparamagnetic iron oxide nanoparticles for application as magnetic r
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Kendall M. Hurst and W. Robert Ashurst Department of Chemical Engineering, Auburn University, Auburn, Alabama 36849
Natalie J. Serkova Department of Anesthesiology, University of Colorado, Cancer Center Imaging Core, Anschutz Medical Center, Aurora, Colorado 80045
Conrad R. Stoldta) Department of Mechanical Engineering, University of Colorado, Boulder, Colorado 80401 (Received 12 January 2012; accepted 2 May 2012)
In this study, we have developed and characterized two previously unstudied alkoxysilane surface chemistries for use with superparamagnetic iron oxide (SPIO) nanoparticles as a magnetic resonance imaging contrast agent. We modified superparamagnetic iron oxide nanoparticles (SPIO) using aminopropyl triethoxysilane and two analogous alkoxysilanes, aminopropyl dimethylethoxysilane and aminopropyl methyldiethoxysilane, to compare a mono- and dialkoxysilane, respectively, to a more commonly used trialkoxysilane as two new SPIO surface chemistries capable of forming ultrathin functional surface coatings. The ligand densities of the mono- and dialkoxysilane-modified SPIO produced in this study are consistent with near monolayers of ligands on the SPIO surface. We studied the chemical stability of the mono-, di-, and trialkoxysilane-modified SPIO in neutral and acidic media to evaluate the viability of these surface chemistries for use in long-term intracellular applications. The monoand dialkoxysilane-modified SPIO demonstrate comparable chemical stability to the trialkoxysilane-modified SPIO, indicating that the mono- and dialkoxysilane are both viable new SPIO surface chemistries for future applications requiring minimally thick alkoxysilane surface coatings.
I. INTRODUCTION
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.160
Aminopropyl triethoxysilane (APS3) is arguably the most commonly used functionalized alkoxysilane due to the versatile nature of the amine functionalization of the SPIO surface after silanization with APS3. As shown in Fig. 1(a), APS3 possesses three hydrolyzable alkoxy anchor groups and may form Fe–O–Si bonds with the SPIO surface but may also oligomerize by forming Si–O–Si bonds with other APS3 molecules. This oligomerization of APS3 is disadvantageous because it results in a thick silica shell due to the condensation of multiple molecular layers on the SPIO surface, which reduces the efficacy of the SPIO as a MRI contrast agent by decreasing the saturation magnetization of the nanoparticles.12 A further disadvantage of APS3 oligomerization is the occurrence of interparticle crosslinking, leading to the formation of undesired SPIO aggregates of uncontrolled sizes.14 This undesired oligomerization is inherent to the trialkoxy functionality of APS3 and necessitates careful control of reaction parameters to minimize the silanization thickness and to avoid the crosslinking SPIO aggregates. Despite these disadvantages, APS3 is the de
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Ó Materials Research Society 2012
Superparamagnetic iron oxide nanoparticles (SPIO) are attractive ma
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