Applied Nano

Fluorescent nitrogen-doped carbon dots (TRCDs) were synthesized from tomato residues (TR) by hydrothermal carbonization, and the effects of parameters like temperature, reaction time, nitrogen precursor, and ethylenediamine/tomato residue (EDA/TR) mass ratio on their photophysical and biological properties were investigated. The optimal synthesis conditions were achieved at 250 °C for 6 h using an EDA/TR mass ratio of 0.08, yielding an aqueous carbon dot fraction in 17.6% (w/w). TRCDs exhibit a strong blue fluorescence, with a fluorescence quantum yield of 0.17, at an emission wavelength of 460 nm. AFM and TEM analyses showed well-dispersed quasi-spherical nanoparticles with dimensions characteristic of carbon dots. The synthesized TRCDs, produced with different additives, demonstrate antioxidant activity in both ABTS^•+ and DPPH^• assays, reaching values of up to 969 and 75 µg Trolox equivalents (TE)/mg TRCDs, respectively. Cytotoxicity studies indicate cell viability in above 80% up to 500 μg/mL in all tested cell lines and above 90% in VERO cells at concentrations up to 2000 μg/mL, while fluorescence microscopy revealed cell-associated fluorescence following TRCD exposure, supporting their potential application as fluorescent cellular markers.

The structural properties and dynamics of water molecules dispersed among gold nanoclusters (GNCs) of different sizes were studied using molecular dynamics (MD) simulations. Spherical GNCs of five different diameters were placed in a cubic simulation box with a fixed edge length, while the remaining volume was filled with water molecules sufficient to reproduce the experimental density of these Au/water systems at a temperature of 300 K. MD simulations show that the size of Au nanoclusters has a significant effect on the dynamics of water molecules in Au/water systems. By calculating the slope of the mean square displacement of the centers of mass of water molecules in the Au/water systems and using the Einstein relation, the average diffusion coefficients D of these molecules were obtained. It was found that the values of D decrease as the size of the Au nanoclusters increases, while the values of the shear viscosity of water increase significantly as the size of the Au nanoclusters increases up to 1.5 nm in diameter. In turn, the size of the GNCs has a weak effect on the position of the first peak in the radial distribution functions $G\left(r\right)$, corresponding to the first coordination shell of nearest neighbors. As the distance r increases, the height of the second and third peaks decreases and disappears, which probably indicates that the H₂O molecules are moving away from the hydroxyl groups.

Marine protein hydrolysates are valuable sources of antioxidant bioactive peptides but are susceptible to degradation during processing and storage. Encapsulation can improve their stability and facilitate their incorporation into food matrices. This study evaluated the encapsulation and antioxidant activity retention of a sardine protein hydrolysate (SPH) from Opisthonema bulleri, O. libertate, and O. medirastre. The SPH contained 61.88 ± 0.84 g kg⁻¹ crude protein, with 71.58 ± 1.54% of peptides ranging from 1.35 to 17 kDa. SPH was encapsulated by spray drying using maltodextrin and gum arabic under three processing conditions. FTIR revealed spectral changes after encapsulation, while AFM showed differences in nanoscale surface features. Processing conditions significantly affected production yield, surface feature size, and antioxidant activity retention. ESPH1 (150 °C inlet temperature, 60 °C outlet temperature, and 9.4 mL min⁻¹ feed flow rate) showed the highest production yield (69.13 ± 0.72%), smallest surface features (141 ± 32 nm), and antioxidant activity retention of 67.41% for ABTS, 70.76% for DPPH, and 99.85% for FRAP. These findings support spray-dried SPH as a potential powdered antioxidant functional ingredient for incorporation into food formulations.