This journal is © The Royal Society of Chemistry 2025 J. Mater. Chem. B, 2025, 13, 2029–2041 | 2029Cite this: J. Mater. Chem. B, 2025,13, 2029Nitrogen doped carbon dots for in vitrointracellular redox modulation via opticalstimulation†P. Lagonegro,‡* ab C. Marzuoli, ‡ bc G. Tullii,bF. Rossi,dC. Bellacanzone,bE. Mancinelli,bF. Turco, a B. M. Squeo,aM. Pasini * a andM. R. AntognazzabCarbon dots (CDs) are promising candidates as oxygen photosensitizers, in cancer therapeuticapplications due to their high quantum yield, superior chemical and photostability, low cytotoxicity and easeof chemical functionalization/tuning. Nitrogen doping can further improve oxygen photosensitizationperformance. Besides photodynamic therapy, however, the possibility to finely and remotely regulate theintracellular redox balance by using physical stimuli has been attracting more and more interest not only fornanotheranostic application, but also as a novel, fully biocompatible therapeutic tool. Here, we report on thesynthesis of nitrogen-doped CDs by solvothermal methods starting from abundant, bioderived, low-costprecursors, and we characterize their interface with in vitro cultures of human embryonic kidney (HEK-293)cells, a widely accepted model of non-tumoral cells. While not af f ecting cell proliferation, synthesized CDsef f i ciently modulate, under visible light and physiological eustress conditions, intracellular calcium iondynamics and reactive oxygen species concentration, resulting in a 4-fold increase. The reported resultsmay broaden the application of CDs beyond photodynamic therapy, unveiling new opportunities in the fieldof redox medicine assisted by carbon-based nanomaterials and optical stimulation.IntroductionCarbon dots (CDs) represent one of the most recent additions tothe carbon-based nanomaterial family. Discovered in the early2000s, 1 these nanoparticles exhibit a spherical morphology withdiameters below 10 nm. 2 They can be synthesized using both top-down approaches, such as the exfoliation of graphite, and bottom-up methods from carbon-rich precursors, 3 including plasticwaste 4 or agro-industrial residues. 5 The carbon within these dotscan exist in various hybridization states, ranging from fullyamorphous 6 to having a graphitic core, 7,8 depending on thesynthesis conditions. 9 This structural and compositional versati-lity endows carbon dots with a wide array of properties, makingthem a key subject of study in current nanotechnology research. 10Among other applications, CDs have been largely employed forphotocatalysis, 11 as sensitizers for solar cells 12 as well as for lightemission and sensing, 1,13–15 taking full advantage of distinctivelightabsorptionand charge generationcapability.Nitrogen-dopedcarbon dots have also been reported, in combination with silvernanoparticles, as effective electrocatalysts for the oxygenreduction reaction, with high catalytic activity and superior stabi-lity compared to commercial Pt/C catalysts. 16 The peculiar proper-ties of CDs have been exploited not only in the photonics andoptoelectronic fields, but also in biotechnology. 17–19 Their excel-lent biocompatibility and water solubility are key features for theirbiological applications, in particular for in vitro cell labelling 20,21and in vivo tissue imaging. 22 Bright photoluminescence in thevisible spectrum, high photostability, broad excitation spectrumand tunable emission spectra promoted the use of CDs as avaluable alternative to conventional organic dyes and semicon-ductor quantum dots. 23 Thus, they have been explored as efficientlight emitters for a range of techniques, including fluorescenceimaging, magnetic resonance imaging, and photoacoustic ima-ging. Moreover, CDs have been explored as catalyst carriers indrug delivery systems, as well as active agents in photothermaland photodynamic tumor therapies. 24Nitrogen doping 25–30 is widely reported as an effective andsustainable method for modulating the optical properties ofCDs (N-CDs). 31 By incorporating nitrogen in various forms sucha Istituto di Scienze e Tecnologie Chimiche ‘‘Giulio Natta’’ (SCITEC)-CNR,20133 Milano, Italy. E-mail: mariacecilia.pasini@cnr.scitec.itb Center for Nano Science and Technology, Istituto Italiano di Tecnologia,20134 Milano, Italy. E-mail: paola.lagonegro@iit.itc Dipartimento di Fisica, Politecnico di Milano, 20133 Milano, Italyd IMEM-CNR Institute, Parco Area delle Scienze 37/A, 43124, Parma, Italy† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4tb01698j‡ P. Lagonegro and C. Marzuoli equally contributed to this work.Received 31st July 2024,Accepted 23rd December 2024DOI: 10.1039/d4tb01698jrsc.li/materials-bJournal ofMaterials Chemistry BPAPEROpen Access Article. Published on 13 January 2025. Downloaded on 6/21/2026 2:58:34 AM. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article OnlineView Journal | View Issue
