Fig. 2.
Nanomorphological and optical properties of the f-PNPs and RGD-f-PNPs/EPI complex. a, b SEM and AFM image of the f-PNPs indicate an average diameter of ~28 nm, which is significantly smaller than most self-assembled peptide nanostructures reported in the literature. Scale bar: 100 nm. c PXRD spectrum with distinct sharp peaks and high intensities indicates well-ordered nanocrystal structure of the f-PNPs. d Fluorescence vs. excitation spectra indicating multiple emission signals under various excitation wavelengths. Both visible and NIR fluorescence emissions were observed. e Mass spectra of RGD-f-PNPs after nanoparticle disassembly. The molecular weight of 1243.550 indicates the successful conjugation between RGD and cyclo[-(d-Ala-l-Glu-d-Ala-l-Trp)2-] peptides. The molecular weight of 937.351 indicates the unconjugated cyclo[-(d-Ala-l-Glu-d-Ala-l-Trp)2-] peptides. f, g Fluorescence emission spectra of the RGD-f-PNPs. Excitation wavelengths are 370 and 760 nm, respectively. No obvious fluorescence change was observed for f-PNPs after the RGD modification. h, i Fluorescence emission spectra of the EPI alone, RGD-f-PNPs before and after EPI loading. Excitation wavelengths are 370 and 760 nm, respectively. Obvious fluorescence quenching was observed after EPI loading