Surface functionalization of highly luminescent carbon nanodots from Dioscorea hispida with polyethylene glycol and branched polyethyleneimine and their in vitro study

Synthesized carbon dots (C-dots) from Dioscorea hispida (Gadong tuber) starch were modified with passivating agents such as O,O-bis(3-aminopropyl)polyethylene glycol 1500 (PEG(1500N)) and branched polyethyleneimine (BPEI) to increase the functional efficiency of C-dots to be used in biological investigations. After surface modification, the C-dots decreased in size from 6-25 to 3-20 nm without changing their morphology. The modified C-dots were fluorescent, and the fluorescence peak gradually shifted to a longer excitation wavelength (from 420 to 500). Upon modification, thereby elucidating a competitive quantum yield of 15% (C-dots-PEG(1500N)) and 12.6% (C-dots-BPEI). The UV-visible spectrum of the C-dots modified with PEG(1500N) contained an absorption peak at 290 nm, whereas, that of the C-dots modified with BPEI contained peak at 360. Fourier-transform infrared analysis showed a peak at 1700 cm(-1) (C-dots-PEG(1500N)) and 1697 cm(-1) (C-dots-BPEI) that corresponds to the amide (-HCONH-) carbonyl bond, indicating that PEG(1500N) and BPEI had been successfully passivated on the surface of C-dots. To examine photothermal response, irradiation was carried out for 5 min using three different instruments which is UV-lamp (365 nm), visible lamp and laser (532 nm, 1 W/cm(2)) where temperature for each sample increased respectively. C-dots demonstrated not losing their luminescent properties upon irradiation to UV-lamp and laser for 30 min. Contrary, the intensity of fluorescence reduced when it exposed to the visible lamp for the same period. In vitro studies of the modified C-dots with zebrafish (Danio rerio) revealed that C-dots-PEG(1500N) is non-toxic while C-dots-BPEI is highly toxic to the fish embryos. Significantly, this study has successfully demonstrated that Gadong tuber starch can be used as a starch-based modifier for C-dots; which possibly can be utilized as a nanocarrier with thermal sensing properties. (C) 2018 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University.