Zinc (II) phthalocyanine (ZnPc) is a promising photosensitizer for PDT but suffers from aggregation in physiologic aqueous environment. In this paper, a type of biocompatible polymeric nanoparticles (NPs) was prepared to encapsulate ZnPc molecules. Mostly because of the planar structure, ZnPc molecules were difficult to be encapsulated into the polymeric NPs unless further coated with a thick poly-L-lysine (PLL) layer. The PLL shell endowed the NPs good biocompatibility, efficient cellular uptake, and potential bioconjugation. The degree of aggregation (DOA) of ZnPc molecules in PLL-NPs was thoroughly investigated based on self-defined relative DOA, and a loading capacity of 4 wt % was deduced as the turning point for the aggravating of aggregation. Similarly, the optimal loading capacity of ZnPc was determined to be 4 % according to 1 O 2 generation rate, demonstrating the feasibility of DOA approach. Polymers with large rigid units (PVK and PFO) were also utilized to relieve the aggregation of ZnPc in NPs. Taking advantage of the optimized ZnPc-loaded NPs, high PDT efficacy was demonstrated on HepG2 cells and in tumor-bearing mice as well. The high in vitro and in vivo PDT efficacy and biocompatibility are both demonstrated. Aside from affording a type of efficient biocompatible nanophotosensitzes, this work is also instructive to the design of other types of ZnPc-based nanocarriers, in which aggregation should be well considered.

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