We investigated the role of hydrogen peroxide and observed the reaction did not appreciably proceed in the absence of hydrogen peroxide (Figure ). The E11 -peak intensity was dependent on peroxide concentration, peaking at 2.5% (w/v) peroxide (Figure ). At higher peroxide concentrations, the fluorescence intensity of both the E11 and E11 -peaks decreased. We surmise that this attenuation was due to the high susceptibility of SWCNT emission to oxidation and reduction, showing loss of fluorescence in both cases. Hydrogen peroxide can act as either a reducing or oxidizing agent dependent on pH and so can quench the fluorescence emission of nanotubes at high concentrations. 2.5% (w/v) hydrogen peroxide was found to be optimal for enhancing functionalization kinetics without leading to appreciable loss of fluorescence (Figure ), and thus was used for future functionalization reactions.