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.Since the preparation method of silica nanoparticles was developed by Werner Stöber, 1 many researchers have focused on attempts to control the size and uniformity, as well as to utilize them to various fields including biological application. Silica has several advantages including its ease of preparation through the hydrolysis-condensation reaction from relatively inexpensive precursor molecules such as tetraethyl orthosilicate (TEOS) in the presence of acid-or base-catalysts, the possibility of surface modification with various well-studied organosilicon compounds,2 and its non-acute toxicity.3a,b As the surface silanol groups can be easily modified by various functional groups and modified silica nanoparticles can effectively penetrate the cell membrane, there has been a great amount of research effort to use them as carriers for the delivery of drugs or genes.3a,c,d , 4 To improve the application of silica nanoparticles to biological research, fluorescent dye molecules were introduced into silica nanoparticles by using a thiourea-linkage forming reaction through amino-terminated alkyltrialkoxysilane compounds such as (3-aminopropyl)triethoxysilane (APS) and dye molecules having an isothiocyanate functional group, i.e. Rhodamine isothiocyanate (RITC) and Fluorescein isothiocyanate (FITC).5 This photostable fluorescent property has become one of the most appreciated functionalities of fluorescent silica nanoparticles and has opened a new era of bioimaging.6 -8a Although this thiourea-linkage formation reaction is simple and well studied as a useful bioconjugation method,9 it has several drawbacks in preparing fluorescent silica nanoparticles. First, an excess amount of APS is usually used in order to incorporate all the possible dye molecules into silica nanoparticles (about two times excess compared to the amount of isothiocyanated dye molecule such as RITC or FITC), and it is cocondensed with TEOS during the silica formation process. Although the amino terminal groups on the nanoparticle surface could be used for the further chemical linkage reactions such as conjugation with drugs or specific binding antibodies,8b,d the amount of amino terminal groups was not reproducibly controllable and the excess amount of APS sometimes adversely NIH Public Access Author ManuscriptChem Commun (Camb). Author manuscript; available in PMC 2010 June 1. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript affected the size uniformity.10a Second, it is reported that primary amine groups on the surface make silica nanoparticles stable and dispersible only in acidic condition, but lead to precipitation in neutral ...

Synthesis of pH stable, blue light-emitting diode-excited, fluorescent silica nanoparticles and effects on cell behavior

“…22,23 As such, the excess surfactants have to be removed for biological applications, or reduced cell viability will occur. 24 The emission color can be easily tuned by incorporating organic dyes, 13 inorganic complexes, 25 dye ratios, 26 or quantum dots. 27 Their excitation is necessary for emission to observe cell or organelle location or track changes in cell behavior.…”

“…20 To control the shape or size of silica nanomaterials, the concentration of TEOS, ammonia, and surfactants is varied. 13,21 The rod-like shape can be controlled by a surfactant, which directly affects cell viability and can also control porosity. 22,23 As such, the excess surfactants have to be removed for biological applications, or reduced cell viability will occur.…”

“…28 Finally, hydrosilylation was conducted under platinum catalyst with quantitative yield (Scheme 1B). 13 The dye was obtained with an overall high yield of 56%. The hydrosilylated, NI-3 has six reactive methoxysilane groups.…”

“…All chemicals were used without further purification. The NI derivatives were characterized by 1 H and 13 C NMR (500 MHz; Varian, Palo Alto, CA, USA) and mass spectrometer (JMS-AX505WA; JEOL, Tokyo, Japan). Photophysical properties were obtained by UV-visible spectrometer (S-3100; Scinco, Seoul, South Korea), fluorescence spectrophotometer (FP-6500; Jasco, Oklahoma City, OK, USA), and absolute QY system (C9920-02; Hamamatsu Photonics, Hamamatsu, Japan).…”

“…13,29 To confirm the relationship between ammonia concentration and size, we varied the concentration of 14% ammonia from 8 to 16 mL under the same concentration of dye. For every 0.2 mM (14 mg) of the dye, the size is increased from 50 to 120 nm (#3, #5, and #6 in Table 1).…”