RESEARCH PAPER Nitrogen-doped carbon dots embedded in a SiO 2 monolith for solid-state fluorescent detection of Cu 2+ ions Luisa Sciortino & Fabrizio Messina & Gianpiero Buscarino & Simonpietro Agnello & Marco Cannas & Franco M. Gelardi Received: 7 March 2017 /Accepted: 2 June 2017 # Springer Science+Business Media B.V. 2017 Abstract We describe the simple fabrication of SiO 2 sol-gel monoliths embedding highly luminescent carbon nanodots (CDs) sensitive to metal ions. The pristine CDs we synthesize display an intense dual emission consisting in two fluorescence bands in the green and violet region, and we demonstrate that this photoluminescence is substantially unchanged when the dots are incorporated in the SiO 2 matrix. The emission of these CDs is quenched by interac- tions with Cu 2+ ions, which can be used to detect these ions with a detection limit of 1 μM. The chromophores remain accessible to diffusing Cu 2+ ions even after embedding CDs in the sol-gel mono- lith, where their detection capabilities are preserved. Such a result provides the proof-of-principle of a new sensing scheme, where CDs are exploited as active sensing centers of metal transition ions within a solid-state device. The different interaction mech- anisms of CDs with copper, in liquid and solid phase, are analyzed in detail and discussed in terms of different accessibility of their chromophores when the dots are incorporated in the SiO 2 matrix. Keywords Carbondots . Ratiometricsensor . Functional materials . Photoluminescence . Sensor Introduction Carbon dots (CDs) currently motivate a strong interest because of their bright and tunable fluorescence, typi- fied by a broad emission with marked excitation- wavelength dependence and large quantum yield (Yang et al. 2009a, b; Wang et al. 2010). Although the structure of CDs is rather synthesis-dependent, the abun- dance of certain organic moieties at their surface such as carboxyl (Vinci and Colón 2013), carbonyl (Vinci and Colón 2013; Bao et al. 2011), amine, and amide (Bourlinos et al. 2008) is well-established, and the co- existence of carbon atoms with different hybridizations (sp 3 and sp 2 ) was proved by Raman experiments (Hsu and Chang 2012). CDs are generally classified in carbon quantum dots (CQDs), characterized by well-defined crystalline structures and quantum confinement effects, and carbon nanodots (CNDs) characterized by fluores- cence from surface-localized states and amorphous structures (Cayuela et al. 2016). Nevertheless, this view of the CD families might be incomplete, as we recently identified another class of carbon-based dots, β-C 3 N 4 , combining the crystalline structure of CQDs with the emissive surface states typical of CNDs (Messina et al. 2016a, b). Anyway, the source of the peculiar optical properties of CDs is still largely debated, but surely, the small size of the dots (typically <10 nm), the nature of surface groups, and doping with heteroatoms all play a J Nanopart Res (2017) 19:228 DOI 10.1007/s11051-017-3915-6 Electronic supplementary material The online version of this article (doi:10.1007/s11051-017-3915-6) contains supplementary material, which is available to authorized users. L. Sciortino : F. Messina (*) : G. Buscarino : S. Agnello : M. Cannas : F. M. Gelardi Dipartimento di Fisica e Chimica, Università degli Studi di Palermo, Via Archirafi, 36, 90123 Palermo, Italy e-mail: fabrizio.messina@unipa.it