Conversion of purpurin 18 to chlorin P6 in the presence of silica, liposome and polymeric nanoparticles: A spectroscopic study

Effect of nanoparticle (NP) environment on the conversion of entrapped photosensitizer purpurin 18 (Pp18) to chlorin p6 (Cp6) was studied spectroscopically. This was investigated by monitoring the time dependent absorption and emission kinetics of the Pp18 entrapped in four different NPs suspended in buffer at physiological pH in the presence and absence of serum up to 24 h. These were organically modified silica NP (SiNP) having vinyl and/or amino propyl groups, poly-lactic-co-glycolic acid (PLGA) NP and liposome. The results of the spectroscopic studies reveal that Pp18 is least converted to Cp6 (i.e., most stable) in the SiNP having vinyl groups whereas its conversion is fastest in PC liposome. In the presence of serum proteins, although the conversion is enhanced, the trend remains similar. Our investigation suggests that SiNP having vinyl functional groups might be a better carrier of Pp18 at physiological pH.