Immobilization of oligonucleotide-functionalized magnetic nanobeads in DNA-coils studied by electron microscopy and atom
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Immobilization of oligonucleotide-functionalized magnetic nanobeads in DNA-coils studied by electron microscopy and atomic force microscopy Mattias Strömberg1, Sultan Akhtar1, Klas Gunnarsson1, Camilla Russell2, David Herthnek2, Peter Svedlindh1, Mats Nilsson2, Maria Strømme1 and Klaus Leifer1 1
Department of Engineering Sciences, Uppsala University, Ångström Laboratory, Box 534, SE751 21 Uppsala, Sweden. 2 Department of Immunology, Genetics and Pathology, Uppsala University, Rudbeck Laboratory, SE-751 85 Uppsala, Sweden. ABSTRACT Immobilization of oligonucleotide-functionalized magnetic nanobeads by hybridization in DNA-coils formed by rolling circle amplification has been investigated using transmission electron microscopy (TEM) and atomic force microscopy (AFM). The TEM results supported earlier made observations that small beads with low oligonucleotide surface coverage preferably immobilize in the interior of the DNA-coils and do not tend to link several DNA-coils together whereas large beads with high surface coverage to a larger extent connect several DNA-coils together to clusters of several DNA-coils with beads. AFM provided direct visualization of the DNA-coils as thread-like objects. DNA-coils with immobilized beads appeared as a collection of beads with thread-like features in their near vicinity. INTRODUCTION Today, different life science areas require biosensing technologies for detection of biomolecules, for example, DNA, proteins or antibodies that are simple, sensitive, rapid and inexpensive [1]. Traditional biosensors that rely on non-magnetic transduction mechanisms typically use fluorescent, electrochemical or optical analytical tools. These offer a number of advantages, but are also often connected with limitations such as, e.g., expensive instrumentation and time-consuming sample preparations [2-4]. A large variety of biosensors that are currently under development, make use of nanoparticles that are functionalized and operate in an environment of biomolecules. In particular, the use of magnetic micro- and nanoparticles (magnetic beads) in biosensing applications puts forward unique properties, since there is no magnetic background in most biological samples [5]. Furthermore, beads are rather inexpensive to produce, can easily be bio-functionalized and are physically and chemically stable. To develop optimal biosensors using nanoparticles, the details of the interaction and attachment of the nanoparticles with biomolecules must be understood. Though, in principle, structural and chemical order in biological nanoparticles can be visualized [6], to date, there is only a limited range of analysis methodologies available to study such functionalization and interactions in real-space. Recently, we provided a proof-of-principle of a novel magnetic DNA bioassay principle suitable as a platform for low-cost and easy-to-use diagnostic devices; the volume-amplified magnetic nanobead detection assay (VAM-NDA) [7,8]. This biosensor principle is based on the base-pair hybridization of oligonucleotide-funct
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