Center for Functional Nanomaterials Seminar

The toolset of the modern spectroscopist has rapidly evolved over the past decade. Today, it is possible to observe the emission of photons from a single fluorophore, which has opened up new investigations in the broad field of molecular biophysics. Presented in this talk are three different nanosystems studied using optical methods. First, I will introduce the concept of fluorescence correlation spectroscopy (FCS) and its application to investigate the DNA translocation machinery (the ‘packasome’) of bacteriophage T4 at the single-molecule level. Our experiments show that a single nick in the DNA duplex can stall the packasome motor, whereas DNAs with a large 20 basepair stretch of mismatches (a ‘bubble’) can still be packaged. Secondly, I will discuss the photophysical kinetics of fluorophores, in particular, single-pair Förster resonance energy transfer (spFRET). Single donor and acceptor fluorophores were precisely positioned along the DNA backbone, providing a well defined inter-dye distance. Thirdly, I will present experimental observations on the optical and plasmonic properties of nano-structured metals. Nanohole arrays in opaque silver films display optical properties similar to conventional chromatic filters and lenses. A near-field scanning optical microscope was used to map the near-field and far-field intensity distributions of nanohole arrays illuminated by monochromatic plane waves. The far-field intensity distribution was found to be extremely complex, and displayed evidence of subwavelength confinement of propagating light. These results show considerable promise for plasmonics and nano-optics in the development of a new class of sub-diffraction limited light microscopes, which can potentially increase the resolution of single-molecule optical techniques.