Authors: Melissa R Dewi Geoffry Laufersky Thomas Nann
Publish Date: 2015/07/28
Volume: 182, Issue: 13-14, Pages: 2293-2298
Abstract
Heterodimeric magnetic nanoparticles of the type AuFe3O4 have been synthesised from separately prepared differently shaped spheres and cubes monodisperse nanoparticles This synthesis was achieved by the following steps a Monofunctionalising each type of nanoparticles with aldehyde functional groups through a solid support approach where nanoparticle decorated silica nanoparticles were fabricated as an intermediate step b Derivatising the functional faces with complementary functionalities eg amines and carboxylic acids c Dimerising the two types of particles via amide bond formation The resulting heterodimers were characterised by highresolution TEM Fourier transform IR spectroscopy and other appropriate methodsSketches and simulations of complex nanomachines have been published since the advent of nanosciences in the early ‘90s However the covalent coupling of two different separately synthesised nanoparticles to form a simple heterodimer has turned out to be extremely difficult In this article we show a straightforward and generic strategy to accomplish this initial step into nanoarchitecture design by extending a solid support synthesis method we have developed earlier for the preparation of homodimers 1The synthesis of highquality nanocrystals or nanoparticles has reached a level where monodisperse and welldefined particles can be made of nearly any material This includes metallic semiconducting and magnetic nanoparticles 2 which have been synthesised and used for numerous bioanalytical applications such as magnetic contrast enhancement and sensing 3 4 5 bioimaging 3 6 7 fluorescent marking 8 9 hyperthermia 10 11 and catalysis 12 Interestingly some analytical methods are based on the dimerisation or controlled coagulation of individual nanoparticles 13 14 It is known that the properties and performance of nanoparticles are strongly affected by the shape size crystalline structure as well as the monodispersity of the materials 15 16 17 Although it is possible to tune the properties of nanoparticles by modifying these attributes there are limits in engineering chemical and physical properties To overcome these restrictions seedmediated growth methods have been developed for a number of materials resulting in multifunctional particles 18 19 While these techniques are advantageous they are severely limited in the choice of materials due to the degree of chemical compatibility required for the techniques eg lattice mismatch redox behaviour and defect formation The covalent linkage of two different nanoparticles constitutes the first step in extending the range of engineerable properties and paves the road for higher complexity nanosystemsOur method is substantially different from the seedmediated methods mentioned above and biomolecule supported strategies for example using deoxyribonucleic acid DNA that led to controlled nanoparticle assemblies in the past 20 21 The monofunctionalisation strategy used in this work is grounded in modifying nanoparticles selectively at their point of contact to a much larger surface 1 22 23 This strategy follows a similar approach to Merrifield peptide synthesis thus Merrifield resin 24 25 and a range of other commercial supports such as polymer Wang resin 26 were considered initially However none of the commercial supports were suitable for our strategy as it was found that they tend to wrap the nanoparticles impeding monofunctionalisation and making it difficult or impossible to separate from the nanoparticles after the reaction Silica nanoparticles SiO2 NPs were selected as a means of providing this rigid stable and highsurface area structural support and were successfully used for a different type of monofunctionalisation earlier 1Silica nanoparticles with an average diameter of about 50 nm were synthesised via the Stöber method 27 28 29 30 a size histogram is available in the supporting information Figure S4 The silica particles were subsequently aminated with 3aminopropylethoxysilane APTES and functionalisatized with a cleavable linker via ethyl dimethylaminopropylcarbodiimide / Nhydroxysuccinimide EDC/NHS conjugation Tartaric acid C4H6O6 was chosen as it can be cleaved by oxidation at its vicinal alcohol groups using sodium periodate NaIO4 supporting information Figure S5 The dually carboxylateterminated molecule also allows for further functionalization via EDC/NHS peptide bond formation
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