Amine Surface Modifications and Fluorescent Labeling of Thermally Stabilized Mesoporous Silicon Nanoparticles

Mesoporous silicon (PSi) has been shown to have extensive application opportunities in biomedicine, whereas it has frequently failed to produce complex systems based on PSi due to the lack of surface functional groups or the instability of the unmodified PSi surface. In the present study, PSi nanoparticles, stabilized by thermal oxidation or thermal carbonization, were successfully modified by grafting aminosilanes on the surface. The modifications were performed by covalently bonding 3-triethoxysilylpropyl-amine (APTES) or 3-(2-aminoethylamino) propyldimethoxymethylsilane (AEAPMS) on thermally oxidized PSi (TOPSi) and thermally carbonized PSi (TCPSi). These materials were systematically characterized with N-2 ad/desorption, TEM, contact angle, zeta potential, FT-IR, Si-29 CP/MAS NMR, and elemental analysis. To evaluate their application potentials, a fluorescent dye, fluorescein 5-isothiocyanate (FITC), was coupled on the surface of amine-modified nanoparticles. The effects of PSi matrix and surface amino groups on FITC coupling efficiency, fluorescent intensity, and the stability of fluorescence in simulated body fluid (SBF) were investigated. The nanoparticles modified with AEAPMS had higher FITC coupling efficiency than those modified with APTES. FITC-coupled TOPSi nanoparticles also possessed brighter fluorescence and better fluorescent stability in OF. Furthermore, due to the protection caused by the mesoporous structure of PSi nanoparticles, the FITC-coupled TOPSi nanoparticles showed superior photostability in photobleaching experiment.