Optical spectroscopy of single-walled carbon nanotubes in high magnetic fields

Magnetic flux threading a single-walled carbon nanotube (SWNT) is predicted to influence its electronic structure through the Aharonov-Bohm (AB) effect, causing bandgap oscillations and absorption peaks splitting. In order to verify these predictions, near infrared (NIR) photoluminescence (PL) and visible-NIR absorption in the Voigt geometry were measured at room temperature in external magnetic field (B) up to 74 T. The used aqueous surfactant solubilized SWNT samples show excitonic interband absorption peaks coming from a range of nanotube chiralities present in the sample. At fields B > 30 T, PL peaks showed red shifts and changes in peak widths. Magneto-PL spectra were successfully simulated, demonstrating that the observed spectral changes can be understood in terms of magnetic alignment of SWNTs (due to their predicted anisotropy magnetic properties) and B dependent changes of the bandgap due to the AB effect. By using the measured B-induced nanotube alignment and the measured average length of nanotubes in the sample, we estimated SWNT magnetic anisotropy to be 1.4 x 10-5 emu/mol, consistent with theoretical predictions. At B > 55 T, clear absorption peak splittings were observed, with splitting rates of 1 meV/T in good agreement with theoretical predictions. Recent theory predicts a dark singlet exciton state (below the only bright singlet state) which brightens as B is applied. Our observation of two bright excitons at high B demonstrates that magnetic field is indeed capable of brightening dark excitons

Estimation of Magnetic Susceptibility Anisotropy of Carbon Nanotubes Using

We have carried out a magnetophotoluminescence excitation spectroscopy study on micelle-suspended single-walled carbon nanotubes in high magnetic fields. By analyzing field-dependent spectral changes, we determined the degree of magnetic alignment of the observed semiconducting nanotubes at 45 T. This, together with an independently measured length distribution of the nanotubes, allowed us to estimate the magnitude of the magnetic susceptibility anisotropy � | − � ⊥ to be ∼1.4 × 10-5 emu/mol for 1-nm-diameter semiconducting nanotubes. Single-walled carbon nanotubes (SWNTs), either metallic or semiconducting, are predicted to possess novel magnetic properties. 1-3 For example, while a field applied parallel to the tube axis modifies the band structure through the Aharonov-Bohm (AB) phase, leading to a logarithmically divergent paramagnetic susceptibility for metallic tubes, a perpendicular field is predicted to induce lattice instability and distortion. At low magnetic fields (φ, φ0, where φ is the magnetic flux threading the tube and φ0) h/e is the magnetic flux quantum), semiconducting SWNTs are predicte

Nanosensor dosimetry of mouse blood proteins after exposure to ionizing radiation.

Giant magnetoresistive (GMR) nanosensors provide a novel approach for measuring protein concentrations in blood for medical diagnosis. Using an in vivo mouse radiation model, we developed protocols for measuring Flt3 ligand (Flt3lg) and serum amyloid A1 (Saa1) in small amounts of blood collected during the first week after X-ray exposures of sham, 0.1, 1, 2, 3, or 6 Gy. Flt3lg concentrations showed excellent dose discrimination at ≥ 1 Gy in the time window of 1 to 7 days after exposure except 1 Gy at day 7. Saa1 dose response was limited to the first two days after exposure. A multiplex assay with both proteins showed improved dose classification accuracy. Our magneto-nanosensor assay demonstrates the dose and time responses, low-dose sensitivity, small volume requirements, and rapid speed that have important advantages in radiation triage biodosimetry