Rapid conjugation of nanoparticles, proteins and siRNAs to microbubbles by strain-promoted click chemistry for ultrasound imaging and drug delivery.

A new strategy using catalyst-free strain-promoted alkyne-azide cycloaddition (SPAAC) "click" chemistry for the ligation of anti-cancer drug-loaded nanoparticles, functionalized proteins, and siRNA conjugated micelles to microbubbles (MB) was established. The results showed fast ligation within 5 min without sacrificing microbubble size and density. The ultrasound test showed good imaging abilities of the microbubbles after functionalization. This microbubble-therapeutic SPAAC "click" conjugation developed in the current study involves no toxic catalyst or initiator, has ultra-fast reaction speed, and is versatile for the ligation of various anti-cancer or therapeutic agents to microbubbles. These advantages render the SPAAC click strategy promising for broad applications in ultrasound-guided imaging and therapeutic delivery.