Abstract
Gold-DNA conjugates were investigated in detail by a comprehensive gel electrophoresis study based on 1200 gels. A controlled number of single-stranded DNA of different length was attached specifically via thiol-Au bonds to phosphine-stabilized colloidal gold nanoparticles. Alternatively, the surface of the gold particles was saturated with single stranded DNA of different length either specifically via thiol-Au bonds or by nonspecific adsorption. From the experimentally determined electrophoretic mobilities, estimates for the effective diameters of the gold-DNA conjugates were derived by applying two different data treatment approaches. The first method is based on making a calibration curve for the relation between effective diameters and mobilities with gold nanoparticles of known diameter. The second method is based on Ferguson analysis which uses gold nanoparticles of known diameter as reference database. Our study shows that effective diameters derived from gel electrophoresis measurements are affected with a high error bar as the determined values strongly depend on the method of evaluation, though relative changes in size upon binding of molecules can be detected with high precision. Furthermore, in this study, the specific attachment of DNA via gold-thiol bonds to Au nanoparticles is compared to nonspecific adsorption of DNA. Also, the maximum number of DNA molecules that can be bound per particle was determined.
Highlights
DNA-functionalized gold nanoparticles are an interesting system with applications ranging from biological sensors to the construction of self-assembled materials
The attachment of DNA to Au nanoparticles can be clearly observed by gel electrophoresis [9, 11, 13, 26,27,28, 36,37,38]
In agreement with previous reports, we assume throughout this manuscript that attachment of DNA to Au nanoparticles in first order increases the effective diameter of the conjugates which can be directly seen in the retardation of the band of the conjugates in gel electrophoresis experiments [9, 11, 26,27,28, 36,37,38]
Summary
DNA-functionalized gold nanoparticles are an interesting system with applications ranging from biological sensors to the construction of self-assembled materials. Experiments are based on attaching single-stranded DNA molecules via thiol-gold bonds to the surface of Au nanoparticles and a subsequent self-assembly process of these conjugates by making use of base pairing of complementary DNA molecules [1,2,3,4,5]. By employing Au-DNA conjugates, several groups have developed schemes to detect target DNA sequences [6] and to assemble nanoparticles into macroscopic materials [7, 8]. DNA-functionalized Au nanoparticles are the building blocks for the above-mentioned experiments. Due to the high affinity of thiol groups to gold surfaces, thiol-modified DNA molecules can be directly bound to the
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