Enhanced photoacoustic effect for simultaneous imaging and drug release using phase-transition mesoporous silicon nanoprobe

Probe-assisted integration of imaging and therapy into a single modality provides tremendous opportunities in biological applications. In this study, phase-transition-mediated cavitation was used for simultaneous photoacoustic imaging (PA) and triggering drug release. For this purpose, we developed unique phase-transition mesoporous silicon nanoprobes (ICG/PFC/PTX@MSNs) consisting of indocyanine green (ICG), perfluorocarbon (PFC), and paclitaxel (PTX). For high-dose laser irradiation, the encapsulated ICG absorbs laser energy, providing localized heating well over the supercritical temperature of PFC. Then, liquid PFC was subjected to a liquid-to-gas phase transition, which generated stronger PA signals and promoted fast drug release. The enhancement of ICG/PFC/PTX@MSNs for PA imaging was demonstrated in in vitro and in vivo experiments. The average PA signal based on the phase-transition mechanism was ∼3 times higher than that of the traditionally used thermal expansion mechanism. Furthermore, the rapid drug release based on the same phase-transition-mediated cavitation mechanism can be achieved simultaneously; eventually, ∼80.4% of the total encapsulated drug were released. The hematoxylin–eosin stained section of tumor tissues from the ICG/PFC/PTX@MSN group showed many dead cells with condensed nuclei and pyknosis. This method not only promotes efficacy of chemotherapy but also makes accurate imaging-guided chemotherapy possible.