Study of mesoporous silica nanowires as potential contrast agent for cancer diagnostics

Abstract

In the past years there has been a lack of contrast agents which would be able to emit light in near-infrared (NIR) diapason. Therefore mesoporous silica nanoparticles (MSN) have drawn up a lot of attention. With their tailored mesoporous structure and high surface area, MSNs as drug delivery systems (DDSs) show significant advantages over traditional drug nanocarriers.[1] They are widely studied and are promising biodegradable and biocompatible agents for potential applications in cancer diagnostics. This high interest is motivated by unique advantages of silica nanoparticles as multimodal labels for cancer diagnostics both in vitro and in vivo.[2] The aim of our study was to investigate optical properties and colloidal stability of fluorescent mesoporous silica nanoparticles. Silicon nanowires (SNW) were synthesized by process called metal-assisted chemical etching (MACE) of low boron-doped single-crystalline wafers. After the synthesis, SNW were analyzed using scanning electron microscopy (SEM) Fig. 1 (a, b). The images of SEM show, that silica nanowires are porous and elongated form. It was also observed, that silicon nanowires have strong emission in VIS-NIR spectral range under ultraviolet (UV) irradiation. In order to get colloidal solution, SNW were mechanically removed from the substrate surface. Aqueous suspensions of porous silica nanoparticles were prepared by using silica nanowires (SNW) which have been ultrasonicated for 3h in different solvents e.g. distilled water, ethanol,. Thereafter, the samples were centrifuged for 3 minutes at 2000 rpm. The resulting supernatant was used for further experiments. After centrifugation procedure supernatant was resuspended in distilled water for further investigations. Emission spectra of prepared silica nanoparticle were registered using “Cary 50”, Varian spectrophotometer. As it is presented in Fig. 1 (d), the obtained emission spectra had wide band with the peak at 655 nm. Such wide emission spectrum is associated with surface defects on silica nanoparticles and different porosity. Later on, optical stability of prepared colloidal solutions was studied. The graphs in Fig. 1 (d) show that silica nanoparticles emission intensity decay over time. It indicates that prepared colloidal silica nanoparticles are unstable in aqueous solution and require additional surface modification. As another results show, suspension made with ethanol had higher stability and bigger emission intensity than compared with the one made with distilled water.