Micro/nanorobots have long been expected to reach all parts of the human body through blood vessels for medical treatment or surgery. However, in the current stage, it is still challenging to drive a microrobot in viscous media at high speed and difficult to observe the shape and position of a single microrobot once it enters the bloodstream. Here, we propose a new micro-rocket robot and an all-optic driving and imaging system that can actuate and track it in blood with microscale resolution. To achieve a high driving force, we engineer the microrobot to have a rocket-like tripletube structure. Owing to the interface design, the 3D-printed micro-rocket can reach a moving speed of 2.8 mm/s (62 body lengths per second) under near-infrared light actuation in a blood-mimicking viscous glycerol solution. We also show that the micro-rocket robot is successfully tracked at a 3.2-µm resolution with an optical-resolution photoacoustic microscope in blood. This work paves the way for microrobot design, actuation, and tracking in the blood environment, which may broaden the scope of microrobotic applications in the biomedical field.

Photoacoustic (PA) imaging and tracking of stem cells plays an important role in the real-time assessment of cell-based therapies. Nevertheless, the limitations of conventional inorganic PA contrast agents and the narrow range of the excitation wavelength in the first near-infrared (NIR-I) window hamper the applications of PA imaging in living subjects. Herein, we report the design and synthesis of a second near-infrared (NIR-II) absorptive organic semiconducting polymer (OSP)-based nanoprobe (OSPN+) for PA imaging and tracking of stem cells. Comparison studies in biological tissue show that NIR-II light excited PA imaging of the OSPN+ has significantly higher signal-to-noise ratio than NIR-I light excited PA imaging, thereby demonstrating the superiority of the OSPN+ for deep tissue imaging. With good biocompatibility, appropriate size, and optimized surface property, the OSPN+ shows enhanced cellular uptake for highly efficient PA labeling of stem cells. In vivo investigations reveal significant NIR-II PA contrast enhancement of the transplanted OSPN+-labeled human mesenchymal stem cells by 40.6- and 21.7-fold in subcutaneous and brain imaging, respectively, compared with unlabeled cases. Our work demonstrates a class of OSP-based nanomaterials for NIR-II PA stem cell imaging to facilitate a better understanding and evaluation of stem cell-based therapies.

Precise diagnosis and effective treatment of gliomas still remain a huge challenge. Photoacoustic-guided photothermal therapy (PTT) has unique advantages over conventional techniques for brain tumor theranostics, but existing nanoagents for photoacoustic imaging (PAI)-guided PTT are mainly organic small molecules or inorganic nanoparticles, which have the limitations of poor photostability and biocompatibility. Besides, the restricted absorption in the first near-infrared window (NIR-I) of the most existing nanoagents compromises their effectiveness for deep tissue PAI and PTT. We herein develop novel semiconducting polymer nanoparticles (SPNs) that are strongly absorptive in the second NIR window (NIR-II) to alleviate these problems. With the merits of excellent photoacoustic and photothermal performance, high photostability, proper size, and low toxicity, SPNs not only show efficient cellular uptake for PAI and PTT toward U87 glioma cells but also demonstrate effective accumulation in both subcutaneous tumors and brain tumors upon intravenous injection, thereby realizing efficient PAI-guided PTT toward gliomas under NIR-II light irradiation.

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