西亚试剂：On the basis of the fluorescence dye tests

Figure 3 Scanning electron microscopy (SEM) images of E. coli. (a) Cells incubated without SWNTs for 60 min. Cells were filtered and observed via SEM on the filter. (b) Cells incubated with SWNTs for 60 min.

On the basis of the fluorescence dye tests (Figure 2) and SEM images (Figure 3), we conclude that E. coli cells in contact with SWNT aggregates or an SWNT-deposited layer suffered membrane damage that likely resulted in compromised membrane permeability. The apparent cell damage should have led to an efflux of cytoplasmic materials into the solution. We proved the efflux of cytoplasmic materials by two independent measurements, namely, the concentrations of DNA and RNA in solutions of E. coli cells incubated with and without SWNTs. Even without taking into account the adsorption of plasmid DNA and RNA to SWNTs, we measured more than a 5-fold increase of plasmid DNA and a 2-fold increase of RNA in solutions in contact with SWNTs. The significant increase in the concentration of plasmid DNA and RNA in the presence of SWNTs confirms the severe damage to cell membrane integrity.

Although our results show that the E. coli undergoes severe membrane damage and subsequent loss of viability due to SWNTs, very little information is currently available with regard to the cytotoxic mechanisms of SWNTs. Previous studies, mainly focusing on mammalian cells, have proposed three principal cytotoxic mechanisms: oxidative stress,9 metal toxicity,20 and physical piercing.6 Of these, our results showed that metal toxicity was not an important mechanism of SWNT toxicity because we were effectively able to purify the SWNTs, resulting in residual metal catalyst (mainly Co) measuring less than 0.8 wt % (which is equivalent to 40 ppb). Several studies have proposed oxidative stress as a direct cause of membrane damage with carbon-based nanomaterials, which is caused by lipid peroxidation within the mammalian cell.8,9,12 However, these studies centered around the presence of residual metals within CNTs, which may lead to oxidative stress.21 In fact, recent studies suggest that the physical interaction of carbon-based nanomaterials (fullerene) with cells, rather than oxidative stress, is the primary killing mechanism.22,23

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