Fluorescence microscopy visualization of single-walled carbon nanotubes using semiconductor nanocrystals

Carbon nanotube (CNT) based electronic, optical, chemical, and biological devices are in dire need of simple optical microscopy solutions, which can be utilized to image and manipulate CNTs in solution state, many times in biologically relevant aqueous environments. Here, we demonstrate fluorescence visualization of single-walled carbon nanotubes (SWNT) in aqueous solutions using simple light microscopes. For this purpose, stable SWNT dispersions of sodium-dodecyl-sulfonate (SDS) were prepared and mixed with CdSe-ZnS core-shell nanocrystals (quantum-dots (QDs)) functionalized by mercaptoacetic acid. QDs arrange themselves on the sidewalls of SWNTs by virtue of electrostatic interaction between zinc ions in their shell and electronegative oxygen atoms/anions in the sulfonate group of the surfactant, embodying the fluorescence visualization of SWNTs. Transmitted brightfield, SEM, and TEM images also provide clear indication of SWNT sidewalls decorated with these QDs. This visualization technique will facilitate simple optical determination of cluster sizes of CNTs and their manipulation for fabrication of CNT-based devices.