Hybrid silica nanoparticles traceable by fluorescence and FT-IR spectroscopy: preparation, characterization and preliminary biological studies

The novel reporters, unimodal FT-IR-traceable, bimodal fluorescent and FT-IR-traceable hybrid silica (SiO2) nanoparticles (NPs), were prepared using the Stober methodology. Initially, the basic Stober cohydrolysis of tetraethoxysilane (TEOS) and of the iron-complexed alkyl-triethoxysilane (EtO)(3)Si-L-(eta(4)-2E, 4E-dienyl)-Fe(CO)(3)(0) (L = alkyl linker, DIT-tag reagent 3) afforded unimodal 13.7 +/- 2 nm-sized SiO2@DIT-tag(60) NPs. These NPs can incorporate an organometallic FT-IR sensitive (eta(4)-2E, 4E-dienyl)-tricarbonyliron(0) complex moiety which acts as a sensitive FT-IR traceable species due to the strong iron complex nu(FeC)equivalent to O vibrational bands that appear in the 1996-2063 cm(-1) region, a region free of any parasitic band. The sensitivity of the FT-IR-based detection of SiO2@DIT-tag(60) NPs has been determined using incremental mixtures of B16 melanoma cell lysates as a biological medium model. The detection limit was found to be 0.190 mu g of Fe per mg of B16 cell lysate. In the second step, bimodal hybrid fluorescent and FT-IR-traceable 35.7 +/- 5 nm sized SiO2@DIT-tag(20)@FITC NPs were similarly fabricated, in order to enable both fluorescence and FT-IR spectroscopy detection. This has been readily obtained through the straightforward co-incorporation of an additional fluorescein-containing alkyl-triethoxysilane conjugate FITC-APTES (FITC: fluorescein isothiocyanate, APTES: (3-aminopropyl)triethoxysilane). Subsequent surface modification with APTES of the resulting SiO2@DIT-tag(20)@FITC NPs afforded amine functionalized 34.4 +/- 6 nm-sized SiO2@ DIT-tag(20)@FITC@NH2 NPs that were readily endocytosed by B16 melanoma cells. All these novel hybrid silica NPs have been fully characterized by FT-IR spectroscopy, high resolution TEM/SEM (HR-TEM/SEM) with elemental energy-dispersive X-ray spectroscopy (compositional EDAX analysis), dynamic light scattering (DLS), zeta potential measurements, and inductively coupled plasma-optical emission spectroscopy (ICP-OES). Preliminary biological studies demonstrated the non-toxicity of the NPs. No observable modification in the B16 cells' morphology or mortality was seen after the internalization of SiO2@DIT-tag(20)@FITC@NH2 NPs.