Near-IR Microscopy Images Nanotubes

Daniel S. Burgess

A team of scientists at Rice University in Houston has reported that near-infrared fluorescence microscopy is suitable for the study of single-walled carbon nanotubes. Basic research into these structures, as well as the development of superior fabrication processes and the realization of their use in a variety of applications, requires a means of imaging these tiny tubes. The group suggests that near-IR fluorescence microscopy is an attractive alternative because the complexity and expense of the instrumentation is relatively low compared with electron and scanning microscopies.

Near-infrared fluorescence microscopy and emission spectroscopy are suitable for the visualization of single-walled carbon nanotubes. The emission spectra of the labeled ends in the fluorescence images display spectral shifts that reflectdifferences in the local environment from one end of the bent tube to the other. Courtesy of R. Bruce Weisman.

In a demonstration of the approach, the investigators imaged untagged 0.6- to 1.4-nm-diameter nanotubes using a Nikon TE-2000 inverted microscope and immobilized samples in a polymer film or dispersed in an aqueous solution. A 660-nm laser diode excited fluorescence, with the polarization of the source controlled using a half-wave plate. They collected the response with an Indigo Systems or a Roper Scientific InGaAs camera with a detection range of 900 to 1600 nm as well as with a Horiba Jobin Yvon spectrograph and a Roper InGaAs array detector, which enabled the identification of nanotube species.

Near-IR fluorescence microscopy is limited to a spatial resolution of approximately 1 μm and is unsuitable for use with some types of single-walled nanotubes, including metallic and semimetallic tubes. The scientists note, however, that its relative simplicity and versatility and its compatibility with simultaneous emission spectroscopy outweigh these disadvantages. Moreover, with a potential time resolution on the scale of milliseconds, the technique promises to enable kinetic studies of the structures in liquid media.

Nano Letters, April 15, 2005 (online), doi:10.1021/nl050366f.