Fluorescence has been observed directly across the band gap of semiconducting carbon nanotubes. We obtained individual nanotubes, each encased in a cylindrical micelle, by ultrasonically agitating an aqueous dispersion of raw single-walled carbon nanotubes in sodium dodecyl sulfate and then centrifuging to remove tube bundles, ropes, and residual catalyst. Aggregation of nanotubes into bundles otherwise quenches the fluorescence through interactions with metallic tubes and substantially broadens the absorption spectra. At pH less than 5, the absorption and emission spectra of individual nanotubes show evidence of band gap-selective protonation of the side walls of the tube. This protonation is readily reversed by treatment with base or ultraviolet light.

No abstract

cancer cells ͉ optical excitation ͉ radiation therapy ͉ drug delivery nanobiotechnology

The addition of oxaliplatin to weekly FULV significantly improved DFS in patients with stage II and III colon cancer. FLOX can be recommended as an effective option in clinical practice.

A B S T R A C T PurposeAlthough chemoradiotherapy plus resection is considered standard treatment for operable rectal carcinoma, the optimal time to administer this therapy is not clear. The NSABP R-03 (National Surgical Adjuvant Breast and Bowel Project R-03) trial compared neoadjuvant versus adjuvant chemoradiotherapy in the treatment of locally advanced rectal carcinoma. Patients and MethodsPatients with clinical T3 or T4 or node-positive rectal cancer were randomly assigned to preoperative or postoperative chemoradiotherapy. Chemotherapy consisted of fluorouracil and leucovorin with 45 Gy in 25 fractions with a 5.40-Gy boost within the original margins of treatment. In the preoperative group, surgery was performed within 8 weeks after completion of radiotherapy. In the postoperative group, chemotherapy began after recovery from surgery but no later than 4 weeks after surgery. The primary end points were disease-free survival (DFS) and overall survival (OS). ResultsFrom August 1993 to June 1999, 267 patients were randomly assigned to NSABP R-03. The intended sample size was 900 patients. Excluding 11 ineligible and two eligible patients without follow-up data, the analysis used data on 123 patients randomly assigned to preoperative and 131 to postoperative chemoradiotherapy. Surviving patients were observed for a median of 8.4 years. The 5-year DFS for preoperative patients was 64.7% v 53.4% for postoperative patients (P ϭ .011). The 5-year OS for preoperative patients was 74.5% v 65.6% for postoperative patients (P ϭ .065). A complete pathologic response was achieved in 15% of preoperative patients. No preoperative patient with a complete pathologic response has had a recurrence. ConclusionPreoperative chemoradiotherapy, compared with postoperative chemoradiotherapy, significantly improved DFS and showed a trend toward improved OS.

In acidic solution between pH 6 and 2.5, protons react reversibly and selectively in the presence of preadsorbed oxygen at the sidewall of aqueous dispersed single-walled carbon nanotubes suspended in sodium dodecyl sulfate. This reactive complex, which protonates the nanotube sidewall, reversibly diminishes absorption intensity, fluorescent emission, and resonant Raman scattering intensity. The results document the first evidence of electronic selectivity with metallic nanotubes reacting initially near neutral pH, followed by successive protonation of nanotubes with increasing band gap as the solution is increasingly acidified. Preadsorption of molecular oxygen is shown to play a critical role in the interaction, and its desorption kinetics is followed using UV irradiation. The role of the charged electric double layer of the surfactant is discussed. This chemistry, which proceeds under relatively mild conditions, holds promise for separating nanotubes by metal and semiconducting types.

Chiral selective reactivity and redox chemistry of carbon nanotubes are two emerging fields of nanoscience. These areas hold strong promise for producing methods for isolating nanotubes into pure samples of a single electronic type, and for reversible doping of nanotubes for electronics applications. Here, we study the selective reactivity of single-walled carbon nanotubes with organic acceptor molecules. We observe spectral bleaching of the nanotube electronic transitions consistent with an electron-transfer reaction occurring from the nanotubes to the organic acceptors. The reaction kinetics are found to have a strong chiral dependence, with rates being slowest for large-bandgap species and increasing for smaller-bandgap nanotubes. The chiral-dependent kinetics can be tuned to effectively freeze the reacted spectra at a fixed chiral distribution. Such tunable redox chemistry may be important for future applications in reversible non-covalent modification of nanotube electronic properties and in chiral selective separations.

Composite electrodes composed of silicon nanowires synthesized using the supercritical fluid؊liquid؊solid (SFLS) method mixed with amorphous carbon or carbon nanotubes were evaluated as Li-ion battery anodes. Carbon coating of the silicon nanowires using the pyrolysis of sugar was found to be crucial for making good electronic contact to the material. Using multiwalled carbon nanotubes as the conducting additive was found to be more effective for obtaining good cycling behavior than using amorphous carbon. Reversible capacities of 1500 mAh/g were observed for 30 cycles.