Although various types of imaging agents have been developed for photoacoustic (PA) imaging, relatively few imaging agents exhibit high selectivity/sensitivity to the tumor microenvironment for on-demand PA imaging and therapy. Herein, molybdenum-based polyoxometalate (POM) clusters with the highest oxidation state of Mo(VI) (denoted as Ox-POM) were designed as novel agents for redox-activated PA imaging-guided photothermal therapy. Capable of escaping from recognition and capture by the liver and spleen, these renal clearable clusters with ultrasmall size (hydrodynamic size: 1.9 nm) can accumulate in the tumor, self-assemble into larger nanoclusters at low pH, and are reduced to NIR absorptive agents in the tumor microenvironment. Studies in 4T1 tumor-bearing mice indicated that these clusters could be employed for bioresponsive PA imaging-guided tumor ablation in vivo. Our finding is expected to establish a new physicochemical paradigm for the design of PA imaging agents based on clusters, bridging the conventional concepts of "molecule" and "nano" in the bioimaging field.
Nano letters. 2017 Apr 20 [Epub ahead of print]
Dalong Ni, Dawei Jiang, Hector F Valdovinos, Emily B Ehlerding, Bo Yu, Todd E Barnhart, Peng Huang, Weibo Cai
Guangdong Key Laboratory for Biomedical Measurements and Ultrasound Imaging, School of Biomedical Engineering, Shenzhen University , Shenzhen 518060, China., School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology , Wuhan 430073, China., University of Wisconsin Carbone Cancer Center , Madison, Wisconsin 53705, United States.