(a) Overlaid 2D and 3D ultrasound and photoacoustic (PA) images of the U87MG tumor mice treated with CNTR, CNT@AuNP, CNTR@AuNS, and CNTR@AuNP, respectively, at different time points after intravenous injection. Average PA amplitude (b) and PA spectra (c) of the tumor tissues treated with CNTR, CNT@AuNP, CNTR@AuNS, and CNTR@AuNP, respectively, at different time points after intravenous injection. (d) Photoacoustic microscopy (PAM) image of a tumor grown on the mouse ear. (d1) Photograph of the UVA-C2 renal cell carcinoma (RCC) xenograft tumor model on the mouse ear. PAM image of the tumor before (d2) and 140 h after the administration of CNTR@AuNP and being illuminated with a 808 nm laser (d3). (e) PA intensity of the tumor region before and at 24 and 140 h post-injection of CNTR@AuNP.