Bioimaging supported by nanoparticles requires low cost, highly emissive and photostable systems with low cytotoxicity. Carbon dots (C-dots) offer a possible solution, even if controlling their properties is not always straightforward, not to mention their potentially simple synthesis and the fact that they do not exhibit long-term photostability in general. In the present work, we synthesized two C-dots starting from citric acid and tris (hydroxymethyl)-aminomethane (tris) or arginine methyl ester dihydrochloride. Cellular uptake and bioimaging were tested in vitro using murine neuroblastoma and ovine fibroblast cells. The C-dots are highly biocompatible, and after 24 h of incubation with the cells, 100% viability was still observed. Furthermore, the C-dots synthesized using tris have an average dimension of 2 nm, a quantum yield of 37%, high photostability and a zeta potential (ζ) around −12 mV. These properties favor cellular uptake without damaging cells and allow for very effective bioimaging.

The class of diamino-naphthalene exhibits antioxidant properties, which are partly related to the relative positions of the two amino groups. This study demonstrates how the reactivity of one of these compounds, 1,5-diamino-naphthalene (DAN), can be adjusted by introducing a single amide bond through a simple thermal coupling with l-pyroglutamic acid (PyroGlu). The solventless thermal reaction between PyroGlu and DAN at 160 °C yielded a new mono-pyroglutanilide compound (PyroDAN) that was characterized using various analytical techniques, including a thermal and infrared analysis, HRMS (ESI), and one- (1D) and two-dimensional (2D) NMR. The optical properties were investigated using UV-Vis and fluorescence spectroscopy. Additionally, two chemical standard assays were used to measure both the antioxidant and pro-oxidant properties of PyroDAN. The molecule has shown nearly negligible pro-oxidant activity, while a mild antioxidant activity is still retained. These findings indicate that the transformation of DAN into a mono-pyroglutanilide derivative breaks the original molecular symmetry and effectively modifies the electronic distribution of the aromatic system, suppressing the oxidant properties while keeping a mild antioxidant activity. Furthermore, the tuneable fluorescent properties of PyroDAN—the mild antioxidant activity and the inhibition of the cytologically harmful pro-oxidant properties—suggest promising applications in bioimaging and other biological fields.

Cell spheroids are widely studied for their potential applications in tissue engineering and regenerative medicine. The present work investigated the effects of cryopreservation on spheroids derived from ovine fibroblasts, depending on spheroid size (140 or 220 µm). Specifically, it explored how cryopreservation impacted several biological and physical parameters including cell damage, viability, metabolism, adhesion, proliferation, and spheroid mass density, weight, and diameter at three time points after thawing. A Live/Dead assay provided a visual assessment of cell damage, cell viability and metabolic activity were assessed by an Alamar Blue assay, and a replating assay evaluated cell adhesion and proliferation capabilities. Spheroid mass density, weight, and diameter were quantified by the W8 Biophysical Analyzer, creating accurate biophysical profiles. Real-time PCR (RT-PCR) analysis was employed to uncover gene expression changes following cryopreservation. Our findings indicate that spheroids measuring 140 µm in diameter largely maintained their biophysical features and cell viability post-cryopreservation, whereas those at 220 µm exhibited a decline in both vitality and mass density. The reduced vitality of 220 µm spheroids likely reflects size-related limitations in cryoprotectant diffusion and stress within the core. Overall, this study provides a comprehensive understanding of how cryopreservation affects ovine fibroblast spheroid biophysics and cellular integrity, laying the groundwork for improved preservation techniques for cell spheroids.