Cytosolic protein delivery <i>via</i> protein-bound microparticles based on anionic boron clusters and cationic polymers

Direct protein delivery to the cytosol facilitates immediate functional expression of proteins without the risks associated with gene introduction. However, the technology for delivering various proteins to the cytosol is still in its infancy. Herein, the formation of microparticles comprising anionic boron clusters and the cationic polymer hexadimethrine bromide (HDB) is demonstrated. In particular, the microparticles formed from dodecabromododecaborate clusters and HDB are confirmed to be bound with proteins. The protein-bound boron cluster/polymer-based microparticles (protein·BPMs) are internalized into cells <i>via</i> endocytosis. Upon internalization, the protein·BPMs release the proteins with different isoelectric points and sizes into the cytosol. Furthermore, an enzyme is delivered by protein·BPMs into the cytosol of various cell types while maintaining its functional activity. This method, owing to the simple preparation of protein·BPMs, represents a promising approach for delivering diverse proteins to various cell types. Our findings open new avenues for utilizing boron clusters in cytosolic delivery systems.