Fig. 1.

SNARF-5F encapsulated polyacrylamide based nanoparticle (NP) synthesis and pH-sensing scheme. a Two-step synthesis schematic of SNARF-5F encapsulated acrylamide-based NP. The surface of the SNARF-PAA NP is modified with polyethylene glycol, for immune system avoidance, and with the tumor-homing F3 peptides. The normalized optical absorption spectra at different pH levels indicate the SNARF-PAA NP’s capability of pH sensing. The absorption at 565 nm, i.e., the isosbestic point, can be used as an internal reference point. The absorption at 600 nm can be used as a sensing point, which responds to difference in pH level. b PA pH-sensing scheme. The PA signal increases linearly with the optical absorption of NPs. Thus, the PA signal amplitude at 600 nm changes as the environmental pH changes; while the PA signal amplitude at 565 nm remains unchanged, acting as an internal reference signal