Porous silicon (pSi) is a sponge-like material produced by electrochemical etching of crystalline silicon wafer. It is proved to be photoluminescent (PL) due to quantum confinement effect and this is fundamental for bioimaging applications. The pSi particles gained a lot of interest in biomedicine because they are inert, biodegradable, biocompatible and have no immune response. One of the main issues of pSi particles for biomedicine applications is the fast quenching of the optical properties in biological solutions. We previously demonstrated long-term optical stability by covalent attachment of polymers such as chitosan. In this work, we demonstrate the optical stability of pSi particles in a biological buffer (e.g. PBS) by depositing an inorganic TiO2 coating by Atomic Layer Deposition (ALD) in a rotary reactor. The ALD method results in the deposition of a uniform coating on the particles and enables a fine tuning of its thickness. We investigated how the Ti precursor (TDMAT) and water vapour exposure time during ALD affect the optical properties of the pSi-TiO2 particles in biological buffer. By optimizing the ALD parameters, the PL of pSi particles stabilized more than three months (up to now) without significant effect on the morphology. Quantum yield determination gave similar result for coated and uncoated particles. In-vitro tests were performed to investigate whether the pSi-TiO2 particles affect the viability or the functional activity of human immune cells, as it was done for pSi particles without any coating. We found that TiO2 coated particles in concentration up to 100 µg/mL did not exert toxic effects on human monocytes, lymphocytes and dendritic cells. We then performed ELISA tests to evaluate whether TiO2-pSi particles activate human dendritic cells inducing the release of the immunomodulatory cytokines IL-6 and TNF-alpha. For this purpose, dendritic cells were incubated with various TiO2 coated pSi particle concentrations, as well as with the well-known bacterial immune cells activator lipopolysaccharide (LPS), as a positive control. Preliminary results indicate that coated particles induce no or weak dendritic cell activation, but could potentiate the cytokine release induced by LPS (priming effect). Our results suggest that TiO2 coated pSi particles are not harmful for human cells, but their ability to increase the immune cell activation by other agonists must be taken into account for medical purposes. This result combined to the proved photoluminescence stability in biological buffers opens the way for them to be a promising material in NanoMedicine.
|Titolo:||TiO2 coating of luminescent porous silicon by ALD technique for biomedical applications|
|Data di pubblicazione:||2017|
|Appare nelle tipologie:||04.02 Abstract in Atti di convegno|