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One of the thy problems currently impeding the applications of the fluorescence imaging technique is the poor spatial resolution in deep tissue.Ultrasound-switchable fluorescence (USF) imaging is a novel imaging tool that has recently been explored to possibly surmount the above-mentioned bottleneck.Herein,a β-cyclodextrin/indocyanine green (ICG) complex-encapsulated poly(N-isopropylacrylamide) (PNIPAM) nanogel was synthesized and studied for ex vivo/in vivo deep tissue/high-resolution near infrared USF (NIR-USF) imaging.To be specific,our results revealed that the average diameter of the as-prepared nanogels was significantly decreased to ～ 32 nm from ～ 335 nm compared to the reported ICG-PNIPAM nanoparticles.Additionally,the excitation/emission characteristics of the ICG itself in present nanogels were almost completely retained,and the resultant nanogel exhibited high physiological stability and positive biocompatibility.In particular,the signal-to-noise ratio of the USF image for the PNIPAM/β-cyclodextrin/ICG nanogel (33.01 ± 2.42 dB) was prominently higher than that of the ICG-PNIPAM nanoparticles (18.73 ± 0.33 dB)in 1.5-cm-thick chicken breast tissues.The NIR-USF imaging in 3.5-cm-thick chicken breast tissues was achieved using this new probe.The ex vivo NIR-USF imaging of the mouse liver was also successfully obtained.Animal experiments showed that the present nanogels were able to be effectively accumulated into U87 tumor-bearing mice via enhanced permeability and retention effects,and the high-resolution NIR-USF imaging of in vivo tumor was efficiently acquired.The metabolism and in vivo biodistribution of the nanogels were evaluated.Overall,the results suggest that the current nanogel is a highly promising NIR-USF probe for deep tissue and high-resolution USF imaging.