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We describe the synthesis of Gd(III)-doped carbon dots as dual fluorescence-MRI probes for biomedical applications. The derived Gd(III)-doped carbon dots show uniform particle size (3-4 nm) and gadolinium distribution and form stable dispersions in water. More importantly, they exhibit bright fluorescence, strong T1-weighted MRI contrast and low cytotoxicity.In the past several years semiconductor quantum dots have been the subject of intense research due to their scientific and technological importance. 1 Recently, carbon dots (C-dots) have emerged as environmentally friendly complements to calcogenide-based quantum dots. 2,3 The strong fluorescence and low toxicity of C-dots make them attractive materials for a variety of biomedical applications, such as biosensing and bioimaging. 2 However, the origin of fluorescence of C-dots is not completely understood. 3a Their optical behaviors can be partially explained in terms of recombination of excitons on the Cdot surface and/or by polyaromatic fluorophores originating from the preparation. 3a,4 For several applications, materials that combine fluorescence with additional functionality (e.g., magnetic response) in a single platform can be highly advantageous. To this end, we recently reported a series of magneto/fluorescent core-shell hybrids by decorating magnetic nanoparticles with C-dots. 5a Srivastava et al. also reported magnetic nanocomposites by thermal decomposition of organic precursors in the presence of Fe 3 O 4 nanoparticles. 5b Here we report the first Gd-doped C-dots that combine fluorescence with a strong MRI contrast. Sun and co-workers have reported previously Zn-doped C-dots with high photoluminescence (comparable to semiconductor quantum dots) but no reports exist for direct incorporation of various dopants especially to impart additional functionality. 6 Furthermore, the incorporation of the Gd compound into solid matrices brings extra advantages to T1 contrast enhancement in comparison to a ''free'' T1 contrast agent. The r 1 relaxivity is increased due to the slowing of tumbling of the Gd complex caused by attachment to a solid support. 7 Also, nanoparticles based on inorganic Gd compounds (i.e., Gd 2 O(CO 3 ) 2 , Gd 2 O 3 ) show a good T1 contrast enhancement. 8 However, these materials do not have high payloads of magnetic centers because of high diameters. Since our general synthesis approach is based on pyrolysis of molecular precursors, 9 dopants can be mixed in prior to the thermal treatment avoiding post-synthesis steps. The Gd-doped C-dots are uniform in size and highly dispersible in water. Moreover, in addition to their fluorescence they exhibit strong T1-weighted MRI contrast (comparable to commercial Gadovist) and low cytotoxicity. These features make them very promising candidates for biomedical applications as dual fluorescence-MRI probes. 10 The Gd-containing C-dots were synthesized by mixing gadopentetic acid into tris(hydroxymethyl)aminomethane (Tris base) and betaine hydrochloride followed by pyrolysis in air at 250 C. In th...

In this work, it is shown that the hydrophilic functionalized multiwall carbon nanotubes (MWCNs) can stabilize a large amount of pristine graphene nanosheets in pure water without the assistance of surfactants, ionic liquids, or hydrophilic polymers. Role of stabilizer is conveyed by highly hydrophilic carbon nanotubes, functionalized by dihydroxy phenyl groups, affording a stable dispersion at concentrations as high as 15 mg mL−1. Such multidimensional (2D/1D) graphene/MWCN hybrid is found to be dispersible also in other polar organic solvents such as ethanol, isopropanol, N,N‐dimethylformamide, ethylene glycol, and their mixtures. High‐resolution transmission microscopy and atomic force microscopy (AFM) including a liquid mode AFM manifest several types of interaction including trapping of multiwalled carbon nanotubes between the graphene sheets or the modification of graphene edges. Molecular dynamic simulations show that formation of an assembly is kinetically controlled. Importantly, the hybrid can be deposited on the paper by drop casting or dispersed in water‐soluble polymers resulting in record values of electrical conductivity (sheet resistance up to Rs ≈ 25 Ω sq−1 for free hybrid material and Rs ≈ 1300 Ω sq−1 for a polyvinilalcohol/hybrid composite film). Thus, these novel water dispersible carbon superstructures reveal a high application potential as conductive inks for inkjet printing or as highly conductive polymers.

Much of the research effort on graphene focuses on its use as a building block for the development of new hybrid nanostructures with well-defined dimensions and properties suitable for applications such as gas storage, heterogeneous catalysis, gas/liquid separations, nanosensing, and biomedicine. Toward this aim, here we describe a new bottom-up approach, which combines self-assembly with the Langmuir-Schaefer deposition technique to synthesize graphene-based layered hybrid materials hosting fullerene molecules within the interlayer space. Our film preparation consists in a bottom-up layer-by-layer process that proceeds via the formation of a hybrid organo-graphene oxide Langmuir film. The structure and composition of these hybrid fullerene-containing thin multilayers deposited on hydrophobic substrates were characterized by a combination of X-ray diffraction, Raman and X-ray photoelectron spectroscopies, atomic force and scanning electron microscopies, and conductivity measurements. The latter revealed that the presence of C 60 within the interlayer spacing leads to an increase in electrical conductivity of the hybrid material as compared to the organo-graphene matrix alone.

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