Commercial QDs are cytotoxic? There is no general consensus about toxicity, but the fear of toxicity has prevented the large use od QDs in the living tissue. Moreover:
-QDs are expensive.
-QDs agglomerate in the living cells.
-QDs cannot diffuse thru the cells membrane.
-Making QDs hydrophilic decreases stability and Quantum Yield.
Silicon QDs could be a viable solution.
-Si is cheap.
-Si is biocompatible (as demonstrated in the hydroxyapatite growth).
-Si chemistry is very well known.
-Si luminescent nanostructures are easy to produce.
-Si can be made hydrophilic by oxidation (this is not detrimental to Quantum Yield).
An easy way to produce QDs is by ultrasonic treatments of electrochemically etched Porous Silicon. We have developed this technology thanks to a special support from Regione Piemonte. The image below shows the typical structure of PS and the size distribution od interconnected crystallites.
The TEM micrograph shows the typical dimension of Si QDs. The diffraction pattern and Fourier analysis confirm that Si QDs, obtained by sonication are still crystalline.
But, what is the effect of sonication time?
This nice picture shows that sonication time tends to blue-shift the QDs emission. This can be due to a progressive erosion of the nanoparticles.
The question is if such erosion can induce defects able to kill the photoluminescence. In some cases, this can happen, in other cases, the PL abruptly shifts towards the blue-green region, indicative of a change of the emission mechanism. It is possible that the Quantum Confinement mechanism is replaced by other radiative recombination pathways, e.g. defects at the Si-SiO2 interface.
In the picture case, we have added some Undecene in the sonication bath. Undecene reveals effective in the defects passivation allowing for a progressive blue shift of the emission spectrum
|Realizzato con||::: da Otto srl|