Semiconductor quantum dots (QDs) hold some advantages over conventional organic fluorescent dyes. Due to these advantages, they are becoming increasingly popular in the field of bioimaging. However, recent work suggests that cadmium based QDs affect cellular activity. As a substitute for cadmium based QDs, we have developed photoluminescent stable silicon quantum dots (Si-QDs) with a passive-oxidation technique. Si-QDs (size: 6.5 ± 1.5 nm) emit green light, and they have been used as biological labels for living cell imaging. In order to determine the minimum concentration for cytotoxicity, we investigated the response of HeLa cells. We have shown that the toxicity of Si-QDs was not observed at 112 µg ml(-1) and that Si-QDs were less toxic than CdSe-QDs at high concentration in mitochondrial assays and with lactate dehydrogenase (LDH) assays. Especially under UV exposure, Si-QDs were more than ten times safer than CdSe-QDs. We suggest that one mechanism for the cytotoxicity is that Si-QDs can generate oxygen radicals and these radicals are associated with membrane damages. This work has demonstrated the suitability of Si-QDs for bioimaging in lower concentration, and their cytotoxicity and one toxicity mechanism at high concentration.
Cytotoxicity of human cervical carcinoma cell line (HeLa cells) labeled with the nanocrystalline silicon (nc-Si) particles before and after ultraviolet (UV) light exposure has studied on the viability and cellular membrane damages. The viability and cellular membrane damages of HeLa cells changed at high particle concentration of 1.12 mg/ml. The viability of HeLa cells labeled with the UV-exposed nc-Si particles was higher than that of unexposed nc-Si particles. However, the variation of cellular membrane damages was almost same for the nc-Si particles before and after UV exposure. These results substantiated the low toxicity of nc-Si particles. Moreover, the HeLa cells labeled with the nc-Si particles exhibited green fluorescence. On the other hand,in vivotest of nc-Si particles estimated by the visualization observation of the circulation from the lymphatic vessel to the lymph node of a mouse. The transfer pathway of nc-Si particles could be clearly monitored by the strong emission of red light.
Quantum dots (QDs) have brighter and longer fluorescence than organic dyes. Therefore, QDs can be applied to biotechnology, and have capability to be applied to clinical technology. Currently, among the several types of QDs, CdSe with a ZnS shell is one of the most popular QDs to be used in biological experiments. However, when the CdSe-QDs were applied to clinical technology, potential toxicological problems of CdSe core should be considered. To overcome the problem, silicon nanocrystals, which have the potential of biocompatibility, could be a candidate of alternate probes.Silicon nanoparticles have been synthesized using several techniques. Recently, novel silicon nanoparticles were reported to be synthesized with the combination methods, radio frequency sputtering method and hydrofluoric-etching method In order to assess the biocompatibility of the Silicon nanoparticles, we performed two different cytotoxicity assays, cell viability/proliferation assay using the mitochondrial activity assay and cell membrane damage assay using the lactate dehydrogenase assay.At the 112 µ g/mL of silicon nanoparticles (the maximum concentration in this study), we could detected the cell membrane damage of HeLa cells and the decrease of hepatocytes viability. We concluded that we could use the silicon nanoparticles as bioimaging marker but the attention should be given when Silicon nanoparticles were applied to cells in high concentration.
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