Two-Photon Cerebrovascular and Thrombus Fluorescence Imaging with Micrometer-Scale Penetration Depth Using Record-Low-Dose Aggregation-Induced Emission Nanoprobes

Two-photon fluorescence imaging, which utilizes near-infrared light to achieve 3D tomography of deep tissues, has rapidly advanced in brain vascular research. The demand for high-resolution images with minimal side effects has recently driven significant attention toward the development of two-photon fluorescence probes. In this contribution, through a cascade strategy of precise molecular structure optimization and nanoengineering, a TTNB SiO₂-shelled aggregation-induced emission (AIE) nanoprobe (NP) is developed to show high two-photon absorption cross-section and near-infrared emission with a high quantum yield (QY) of 69%. Importantly, it also shows neglected photosensitization and photothermal effects for minimizing the side effects during the imaging process. Transient absorption spectroscopy (TAS) results and theoretical modeling indicated that isolating the TTNB molecule from water and oxygen by the SiO₂ shell is crucial for decreasing the photosensitization and photothermal effects and also promoting the delayed fluorescence to enhance the QY of the nanoprobe. Consequently, deep-tissue 3D mouse cerebral vascular imaging with micrometer-scale penetration depth is realized by using only 1 mg/kg of the probe, which is the record low dose under the same imaging quality. Meanwhile, it is also used for further investigation into the hemodynamic changes during cerebral thrombosis.