Hyperspectral Microscopy of Near-Infrared Fluorescence Enables 17-Chirality Carbon Nanotube Imaging

The intrinsic near-infrared photoluminescence (fluorescence) of single-walled carbon nanotubes exhibits unique photostability, narrow bandwidth, penetration through biological media, environmental sensitivity, and both chromatic variety and range. Biomedical applications exploiting this large family of fluorophores will require the spectral and spatial resolution of individual (n,m) nanotube species’ fluorescence and its modulation within live cells and tissues, which is not possible with current microscopy methods. We present a wide-field hyperspectral approach to spatially delineate and spectroscopically measure single nanotube fluorescence in living systems. This approach resolved up to 17 distinct (n,m) species (chiralities) with single nanotube spatial resolution in live mammalian cells, murine tissues ex vivo, and zebrafish endothelium in vivo. We anticipate that this approach will facilitate multiplexed nanotube imaging in biomedical applications while enabling deep-tissue optical penetration, and single-molecule resolution in vivo.

High spatial resolution confocal microscope with independent excitation and detection scanning capabilities

We present the design of a confocal microscope adapted for optical spectroscopy and imaging at cryogenic temperatures. This system is based on the existing approach of partly inserting the optical components of the microscope inside a helium-bath cryostat. It provides a spatial resolution approaching the diffraction limit with a mechanical stability allowing uninterrupted integration times exceeding 10 h and allows keeping track of a single emitter for unlimited periods of time. Furthermore, our design allows scanning the excitation spot and detection area independently of the sample position. This feature provides the means to perform probeless transport experiments on one-dimensional nanostructures. The scanning capabilities of this microscope are fully detailed and characterized using the photoluminescence of single nitrogen dyads at 4.5 K.

Significant enhancement of ferromagnetism in Zn1-xCrxTe doped with iodine as an n-type dopant

The effect of additional doping of charge impurities was investigated in a ferromagnetic semiconductor Zn1-xCrxTe. It was found that the doping of iodine, which is expected to act as an n-type dopant in ZnTe, brought about a drastic enhancement of the ferromagnetism in Zn1-xCrxTe, while the grown films remained electrically insulating. In particular, at a fixed Cr composition of x=0.05, the ferromagnetic transition temperature TC increased up to 300 K at maximum due to the iodine doping from TC=30 K of the undoped counterpart, while the ferromagnetism disappeared due to the doping of nitrogen as a p-type dopant. The observed systematic correlation of ferromagnetism with the doping of charge impurities of both the p and n type, suggesting a key role of the position of Fermi level within the impurity d state, is discussed on the basis of the double-exchange interaction as a mechanism of ferromagnetism in this material.