Surface chemical modification to control molecular interactions with porous silicon

Interactions between porous silicon (pSi) particles and probe molecules were evaluated to determine the effect of pSi and probe molecule chemistry on adsorption. Methylene blue, ethyl violet and orange G dyes were chosen for investigation as they possess distinct functionalities and charges. Several distinct pSi surface species were produced via thermal oxidation at 200–800 °C and their effect on adsorption investigated. The adsorption mechanisms were elucidated from equilibrium adsorption and desorption isotherms. Methylene blue adsorption was attributed to electrostatic attraction where a gradual increase in adsorption with oxidation temperature was observed. Significant methylene blue desorption was observed at pH 3, confirming adsorption occurs via electrostatic attraction. Ethyl violet demonstrated an increase in plateau adsorption capacity and affinity with increased oxidation temperatures and adsorption was initially attributed to electrostatic attraction, however desorption of ethyl violet was not observed, thus indicating potential chemisorption. Orange G exhibited high affinity adsorption for SiySiHx terminated surfaces but no orange G desorption was detected, indicating a chemisorption adsorption mechanism. It has been successfully demonstrated that the surface modification of pSi enabled the manipulation of molecular interactions. By interacting probe molecules with similar functionalities to drug molecule with pSi, greater understanding of drug-pSi interactions can be ascertained which are of great importance. pSi surface chemistry can be tailored to enable control over molecular interactions and ultimately dictate loading, encapsulation and release behavior.

Effect of pH on methylene blue desorption from unoxidized (◊) and 800 °C (o) oxidized porous silicon particles.Figure optionsDownload high-quality image (72 K)Download as PowerPoint slideHighlights
► Dye adsorption onto unoxidized and thermally oxidized porous silicon.
► Porous silicon oxidation temperature controls dye mass adsorbed.
► Adsorption mechanism dependent on dye chemistry.
► Electrostatic attraction and chemisorption mechanisms observed.
► Desorption of dye adsorbed via electrostatic attraction but not chemisorption.