Surface Heterogeneous Nucleation-Mediated Release of Beta-Carotene from Porous Silicon

Abstract

We demonstrate that the release of a poorly soluble molecule from nanoporous carriers is a complex process that undergoes heterogeneous surface nucleation events even under significantly diluted release conditions, and that those events heavily affect the dynamics of release. Using beta-carotene and porous silicon as loaded molecule and carrier model, respectively, we show that the cargo easily nucleates at the pore surface during the release, forming micro- to macroscopic solid particles at the pores surface. These particles dissolve at a much slower pace, compared to the rate of dissolution of pure beta-carotene in the same solvent, and they negatively affect the reproducibility of the release experiments, possibly because their solubility depends on their size distribution. We propose to exploit this aspect to use release kinetics as a better alternative to the induction time method, and to thereby detect heterogenous nucleation during release experiments. In fact, release dynamics provide much higher sensitivity and reproducibility as they average over the entire sample surface instead of depending on statistical analysis over a small area to find clusters.

Nanoscale Silicon Oxide Reduces Electron Transfer Kinetics of Surface-Bound Ferrocene Monolayers on Silicon

“…Fundamental and applied research on the self-assembly of organic molecules on electrode surfaces continues to be an area of intense research. To date, the focus has been on the formation of self-assembled monolayers (SAMs) on gold electrodes using thiol or disulfide-terminated molecules, − but there is increasing interest of forming monolayers on a range of other electrodes. − The study by Chidsey and co-workers on Si–C-bound monolayers has helped to expand this research from metals to semiconductors. − In particular, monolayers on oxide-free silicon (Si–H) have gained significant interest because they enable combining the traditional semiconducting properties of Si with those of functional organic molecules. ,− For example, Si-based SAMs have been exploited in solar cell research, − biosensors, − fundamental electron transfer studies, − and molecular electronics. − …”