Inorganic nanoparticles as optical sensors of DNA

The 1 - 100 nanometer size range encompasses the dimensions of proteins and DNA. In this size range the bulk properties of inorganic materials become influenced by quantum mechanical effects and become size-dependent. Semiconductor nanoparticles are photoluminescent throughout the visible; the emission maximum is dictated by particle size, nature of the surface, and nature of the bulk material. We have used the photoluminescence of semiconductor nanoparticles to infer how oligonucleotides with unusual structure bind to the nanoparticles, providing insight into local structure and flexibility of the DNA. More recently we have examined the effects of base modifications on these binding events. Metallic nanoparticles can also interact with DNA, and these interactions can be monitored by the visible absorbance spectrum of the nanoparticles and by surface-enhanced Raman spectroscopy (SERS). Metallic surfaces that are rough on the nanometer scale are known to enhance the Raman signals of adsorbates by up to a million-fold. The result of photoluminescence titrations of abasic DNA and SERS DNA-nanoparticle studies will be reported.