Fluorescent nanodots have become increasingly prevalent in a wide variety of applications with special interest in analytical and biomedical fields. The present overview focuses on three main aspects: (i) a systematic description and reasonable classification of the most relevant types of fluorescent nanodots according to their nature, quantum confinement and crystalline structure is provided, starting with a clear distinction between semiconductor and carbon-based dots (graphene quantum dots, carbon quantum dots and carbon nanodots). A new set of abbreviations and definitions for them to avoid contradictions found in literature is also proposed; (ii) a rational classification allows the establishment of clear-cut differences and similarities among them. From a basic point of view, the origins of the photoluminescence of the different nanodots are also established, which is a relevant contribution of this overview. Additionally, the most outstanding similarities and differences in a great variety of criteria (i.e. year of discovery, synthesis, the physico-chemical characteristics like structure, nature, shape, size, quantum confinement, toxicity and solubility, the optical characteristics including the quantum yield and lifetime, limitations, applications as well as the evolution of publications) are thoroughly outlined; and (iii) finally, the promising future of fluorescent nanodots in both analytical and biomedical fields is discussed using selected examples of relevant applications.

We report the incorporation of functionalised carbon nanodots within a low molecular weight salt hydrogel enhancing the gelation and fluorescence properties of both the gel and carbon nanomaterial.

Citation for published item:gyuelD engelin nd orinoD wF vur nd uennedyD turt F nd teedD tF F nd l¡ relD wF @PHITA 9pluoresent ron quntum dot hydrogels for diret determintion of silver ionsF9D lntFD ISI F ppF IHHEIHSF Further information on publisher's website: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACTThe paper reports for the first time the direct determination of silver ion (Ag + ) using luminescent Carbon Quantum Dot hydrogels (CQDGs). Carbon Quantum Dots (CQDs) with different superficial moieties (passivate-CQDs with carboxylic groups, thiol-CQDs and amine-CQDs) were used to prepare hybrid gels using a low molecular weight hydrogelator (LMWG). The use of the gels results in considerable fluorescence enhancement and also markedly influences selectivity. The most selective CQDG system for Ag + ion detection proved to be those containing carboxylic groups onto their surface. The selectivity towards Ag + ions is possibly due to its flexible coordination sphere compared with other metal ions.This fluorescent sensing platform is based on the strong Ag-O interaction which can quench the photoluminescence of passivate-CQDs (p-CQDs) through charge transfer. The limit of detection (LOD) and quantification (LOQ) of the proposed method were 0.55 and 1.83 µg·mL -1 , respectively, being applied in river water samples.

A selective photoluminescence method based on Carbon Quantum Dots (CQDs) functionalized with carboxymethyl-β-cyclodextrin for the direct determination of water-soluble C60 fullerene has been developed. CQDs were synthesized using a top-down methodology from multiwall carbon nanotubes (MWCNTs) and further functionalized with N-Boc-ethylenediamine to confer monoprotected amine groups onto their surface. Once amine-functionalized CQDs were obtained after deprotection, an amidation reaction with carboxymethyl-β-cyclodextrin cavitands was achieved and the obtained fluorescent β-cyclodextrin functionalized Carbon Quantum Dots (cd-CQDs) were investigated for the inclusion complexation of water-soluble C60. Quenching of their fluorescence was observed owing to the non-covalent self-assembly of cd-CQDs and C60, making possible the quantification of C60. A method to determine water-soluble C60 is then proposed with detection and quantification limits of 0.525 and 1.751 μg mL(-1), respectively. The method was validated by determining soluble C60 fullerene in spiked river water. One added value of the paper is the fact that it can be ascribed to the "Third Way in Analytical Nanoscience and Nanotechnology".

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The photoluminescence behaviour of carbon-based nanodots is still debated. Both core and surface structures are involved in the emission mechanism, and the electronic transitions can be modified by external agents such as metal ions or pH, but the general relation between the structure and the optical function is poorly understood. Here, we report a comparative study on the effects of these variables, changing the core structure from crystalline to amorphous, and modifying the surface structure by different passivation procedures. Our results highlight that the emission mechanism of the tunable visible fluorescence is identical for crystalline and amorphous samples, indicating the independence of the emission from the core structure. Furthermore, surface functionalization weakly influences the emission peak position, but has large consequences on their interaction with different metal ions. This suggests the involvement of quasi-degenerate electronic states originating from the high density of different interacting groups on the surface. Finally, we report the presence of an unusual ultraviolet emission band for the amorphous sample, likely involving localized molecular-type chromophores with carboxyl ends. Our findings provide new information on the emission mechanisms of CDs and can be used to engineer sub-types of CDs displaying very similar emission features, but specifically tailored for different sensing applications.

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