For the levodopa measurements in human blood serum (prod. no. 11405055, Fisher scientific), the SWCNTs (1 nM) were diluted in PBS and serum to reach 20 % or 100 % serum concentration. The mixture was incubated in a refrigerator overnight. The well plate was prepared and measured the same way as without serum. The intensities measured with the spectrometer were analyzed by subtracting a background spectrum (PBS)and taking the peak value of the spectrum at around 990 nm.