Carbon dots: synthesis, formation mechanism, fluorescence origin and sensing applications

In the most recent decade, carbon dots have drawn intensive attention and triggered substantial investigation. Carbon dots manifest superior merits, including excellent biocompatibility both in vitro and in vivo, resistance to photobleaching, easy surface functionalization and bio-conjugation, outstanding colloidal stability, eco-friendly synthesis, and low cost. All of these endow them with the great potential to replace conventional unsatisfactory fluorescent heavy metal-containing semiconductor quantum dots or organic dyes. Even though the understanding of their photoluminescence mechanism is still controversial, carbon dots have already exhibited many versatile applications. In this article, we summarize and review the recent progress achieved in the field of carbon dots, and provide a comprehensive summary and discussion on their synthesis methods and emission mechanisms. We also present the applications of carbon dots in bioimaging, drug delivery, microfluidics, light emitting diode (LED), sensing, logic gates, and chiral photonics, etc. Some unaddressed issues, challenges, and future prospects of carbon dots are also discussed. We envision that carbon dots will eventually have great commercial utilization and will become a strong competitor to some currently used fluorescent materials. It is our hope that this review will provide insights into both the fundamental research and practical applications of carbon dots.

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Novel properties and applications of carbon nanodots

Conducting hydrogels provide great potential for creating designer shape-morphing architectures for biomedical applications owing to their unique solid-liquid interface and ease of processability. Here, a novel nanofibrous hydrogel with significant enzyme-like activity that can be used as "ink" to print flexible electrochemical devices is developed. The nanofibrous hydrogel is self-assembled from guanosine (G) and KB(OH)4 with simultaneous incorporation of hemin into the G-quartet scaffold, giving rise to significant enzyme-like activity. The rapid switching between the sol and gel states responsive to shear stress enables free-form fabrication of different patterns. Furthermore, the replication of the G-quartet wires into a conductive matrix by in situ catalytic deposition of polyaniline on nanofibers is demonstrated, which can be directly printed into a flexible electrochemical electrode. By loading glucose oxidase into this novel hydrogel, a flexible glucose biosensor is developed. This study sheds new light on developing artificial enzymes with new functionalities and on fabrication of flexible bioelectronics.

Self-Assembly of Enzyme-Like Nanofibrous G-Molecular Hydrogel for Printed Flexible Electrochemical Sensors.

The incorporation of biomolecules into nanomaterials generates functional nanosystems with novel and advanced properties, presenting great potential for applications in various fields. Nucleobases, nucleosides and nucleotides, as building blocks of nucleic acids and biological coenzymes, constitute necessary components of the foundation of life. In recent years, as versatile biomolecules for the construction or regulation of functional nanomaterials, they have stimulated interest in researchers, due to their unique properties such as structural diversity, multiplex binding sites, self-assembly ability, stability, biocompatibility, and chirality. In this review, strategies for the synthesis of nanomaterials and the regulation of their morphologies and functions using nucleobases, nucleosides, and nucleotides as building blocks, templates or modulators are summarized alongside selected applications. The diverse applications range from sensing, bioimaging, and drug delivery to mimicking light-harvesting antenna, the construction of logic gates, and beyond. Furthermore, some perspectives and challenges in this emerging field are proposed. This review is directed toward the broader scientific community interested in biomolecule-based functional nanomaterials.

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Nucleobases, nucleosides, and nucleotides: versatile biomolecules for generating functional nanomaterials

Light-emitting chiral carbonized polymer dots (Ch-CPDs) are attracting great interest because of their extraordinary photonic properties, but modulating their band-gap emission, especially at long wavelength, and maintaining their chiral structure to achieve multicolor, high-emission Ch-CPDs remains challenging. Reported here for the first time is the synthesis of red- and multicolor-emitting Ch-CPDs using the common precursors L-/D-tryptophan and o-phenylenediamine, and a solvothermal approach at one temperature. The quantum yield of the Ch-CPDs was between 31 % and 54 %. Supramolecular self-assembly provided multicolor-emitting Ch-CPDs showing novel circularly polarized luminescence, with the highest dissymmetric factor (glum ) of 1×10-2 . Importantly, circularly polarized white-emitting CPDs were fabricated for the first time by tuning the mixing ratio of the three colored Ch-CPDs in a gel. This strategy affords exciting opportunities for designing functional chiroptical materials.

Rational Design of Multicolor-Emitting Chiral Carbonized Polymer Dots for Full-Color and White Circularly Polarized Luminescence

Hydrogels are attractive materials for designing sensors, catalysts, scaffolds for tissue engineering, stimuli responsive soft materials, and controlled-release drug delivery systems. In recent years, self-assembly of guanosine and its derivatives has received immense interests for devising programmable supramolecular biomaterials including hydrogels. This perspective highlights some of the history and the recent developments of guanosine-based supramolecular hydrogels and their applications. Future prospects and scope of the guanosine-based hydrogels have also been discussed.

Guanosine-Derived Supramolecular Hydrogels: Recent Developments and Future Opportunities.

Chiral carbon dots derived from guanosine 5'-monophosphate form supramolecular hydrogels.

We herein report that hydrogels can be prepared from guanosine and boronic acids in the presence of K+ and Pb2+ ions. These supramolecular hydrogels are formed via G-quartet like self-assembly of guanosine and its boronate esters. The potential of this hydrogel construct in mimicking enzyme-like activity has been demonstrated for the first time. We have observed that the self-assembled structure present in K+ stabilized hydrogel binds to iron(III)-hemin and shows peroxidase activity, catalyzing oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2. Furthermore, the conformation of the G-quartet assemblies in the hydrogel can be altered by varying the stabilizing cations K+ and Pb2+. This conformational switching has been used to devise a molecular logic gate for sensing of toxic Pb2+ ions.

Supramolecular Hydrogel Inspired from DNA Structures Mimics Peroxidase Activity

We herein report the preparation of hydrogels by the Ag+ ion induced assembly of cytidine and boronic acids. These hydrogels, presumably formed by an i-motif like arrangement of cytidine and its bo...

Tanima Bhattacharyya

Papers

Guanosine-Derived Supramolecular Hydrogels: Recent Developments and Future Opportunities.

Chiral carbon dots derived from guanosine 5'-monophosphate form supramolecular hydrogels.

Supramolecular Hydrogel Inspired from DNA Structures Mimics Peroxidase Activity

Cytidine-Derived Hydrogels with Tunable Antibacterial Activities

Supramolecular Template-Directed In Situ Click Chemistry: A Bioinspired Approach to Synthesize G-Quadruplex DNA Ligands.