A nano complex of hydrophilic phthalocyanine and polyethylenimine for improved cellular internalization efficiency and phototoxicity

To enhance the cellular internalization and phototoxicity of sulfonated aluminum phthalocyanine (AlPcS), a hydrophilic photosensitizer (PS), nano complexes composed of a mixture of AlPcS (negatively charged) and polyethylenimine (PEI; positively charged) with different weight ratios of PEI to AlPcS were prepared via electrostatic interaction. The size of the PEI/AlPcS 0.6 (weight ratio = PEI/AlPcS) was below 200 nm with a monodispersed size distribution. The cellular uptake of the complex was determined using a fluorescence image test, a cell lysis test and confocal observation. The cellular internalization of AlPcS in the PEI/AlPcS 0.6 nano complex was 87 times higher than that of free AlPcS after 6 h. The photoactivity of the nano complex, as measured by fluorescence intensity and singlet oxygen generation activity in PBS buffer, was completely eliminated by a self-quenching effect. After cellular uptake, the loss of the fluorescence intensity was restored by the dissociation of the nano complex. Additionally, the phototoxicity of the complex, both with and without light irradiation, was investigated using an MTT colorimetric assay. Although the free AlPcS did not exhibit phototoxicity, the nano complex showed strong phototoxicity after irradiation. Therefore, we suggest that the nano complex system has potential use in clinical photodynamic therapy and in the biological study of various cancers.