Self-Reporting Photoluminescent Porous Silicon Microparticles for Drug Delivery

A porous Si (pSi) microparticle-based delivery system is investigated, and the intrinsic luminescence from the particles is employed as a probe to monitor the release of a model protein payload, bovine serum albumin (BSA). The microparticles consist of a core Si skeleton surrounded by a SiO₂ shell. Two types of pSi are tested, one with smaller (10 nm) pores and the other with larger (20 nm) pores. The larger pore material yields a higher mass loading of BSA (3 vs 20%). Two different methods are used to load BSA into these nanostructures: the first involves loading by electrostatic physisorption, and the second involves trapping of BSA in the pSi matrix by local precipitation of magnesium silicate. Protein release from the former system is characterized by a burst release, whereas in the latter system, release is controlled by dissolution of the pSi/magnesium silicate matrix. The protein release characteristics are studied under accelerated (0.1 M aqueous KOH, 21 °C) and physiologically relevant (phosphate-buffered saline, pH 7.4, 37 °C) conditions, and the near-infrared photoluminescence signal from the pSi skeleton is monitored as a function of time and correlated with protein release and silicon dissolution. The thickness of the Si core and the SiO₂ shell are systematically varied, and it is found that the luminescence signature can be tuned to provide a signal that either scales with protein elution or that changes rapidly near the end of useful life of the delivery system. Although payload release and particle dissolution are not driven by the same mechanism, the correlations between luminescence and payload elution for the various formulations can be used to define design rules for this self-reporting delivery system.