Due to their unique optical properties, III-V nanowires are promising candidates for the development of efficient solar cells, LEDs and nanoscaled lasers. The interaction of nanowires with fluorescent molecules is also of interest, as these nanostructures can act as nanoscaled optical fibers. The light emitted by a fluorophore close to a nanowire surface can in fact couple into the supported waveguide modes and get re-emitted at the nanowire tip. This thesis explores the possibility of using III-V nanowires to enhance the detection of fluorescent molecules, focusing on the development of a platform to characterize an artificial molecular motor, the Lawnmower, and the possibilities these nanostructures present for optical biosensing.
Confocal imaging was used to investigate the dependence of the lightguiding effect over nanowire diameter and fluorophore emission range, and the role of multiple waveguide modes was identified by comparing experimental data with finite-difference simulations and analytical calculations. These results show how the normalized frequency parameter can be used to predict the lightguiding ability of a nanowire at a certain wavelength, serving as a useful design guide for optimizing the effect for a specific fluorophore.
The potential of nanowires for enhanced fluorescence detection was investigated by coating the nanowires with a supported lipid bilayer containing fluorescently labelled proteins. Diffusion of single proteins from and to the nanowires surface caused the nanowire tips to blink over time, and the parallel observation of the blinking pattern of hundreds of nanowires allowed to estimate simultaneously both protein coverage and diffusion constant in the bilayer.
This thesis also discusses how nanowires can be used as a track and characterization device for the Lawnmower, and the development of the surface chemistry necessary for this scope. These results open the possibility of developing nanowire-based optical biosensors, as due their lightguiding properties nanowires could be used as signal integrators to improve the sensitivity of fluorescence-based assays.