Atomically Precise Fluorescent Gold Nanocluster as a Barrier‐Permeable and Brain‐Specific Imaging Probe.

Photonic nanomaterials play a crucial role in facilitating the necessary signal for optical brain imaging, presenting a promising avenue for early diagnosis of brain‐related disorders. However, the blood‐brain barrier (BBB) presents a significant challenge, blocking the entry of most molecules or materials from the bloodstream into the brain. To overcome this, photonic nanocrystals in the form of gold clusters (LAuC) with size less than 3 nm, have been developed, with Levodopa conjugated to LAuC (Dop@LAuC) for targeted brain imaging. Dop@LAuC crosses the BBB and emits in the near‐infrared (NIR) wavelength, enabling real‐time optical brain imaging. An <italic>in vitro</italic> BBB model using brain endothelial cells showed that 50 % of Dop@LAuC crossed the barrier within 3 hours, compared to only 10 % of LAuC, highlighting the enhanced ability of L‐dopa‐conjugated gold clusters to penetrate the BBB. <italic>In vivo</italic> optical imaging in healthy mice further confirmed the material's efficacy to cross BBB without compromising the barrier integrity. [ABSTRACT FROM AUTHOR]