Highly Efficient Silver Nanoparticle Formation on Dialdehyde-Modified DNA
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Highly Efficient Silver Nanoparticle Formation on Dialdehyde-Modified DNA Christian T. Wirges1, Jan Timper2, Ulrich Simon2, and Thomas Carell1 1 Department of Chemistry and Biochemistry, LMU Munich, Butenandtstr. 5-13, Haus F, Munich, 81377, Germany 2 Institute of Inorganic Chemistry, RWTH Aachen, Landoltweg 1, Aachen, 52074, Germany ABSTRACT We investigated the efficient nucleation of silver nanoparticles on aldehyde-modified DNA strands. The aldehyde-bearing DNA was prepared by PCR incorporation of diol-modified synthetic deoxyuridine derivatives and subsequent cleavage of the diol groups to aldehyde functions using sodium periodate. Formerly unavailable dialdehyde-bearing DNA could be prepared by this mild and selective method. Both dialdehyde-DNA and monoaldehyde-DNA are capable of inducing silver nanoparticle formation without the addition of any external reductant. Interestingly, dialdehyde-DNA shows a different kinetic behavior and is about four times as efficient in silver nanoparticle formation as monoaldehyde-DNA. These data suggest a potentially unique mechanism of silver nanocluster formation induced by the dialdehyde groups. SEM measurements of fully metallized DNA strands show homogeneous metal coverage and selective metal deposition exclusively on the DNA template.
INTRODUCTION Transition metal nanoparticles of defined morphology are of high interest in catalysis, photochemistry and nanoelectronic applications[1,2,3] as well as in the emerging field of bionanotechnology[4]. By coupling biomolecules to metal nanoparticles, it is feasible to unite biological recognition and self-assembly properties with the unique features of metals on the nanoscale. In this respect, the modification of DNA with metal nanoparticles or nanoclusters[5,6] as well as the full metallization of DNA strands[7] have received considerable attention. Recently, we have reported on the directed deposition of a homogeneous metal coating on sugar-decorated DNA strands[8]. The process consisted of an initial treatment of the DNA with ammoniacal silver solution (Tollens reagent), followed by a development step in which the resulting silver clusters were enlarged to form a contiguous coating. To date, no data are available on the mechanism of silver nanoparticle formation on DNA strands from Tollens solution. However, significant contributions on silver clusters formed by borohydride reduction[5] or by radiolytic reduction in polyanion solution[1a,9] have been published. It has been shown for these cases that silver clusters with a "magic number" of atoms exist, which are stable in aqueous solution and serve as nucleating species for the growth of larger silver nanoparticles. Henglein was able to find evidence that Ag42+ and Ag9+ clusters can exist in polyphosphate solution for up to one hour until they grow and agglomerate to larger silver particles[9a].
We reasoned that by providing DNA with two aldehyde functions attached to the modified nucleobases instead of one in the case of sugar-modified DNA[8a], we can foster
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