Biological oxidative damage by carbon nanotubes: fingerprint or footprint?

Carbon nanotubes (CNTs) have received much attention for performance and toxicity, but vary substantially in terms of impurity type and content, morphology, and surface activity. This study determined the decrease of antioxidant capacity, defined as biological oxidative damage (BOD), of CNTs-exposed serum. The variability in several physicochemical properties of CNTs and their links to BOD elicited in human serum were explored. Tremendous variation in transition metal type and content (104-fold), specific surface area (SSA, nine-fold), and BOD were observed. Mass specific BOD (mBOD) varied from 0.006-0.187 μmol TEU mg(-1), whereas surface area specific BOD (sBOD) varied from 0.068-0.42 μmol TEU m(-2). The sBOD increased in a stepwise fashion from ∼0.1-0.32 μmol TEU m(-2) for tubes with outer diameter less than 10 nm. The mBOD and sBOD may be useful denominators of surface activity and impurity content and assist in designing safer CNTs.