Surface modification of CdSe-ZnS quantum dots with phospholipid from oil-seed camellia Camellia oleifera Abel.

In this work, we studied the preparation of water-dispersible fluorescent CdSe-ZnS core-shell quantum dots (QDs) using the surface modification with natural amphiphilic phospholipids (PLs) and investigated the stability and cytotoxicity of the results QDs. We isolated the amphiphilic phospholipids from extra virgin camellia (Camellia oleifera Abel.) oil by degumming process using acid treatment with 85% phosphoric acid. The results showed that the highest percent yield of the camellia phospholipids was 1.69% w/w of total extra virgin of camellia oil. The functional groups of camellia phospholipids comprised C-H bonding, carbonyl group(C=O), and PO2 as characterized by Fourier transform infrared spectroscopy, Proton nuclear magnetic resonance spectroscopy (1H-NMR) and 31-Phosphorus Nuclear magnetic resonance spectroscopy (31P-NMR). The structures of camellia phospholipids were similar to the corresponding triglyceride and mainly comprised the phosphatidylcholine and lysophosphatidylethanolamine. Furthermore, we synthesized the trioctylphophine oxide-coated CdSe-ZnS QDs (TOPO-CdSe-ZnS QDs) of different sizes by hot rapid injection including green-emitting QDs (2.67 nm), orange-emitting QDs (3.34 nm) and red-emitting QDs (4.48 nm) Before modification, the original TOPO-CdSe-ZnS QDs in hexane exhibited high quantum yield of 33.44% for green QDs, 24.9% for orange QDs and 33.36% for red QDs with the highest emission wavelength at 560, 578, and 628 nm, respectively. Then, the original QDs of different sizes were modified with camellia phospholipids through micelle formation. After modification with camellia phospholipids, the PLs-coated CdSe-ZnS QDs in 1 M Tris pH 10 exhibited the quantum yield of 2.84% for PLs-green QDs, 1.30% for PLs-orange QDs, and 2.43% for PLs-red QDs with the maximum emission peaks at 566 nm, 585 nm, and 631 nm, respectively. Moreover, The PLs-coated CdSe-ZnS QDs of three sizes in media retained the absorption spectra and unchanged in shapes, and the PLs-coated CdSe-ZnS QDs were dispersible and stable in aqueous media when compared with the TOPO-CdSe-ZnS QDs.  For cytotoxicity test, the PLs-coated CdSe-ZnS QDs showed higher cell viability than the original TOPO-CdSe-ZnS QDs at high concentrations of 1mg/ml. For cytokine detection, the original TOPO-CdSe-ZnS QDs and the PLs-coated CdSe-ZnS QDs of three sizes induce the release in TNF-α and IL-6, but not IL-1β after 24 h incubation in 264.7 raw cell. From the results, we could use the byproducts from plant edible oil production such as phospholipids in the preparation of water-dispersible quantum dots, leading to reduction in toxic chemicals used and QDs with low toxicity in vitro. The obtained water-dispersible quantum dots were potentially useful for biological applications as alternative fluorescent markers and sensors.