New method to prepare very stable and biocompatible fluorescent silica nanoparticles

Abstract

A new synthetic method has been developed to prepare fluorescent silica nanoparticles without employing isothiocyanated dye molecules and (3-aminopropyl)triethoxysilane (APS) for the thiourea linkage formation; the resulting fluorescent silica nanoparticles show excellent photochemical, thermal and pH stabilities and a good biocompatibility with over 85% viability from various cell types.

Figure 1

Photoluminescence spectra and photographs of 50 nm-sized, dye-incorporated silica nanoparticle in water.

Figure 2

Stability of 50 nm-sized, fluorescent silica nanoparticles in water at various pH and in ethanol; (a) and (b) precipitated SiO₂ prepared by FITC-APS conjugated method, (c) and (d) dispersed SiO₂ prepared by a direct modification of fluorescein molecule as described in Scheme 1(b). Images (b) and (d) were taken under UV irradiation.

Figure 3

Fluorescent images of MC3T3-E1 cells incubated with 50 nm-sized, positively charged, orange fluorescent silica nanoparticles; 100 µg ml⁻¹ of nanoparticles were added to the medium.

Scheme 1

Derivatization of organic dyes for incorporation into silica matrices. Reagents and conditions: (i) allyl iodide, Cs₂CO₃, DMF; (ii) trimethoxysilane, Pt/C, methanol; (iii) triethoxysilane, Pt(dvs), toluene; R₁ = –CH₂–CH==CH₂, R₂ = –(CH₂)₃Si(OMe)₃, R₃ = –(CH₂)₃Si(OEt)₃