Biomaterials that inactivate microbes are needed to eliminate medical device infections. We investigate here the antimicrobial nature of single-walled carbon nanotubes (SWNTs) incorporated within the biomedical polymer poly(lactic-co-glycolic acid) (PLGA). We find Escherichia coli and Staphylococcus epidermidis viability and metabolic activity to be significantly diminished in the presence of SWNT-PLGA, and to correlate with SWNT length and concentration (<2% by weight). Up to 98% of bacteria die within one hour on SWNT-PLGA versus 15-20% on pure PLGA. Shorter SWNTs are more toxic, possibly due to increased density of open tube ends. This study demonstrates the potential usefulness of SWNT-PLGA as an antimicrobial biomaterial.

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Subnanometer single-walled carbon nanotubes (sub-nm SWNTs) were synthesized at different temperatures (600, 700, and 800 degrees C) using CoMn bimetallic catalysts supported on MCM-41 silica templates. The state of the catalyst was investigated using X-ray absorption, and the (n,m) indices of the sub-nm SWNTs were determined from Raman spectroscopy and photoluminescence measurements. We find that the size of the metallic particles that seed the growth of sub-nm SWNTs (diameter approximately 0.5-1.0 nm) is highly sensitive to the reaction temperature. Low reaction temperature (600 degrees C) favors the growth of semiconducting tubes whose diameters range from 0.5 to 0.7 nm. These results were also confirmed by electrical transport measurements. Interestingly, dominant intermediate frequency modes on the same intensity scale as the Raman breathing modes were observed. An unusual "S-like" dispersion of the G-band was present in the Raman spectra of sub-nm SWNTs with diameters <0.7 nm.

The effect of manganese addition to the Co-MCM-41 catalyst on the synthesis of single wall carbon nanotubes (SWNT) by CO disproportionation was characterized. The ratio between the two metals in the MCM-41 framework was varied, and its effect on the resultant SWNT distribution was studied and compared with the results obtained for the monometallic Co-MCM-41 catalyst. Methods including temperature-programmed reduction, X-ray absorption fine structure, thermogravimetric analysis, TEM imaging, and Raman and fluorescence spectroscopy were employed to characterize the behavior of the catalysts under the SWNT synthesis conditions and the diameter and structure distribution of the resultant nanotubes. We found that addition of Mn to the Co-MCM-41 catalyst promotes the growth of SWNT, leading to synthesis of high yield, small diameter SWNT. Manganese does not act in the nucleation of SWNT but acts as an anchoring site for cobalt particles formed during the synthesis process as shown by X-ray absorption.