Optical characterization of a 1-D nanostructure by dark-field microscopy and surface plasmon resonance to determine biomolecular interactions

This paper presents a multifunctional imaging system that combines dark-field microscopy (DFM) with spectroscopy to image nanostructures and identify their optical properties from absorption spectra. The optical resolving power of this system is determined using a 1-D nanostructure with pitches of 120, 390, and 770 nm with four formats of optical disks. These pattern sizes are verified by atomic force microscopy (AFM) first. The results demonstrate that the resolving power of current system setup can down to 86 nm. The resultant DFM images appear to be slightly larger than the AFM images. A 50-nm-thick gold film was then deposited on top of these nanostructures, and their absorption spectra were obtained to elucidate its optical properties, enhanced by surface plasmon resonance. The immobilization of streptavidin on the surface of gold-coated nanostructure causes the absorption spectra to shift from 600 to 610 nm. A protein nanoarray with a dot size of 50 nm was also imaged by DFM, and can be implemented as a potential biochemical diagnostic system on an optical disk format. Specimens of adenocarcinoma cells and ovary cancer cells were also imaged using this DFM system, and the nuclei structure and some cellular organs can be recognized using a 100× objective oil lens.