There has been significant recent interest in the development of highly fluorescent nanomaterials as contrast agents for optical imaging in vivo. 1 The imaging agents should ideally be bright, nontoxic, biocompatible, and stable against photobleaching. Among the extensively studied are those based on semiconductor quantum dots (QDs) such as CdSe/ZnS. 2 The rationale for the use of QDs over conventional organic dyes is now generally accepted in the literature. 3 There are already successful in vivo imaging demonstrations of QDs on tumor vasculature, tumor-specific membrane antigens, sentinel lymph nodes, etc. 2,4 The semiconductor QDs containing cadmium or other heavy metals are unfortunately known for their significant toxicity even at relatively low concentrations, 5,6 which may prove prohibitive to any patient studies. Therefore, the search for benign alternatives has continued. Of particular interest and significance was the recent finding that small carbon nanoparticles could be surface-passivated by organic or bio-molecules to become strongly fluorescent. 7 These fluorescent carbon nanoparticles, 7,8 dubbed "carbon dots" (C-Dots, Scheme 1), were found to be physicochemically and photochemically stable and non-blinking. The carbon particle core could also be doped with an inorganic salt such as ZnS before the surface functionalization to significantly enhance the fluorescence brightness (C ZnS -Dots, Scheme 1). 9 These carbon dots have been successfully used for in vitro cell imaging with both one-and two-photon excitations. 7,9,10 Carbon is hardly considered as an intrinsically toxic element. Available results from the ongoing toxicity evaluation of the oligomeric PEG-functionalized C-Dots 7 in mice have suggested no meaningful toxic effects, 11 raising the prospect for in vivo biocompatibility and uses of carbon dots. Here we report the first study of carbon dots for optical imaging in vivo. The results suggest that the carbon dots are not only brightly fluorescent in solution, as reported previously, 7,9 but also well-behaved as contrast agents in live mice.The C-Dots and C ZnS -Dots with the PEG diamine, H 2 NCH 2 (CH 2 CH 2 O) n CH 2 CH 2 CH 2 NH 2 (n ∼ 35, PEG 1500N ), as the surface passivation agent were prepared and characterized as previously reported. 7,9,10 Shown in Figure 1 For subcutaneous injection, female DBA/1 mice (∼25 g) were shaved in the back area surrounding the injection point. Upon the injection of a C-Dots solution (30 µg carbon coreequivalent in 30 µL) or a C ZnS -Dots solution (65 µg in 30 µL), the mice were imagined in a Lumazone FA in vivo Imaging System (MAG Biosystems) with 470 nm (FWHM ∼ 40 nm) excitation and 525 nm (FWHM ∼ 47 nm) emission filters. As shown in Figure 2, the fluorescence images of the subcutaneously injected mice exhibited bright emissions from CDots and C ZnS -Dots. The relatively stronger fluorescence from the latter is consistent with the previously reported solution-phase results. 9 The injected carbon dots in mice diffused relatively slowly, with the ...

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Fluorescent carbon dots (small carbon nanoparticles with the surface passivated by oligomeric PEG molecules) were evaluated for their cytotoxicity and in vivo toxicity and also for their optical imaging performance in reference to that of the commercially supplied CdSe/ZnS quantum dots. The results suggested that the carbon dots were biocompatible, and their performance as fluorescence imaging agents was competitive. The implication to the use of carbon dots for in vitro and in vivo applications is discussed.

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Quantum of solace: Fluorescent carbon dots (surface‐passivated carbon nanoparticles) are developed as an alternative to classical semiconductor quantum dots. Gel column chromatography afforded carbon dots with emission yields close to 60 %. Their optical properties resemble band‐gap transitions found in nanoscale semiconductors, thus suggesting that nanoscale carbon particles acquire essentially semiconductorlike characteristics.

Graphene oxide (GO) is a highly effective absorbent of methylene blue (MB) and can be used to remove MB from aqueous solution. A huge absorption capacity of 714 mg/g is observed. At initial MB concentrations lower than 250 mg/L, the removal efficiency is higher than 99% and the solution can be decolorized to nearly colorless. The removal process is fast and more efficient at lower temperatures and higher pH values. The increase of ionic strength and the presence of dissolved organic matter would further enhance the removal process when MB concentration is high. The results indicate that GO can be applied in treating industrial effluent and contaminated natural water. The implications to graphene-based environmental technologies are discussed.

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