Document Type

Student Presentation

Presentation Date


Faculty Sponsor

Jeunghoon Lee


Metal nanoparticles in general exhibit interesting properties due to their small sizes. This response shows up as an intense absorption band in the visible region making metallic nanoparticles ideal probes for medical imaging as well as for countless other applications. Functionalizing metallic nanoparticles with DNA enables targeted labeling, controlled by their base sequence. Another purpose of functionalization is to attach the nanoparticle to a DNA substrate allowing controlled bottom up engineering of nanoscale devices. Gold or gold-encapsulated silver is usually used for these purposes instead of bare silver due to the ease with which silver is oxidized although silver nanoparticles show more intense plasmon resonance. The functionalization of silver with DNA is difficult because their surfaces are easily oxidized. The goal of this experiment was to attach thiolated DNA strands to bare 5-10 nm silver nanoparticles proving that it can indeed be done without extensive modification of the functionalization procedure. In order for this to be accomplished silver nanoparticles were synthesized using two different methods: a UV light directed growth method and a sodium borohydride/sodium citrate buffered reduction method. The first method resulted in nanoparticles in the 10-15 nm range while the second resulted in smaller particles (5-10 nm). DNA was then attached to purified particles using a process that has previously been applied to gold nanoparticles. The functionalization was verified using UV-Vis spectroscopy (to measure changes in the Plasmon peak and concentration) and the stability of the final product in a 0.3 M sodium chloride solution. Several samples have exhibited minimal peak shifts and minimal concentration loss indicating that little or no silver was oxidized in the functionalization process. These samples also remained stable as the sodium chloride concentration was slowly brought up to 0.3 M. Control samples precipitated out of solution almost immediately upon the addition of sodium chloride. Successful functionalization of silver nanoparticles opens up the way for the addition of functionalized silver particles and their inherent optical properties onto DNA heterostructures where they can then be used as seeds for directed growth of nanowires or nanoprisms. This will be accomplished by adding target strands to the DNA structure that are complimentary to the sequence bound to the nanoparticles which then hybridize with the strands on the nanoparticle resulting the incorporation of the nanoparticle into the DNA heterostructure.