General and versatile methods for the functionalization of superparamagnetic, silica-coated, maghemite nanoparticles by surface amino and/or carboxyl groups have been established. The nanoparticles were synthesized using co-precipitation from aqueous solutions and coated with a thin layer of silica using the hydrolysis and condensation of tetraethoxysilane (TEOS). For the amino functionalization, 3-(2-aminoethylamino)propylmethyldimethoxysilane (APMS) was grafted onto the nanoparticle surfaces in their aqueous suspensions. The grafting process was followed by measurements of the ζ-potential and a determination of the concentration of the surface amino groups with conductometric titrations. The surface concentration of the amino groups could be varied by increasing the amount of APMS in the grafting process up to approximately 2.3 –NH2 groups per nm2. The carboxyl functionalization was obtained in two ways: (i) by a ring-opening linker elongation reaction of the surface amines at the functionalized nanoparticles with succinic anhydride (SA) in non-aqueous medium, and (ii) by reacting the APMS and SA first, followed by grafting of the carboxyl-terminated reagent onto the nanoparticle surfaces. Using the first method, the SA only reacted with the terminal primary amino groups (–NH2) of the surface-grafted APMS molecules. Infra-red spectroscopy (ATR FTIR) and mass spectrometry (HRMS) showed that the second method enables the bonding of up to two SA molecules per one APMS molecule, since the SA reacted with both the primary (–NH2) and secondary amino (–NH–) groups of the APMS molecule. When using both methods, the ratio between the surface amino and carboxyl groups can be controlled.
Surface functionalization Magnetic nanoparticles Silanes Amino functionalization Carboxyl functionalization Coatings
This is a preview of subscription content, log in to check access
The support of the Ministry of Higher Education, Science and Technology of the Republic of Slovenia within the National Research Program is gratefully acknowledged. The authors also thank Dr Anamarija Zega from the University of Ljubljana for the ATR-FTIR measurements and Dr Bogdan Kralj from the Centre of Excellence for Environmental Technologies for the MS analyses.
Levy L, Sahoo Y, Kim K, Bergey EJ, Prasad PN (2002) Nanochemistry: synthesis and characterization of multifunctional nanoclinics for biological applications. Chem Mater 14:3715–3721. doi:10.1021/cm0203013CrossRefGoogle Scholar
Mahalingam V, Onclin S, Peter M, Ravoo BJ, Huskens J, Rein-Houdt DB (2004) Directed self-assembly of functionalized silica nanoparticles on molecular printboards through multivalent supramolecular interactions. Langmuir 20:11756–11762. doi:10.1021/la047982wCrossRefGoogle Scholar
Makovec D, Košak A, Žnidaršič A, Drofenik M (2005) The synthesis of spinel-ferrite nanoparticles using precipitation in microemulsions for ferrofluid applications. J Magn Magn Mater 289:32–35. doi:10.1016/j.jmmm.2004.11.010CrossRefGoogle Scholar
Moon JH, Shin JW, Kim SY, Park JW (1996) Formation of uniform aminosilane thin layers: an imine formation to measure relative surface density of the amine group. Langmuir 12:4621–4624. doi:10.1021/la9604339CrossRefGoogle Scholar
Schiestel T, Brunner H, Tovar GEM (2004) Controlled surface functionalization of silica nanospheres by covalent conjugation reactions and preparation of high density streptavidin nanoparticles. J Nanosci Nanotechnol 4:504–511. doi:10.1166/jnn.2004.079CrossRefGoogle Scholar
Socrates G (1994) Infrared characteristic group frequencies. Wiley, New YorkGoogle Scholar
Weissleder R, Kelly K, Sun EY, Shtatland T, Josephson L (2005) Cell-specific targeting of nanoparticles by multivalent attachment of small molecules. Nat Biotechnol 23:1418–1423. doi:10.1038/nbt1159CrossRefGoogle Scholar
Yamaura M, Camilo RL, Sampaio LC, Macedo MA, Nakamura M, Toma HE (2004) Preparation and characterization of (3-aminopropyl)triethoxysilane-coated magnetite nanoparticles. J Magn Magn Mater 279:210–217. doi:10.1016/j.jmmm.2004.01.094CrossRefGoogle Scholar
Yang J, Lim E-K, Lee E-S, Suh J-S, Haam S, Huh Y-M (2010) Magnetoplex based on MnFe2O4 nanocrystals for magnetic labeling and MR imaging of human mesenchymal stem cells. J Nanopart Res 12:1275–1283. doi:10.1007/s11051-009-9837-1CrossRefGoogle Scholar
Yoshinaga K, Nakashima F, Nishi T (1999) Polymer modification of colloidal particles by spontaneous polymerization of surface active monomers. Colloid Polym Sci 277:136–144. doi:10.1007/s003960050378CrossRefGoogle Scholar