Towards fluorescence microscopy with an STM

Fluorescence spectroscopy has advanced our understanding of biological processes and structures through the development of probes that may be attached to specific points of interest. Though a powerful tool, fluorescence spectroscopy has always been limited by resolution. In an attempt to increase resolution, we have built a scanning tunneling microscope that can capture light emitted while scanning, and we tested our apparatus by examining light emission from surface plasmons excited by tunneling electrons from the STM tip. We then used the STM to observe DNA attached to a gold substrate and found that DNA quenches plasmon emission. We also found that both non-labelled and fluorescent-labelled DNA have light emission images that change when repeatedly scanned. We argue that these changes are due to DNA damage by low energy (< 3eV) tunneling electrons.