Fig. 2. (A) UV-Visible spectra of DFO only, Fe³⁺ only, Al³⁺ only, DFO + Fe³⁺ and DFO + Al³⁺ solution in nitric acid (pH = 2). (B and C) UV-Vis spectra of SWNT/PL–PEG–DFO in the presence of (black) 0 pM, (red) 10 pM, (green) 30 pM, (blue) 50 pM, (cyan) 70 pM, and (magenta) 90 pM Fe³⁺ and Al³⁺ standard solutions, respectively. (D) The decrease in the absorption of SWNT/PL–PEG–DFOs at 270 nm as a function of the increase in the concentration of Fe³⁺ and Al³⁺.