Fig. 1 shows the UV–vis spectra of the samples PEG-NPs, GRP–PEG-NP-S40, GRP–PEG-NP-S50, GRP–PEG-NP-M40, GRP–PEG-NP-M50, and GRP–PEG-NP-M60, where the letters S and M refer to the PEG-NPs preparation method as described above, and the numbers 40, 50, and 60 indicate the sonication time