Similar to its popular older cousins the fullerene, the carbon nanotube, and graphene, the latest form of nanocarbon, the carbon nanodot, is inspiring intensive research efforts in its own right. These surface-passivated carbonaceous quantum dots, so-called C-dots, combine several favorable attributes of traditional semiconductor-based quantum dots (namely, size- and wavelength-dependent luminescence emission, resistance to photobleaching, ease of bioconjugation) without incurring the burden of intrinsic toxicity or elemental scarcity and without the need for stringent, intricate, tedious, costly, or inefficient preparation steps. C-dots can be produced inexpensively and on a large scale (frequently using a one-step pathway and potentially from biomass waste-derived sources) by many approaches, ranging from simple candle burning to in situ dehydration reactions to laser ablation methods. In this Review, we summarize recent advances in the synthesis and characterization of C-dots. We also speculate on their future and discuss potential developments for their use in energy conversion/storage, bioimaging, drug delivery, sensors, diagnostics, and composites.

Luminescent Carbon Nanodots: Emergent Nanolights

Department of Materials Science, University of Patras, 26504 Rio Patras, Greece, Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vass. Constantinou Avenue, 116 35 Athens, Greece, Institut de Biologie Moleculaire et Cellulaire, UPR9021 CNRS, Immunologie et Chimie Therapeutiques, 67084 Strasbourg, France, and Dipartimento di Scienze Farmaceutiche, Universita di Trieste, Piazzale Europa 1, 34127 Trieste, Italy

Chemistry of Carbon Nanotubes

Fluorescent carbon nanoparticles or carbon quantum dots (CQDs) are a new class of carbon nanomaterials that have emerged recently and have garnered much interest as potential competitors to conventional semiconductor quantum dots. In addition to their comparable optical properties, CQDs have the desired advantages of low toxicity, environmental friendliness low cost and simple synthetic routes. Moreover, surface passivation and functionalization of CQDs allow for the control of their physicochemical properties. Since their discovery, CQDs have found many applications in the fields of chemical sensing, biosensing, bioimaging, nanomedicine, photocatalysis and electrocatalysis. This article reviews the progress in the research and development of CQDs with an emphasis on their synthesis, functionalization and technical applications along with some discussion on challenges and perspectives in this exciting and promising field.

Carbon quantum dots and their applications

Suitable labels are at the core of Luminescence and fluorescence imaging and sensing. One of the most exciting, yet also controversial, advances in label technology is the emerging development of quantum dots (QDs)--inorganic nanocrystals with unique optical and chemical properties but complicated surface chemistry--as in vitro and in vivo fluorophores. Here we compare and evaluate the differences in physicochemical properties of common fluorescent labels, focusing on traditional organic dyes and QDs. Our aim is to provide a better understanding of the advantages and limitations of both classes of chromophores, to facilitate label choice and to address future challenges in the rational design and manipulation of QD labels.

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Quantum dots versus organic dyes as fluorescent labels

Chemically derived graphene oxide (GO) is an atomically thin sheet of graphite that has traditionally served as a precursor for graphene, but is increasingly attracting chemists for its own characteristics. It is covalently decorated with oxygen-containing functional groups - either on the basal plane or at the edges - so that it contains a mixture of sp(2)- and sp(3)-hybridized carbon atoms. In particular, manipulation of the size, shape and relative fraction of the sp(2)-hybridized domains of GO by reduction chemistry provides opportunities for tailoring its optoelectronic properties. For example, as-synthesized GO is insulating but controlled deoxidation leads to an electrically and optically active material that is transparent and conducting. Furthermore, in contrast to pure graphene, GO is fluorescent over a broad range of wavelengths, owing to its heterogeneous electronic structure. In this Review, we highlight the recent advances in optical properties of chemically derived GO, as well as new physical and biological applications.

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Graphene oxide as a chemically tunable platform for optical applications

We report that nanoscale carbon particles (carbon dots) upon simple surface passivation are strongly photoluminescent in both solution and the solid state. The luminescence emission of the carbon dots is stable against photobleaching, and there is no blinking effect. These strongly emissive carbon dots may find applications similar to or beyond those of their widely pursued silicon counterparts.

http://www.ecs.umass.edu/ece697mm/Supplement_Clemson_Cbased_Qdots_JAmChemSoc_05_06.pdf

Quantum-sized carbon dots for bright and colorful photoluminescence.

Carbon nanoparticles upon simple surface passivation exhibit bright photoluminescence. Reported here is a new finding that these carbon dots are also strongly two-photon luminescent with pulsed laser excitation in the near-infrared. The experimentally measured two-photon absorption cross-sections are comparable to those of the high-performance semiconductor quantum dots already available in the literature. The two-photon luminescence microscopy imaging of human breast cancer cells with internalized carbon dots is demonstrated.

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Carbon dots for multiphoton bioimaging

Photoinduced electron transfers with carbon dots

Single‐Walled Carbon Nanotubes Tethered with Porphyrins: Synthesis and Photophysical Properties

Using sonochemistry to provide the thermal energy and mixing, we demonstrate the ability to synthesize air-stable aluminum nanoparticles of two different size distributions from the titanium-catalyzed thermal decomposition of alane. Characterization data indicate the presence of spherical face-centered-cubic aluminum nanoparticles with average sizes of either 5 or 30 nm that are capped with an organic shell. The average size of the nanoparticles correlates with the concentration of the passivation agent oleic acid, where a higher concentration results in smaller particles. Thermal analysis data demonstrates that at elevated temperatures (>550 °C), these particles react via a typical aluminum oxidation mechanism, whereas at low temperatures (<550 °C), the behavior of these particles is unique and directly related to the presence of the organic shell.

Sonochemically Assisted Thermal Decomposition of Alane N,N-Dimethylethylamine with Titanium (IV) Isopropoxide in the Presence of Oleic Acid to Yield Air-Stable and Size-Selective Aluminum Core−Shell Nanoparticles

Barbara A. Harruff

Papers

Quantum-sized carbon dots for bright and colorful photoluminescence.

Carbon dots for multiphoton bioimaging

Photoinduced electron transfers with carbon dots

Single‐Walled Carbon Nanotubes Tethered with Porphyrins: Synthesis and Photophysical Properties

Sonochemically Assisted Thermal Decomposition of Alane N,N-Dimethylethylamine with Titanium (IV) Isopropoxide in the Presence of Oleic Acid to Yield Air-Stable and Size-Selective Aluminum Core−Shell Nanoparticles