Highly photoluminescent carbon dots with a PL quantum yield of 26% have been prepared in one step by hydrothermal treatment of orange juice. Due to high photostability and low toxicity these carbon dots are demonstrated as excellent probes in cellular imaging.

A new approach towards the design of folic acid conjugated magnetic nanoparticles for enhancing their site specific intracellular uptake against a folate receptor overexpressing cancer cells is reported. Magnetite nanoparticles were prepared by coprecipitation from an Fe3+ and Fe2+ solution followed by surface modification with 2-carboxyethyl phosphonic acid to form carboxyl group terminated nanoparticles. Then folic acid and fluorescein isothiocyanate (FITC) were conjugated with carboxylic acid functionalized magnetite nanoparticles using 2,2′-(ethylenedioxy)-bis-ethylamine. These folate-conjugated nanoparticles were characterized in terms of their size by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Surface functional groups and surface composition were analyzed by Fourier transform infrared (FTIR) spectroscopy and x-ray photoelectron spectroscopy (XPS), respectively. Vibration sample magnetometry (VSM) measurements showed the superparamagnetic nature of the particles at room temperature. Folate-conjugated magnetic nanoparticles are noncytotoxic and receptor mediated internalization by HeLa and B16 melanoma F0 cancer cells was confirmed by flow cytometry and confocal microscopy.

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A nitrogen and sulphur co-doped carbon dot (NSCD) based highly selective photoluminescent probe for mercury detection has been designed. The NSCDs with a PL quantum yield of 69% are easily prepared from a single polymeric molecular precursor. The turn on-off fluorescence change upon mercury addition is attributed to the nonradiative electron transfer from the excited state to the d-orbital of the metal ion. The soft-soft acid-base interaction between the sulphur part of the NSCD and Hg(2+) makes the fluorescence probe more specific and selective towards Hg(2+) in contrast to other metal ions. The limit of detection of mercury ions is found to be 0.05 nM. Due to their high photostability, low toxicity and low detection limit, these carbon dots are demonstrated to be excellent probes for the detection of Hg(2+) in the living cell.

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