Precise Deciphering of Brain Vasculatures and Microscopic Tumors with Dual NIR‐II Fluorescence and Photoacoustic Imaging

Diagnostics of cerebrovascular structures and microscopic tumors with intact blood-brain barrier (BBB) significantly contributes to timely treatment of patients bearing neurological diseases. Dual NIR-II fluorescence and photoacoustic imaging (PAI) is expected to offer powerful strength, including good spatiotemporal resolution, deep penetration, and large signal-to-background ratio (SBR) for precise brain diagnostics. Herein, biocompatible and photostable conjugated polymer nanoparticles (CP NPs) are reported for dual-modality brain imaging in the NIR-II window. Uniform CP NPs with a size of 50 nm are fabricated from microfluidics devices, which show an emission peak at 1156 nm with a large absorptivity of 35.2 L g^-1 cm^-1 at 1000 nm. The NIR-II fluorescence imaging resolves hemodynamics and cerebral vasculatures with a spatial resolution of 23 µm at a depth of 600 µm. The NIR-II PAI enables successful noninvasive mapping of deep microscopic brain tumors (<2 mm at a depth of 2.4 mm beneath dense skull and scalp) with an SBR of 7.2 after focused ultrasound-induced BBB opening. This study demonstrates that CP NPs are promising contrast agents for brain diagnostics.