The difference curve of the MEA-plus-nanocages sample and the MEA-only sample for the MEA resonance wavelength of (A) 674 nm, (B) 777 nm, and (C) 927 nm. The normalized sum of the absolute value of the difference curve can be used to quantify the signal change due to the particles. The normalized sum is 15.3, 40.1, and 65.6 for case (A), (B), and (C), respectively.