Pc/Nc-based agents for probing biological processes. (a) Multiplexed in vivo tumor PA imaging. Representative 2D slice images exhibiting US (first row), cRGD NP PA (second row), unmodified NP PA (third row), blood PA (fourth row), and overlaid signals (fifth row), and example 3D reconstruction (sixth row) of mice tumors, 48 h after tail vein inoculation with 5% cRGD NPs + 0% cRGD NPs (left column) and 25% cRGD NPs + 0% cRGD NPs (right column), respectively. Reprinted with permission from Lu et al., ACS Biomater. Sci. Eng. 3(3), 443 (2017). Copyright 2017 American Chemical Society. (b) Representative PA MAP images of tumors for BSO-pretreated and untreated mice after systemic administration of PCBP (30 μg per mouse) through tail vein. Republished with permission from Xie et al., Adv. Mater. 29(44), 1703693 (2017). Permission conveyed through Copyright 2017 John Wiley and Sons Clearance Center, Inc. (C) (i) Schematic of the nanosensor 2-step binding mechanism between IFNγ and its receptors. (ii) Response of the IFNγ nanosensor (780 nm) to buffer and 10 μM IFNγ (169 μg/ml) in buffer. Error bars represent the standard deviation of three independent trials. Reprinted with permission from Morales et al., ACS Sens. 4(5), 1313 (2019). Copyright 2019 American Chemical Society. PA, photoacoustic; US, ultrasound.