Surface charge of well-defined polymeric nano-stars regulates non-invasive fluorescence imaging of lymph node

Accurate identification of sentinel lymph node (SLN) is crucial for clinical SLN biopsy surgery. Herein, we developed an innovative nanoprobe based on well-defined core crosslinked star (CCS) polymers for non-invasive fluorescence imaging of SLN. A well-defined biodegradable CCS polymer comprising multiple polyethylene glycol (PEG) arms and carboxyl terminal groups (denoted as CCS-COOH) was synthesized successfully by reversible addition-fragmentation chain transfer polymerization with a disulfide-based crosslinker reagent. Besides, CCS-COOH was coupled by tert-butyl carbazate to produce the CCS derivative with neutral butoxycarbonyl (Boc) terminal groups (denoted as CCS-Boc). By the removal of Boc groups, another CCS derivative with positive primary amino terminal groups (denoted as CCS-NH₂) was also yielded. These CCS polymers had similar particle size but different surface charge. For SLN fluorescence imaging, the CCS polymers labeled by CY7, a near-infrared probe, exhibited superior in vitro photo-stability to CY7 alone. After intradermal injection of the CY7-labeled CCS polymers in a mouse model, they could efficiently accumulate in the lymph node of the mouse. CY7-labeled CCS-COOH having negatively-charged surface displayed longer duration time and higher fluorescence intensity in the lymph node as compared to its counterparts with neutral or positive charge surface. In vitro and in vivo toxicity tests supported low cytotoxicity of these CCS polymers against cell lines and low systemic toxicity. The results of this work highlight the potential of negatively-charged near-infrared-emitting CCS polymer as a new nanoprobe for safe and efficient SLN imaging.