Investigating the Fundamental Optical Properties of Single Zinc Oxide Nanorods as an Optical Waveguide for Biomedical Applications

Abstract

The superior optical properties of zinc oxide nanorods (ZnO NRs) have continued to promote their broad use in photonics, light detecting, and biosensing applications due to their waveguiding properties. One particularly important property pertinent to biodetection is fluorescence intensification on nanorod ends (FINE), a phenomenon in which a spatially localized and intensified fluorescence signal with extended photostability at the NR ends is present in the emission profiles of fluorophore-coupled biomolecules on ZnO NRs. Understanding the key parameters affecting the FINE and the degree of FINE (DoF) is critical for further development of ZnO NRs in biosensor applications.

First, I present the outcomes of polarization-resolved measurements and effects of polarization on FINE and DoF. More specifically, I examined the light-matter interaction geometry of the ZnO NR main axis in respect to the polarization of incident excitation by controlling the polarization of the collected emission. The results show that the FINE phenomenon is greatly affected by the polarization state of the excitation source and the highest DoF can be achieved when both the excitation source and collected emission polarization states are perpendicular to the NR main axis. Secondly, I present results of multiphoton-produced optical signals waveguided through a single ZnO NR using scanning offset-emission hyperspectral microscopy that show the waveguiding capabilities of sum-frequency generation, deep-trap emissions, and coherent anti-Stokes Raman scattering signals of ZnO NRs as a function of measurement position, light-matter interaction geometry, and the optical origin of the guided signal. Lastly, I demonstrate a straightforward and effective method to synthesize vertically oriented, Cu-doped ZnO NRs using a novel multipurpose platform of copper silicide nanoblocks that preform laterally in well-defined directions on Si.