Figure 2.

Photoacoustic (PA) imaging and intensity data of SMNPs and metal-doped SMNPs. (A) Photoacoustic spectra from 680 to 970 nm indicate a broad peak for all nanoparticle samples from 720 to 760 nm. (B) Gd(III)-SMNPs have the highest photoacoustic signal of nanoparticles doped with Ni, Zn, Cu, Mn, Fe, or Gd. The Gd(III)-doped SMNPs showed the highest photoacoustic signal and SMNPs without doping showed the lowest signal. (C) Photoacoustic imaging intensity of SMNPs and metal-doped SMNPs (Ni, Zn, Cu, Mn, Fe, and Gd). (D) Absorbance data of SMNPs and metal-doped (Ni, Zn, Cu, Mn, Fe, Gd-doped) SMNPs indicated that Gd(III) had the highest absorbance from 700 to 950 nm. (E) Quantification of photoacoustic imaging intensity for live exchanging of Mn(III)-SMNPs with Gd(III). Mn(III)-SMNPs were used to increase the Gd(III) loading via Mn–Gd ion exchange to observe the photoacoustic intensity change in real time with mixing via pipetting. The photoacoustic intensity shows a change in signal upon addition of Gd(III) (1 mg/mL) to Mn(III)-doped SMNPs (0.68 mg/mL); (F, G) Snapshots from the in situ photoacoustic movie at frames 200 and 700, respectively. The scale bar in panels C and G represents 4 mm.