Blue light-emitting carbon dots (CDs) from a milk protein and their interaction with Spinacia oleracea leaf cells

The milk protein casein (Cas) has been employed as carbon resource material to synthesize nitrogen-doped carbon dots (N-CDs) via microwave exposure. The dots, when exposed to UV light, produced blue fluorescence. The N-CDs were characterized by ultra violet (UV) spectroscopy, Fourier transformation infrared spectroscopy, X-ray diffraction (XRD), dynamic light scattering analysis, fluorescent microscopy (FM), and transmission electron microscopy (TEM). The XRD analysis revealed a broad peak at 2θ = 20°, thus indicating the turbostratic carbon phase. TEM analysis and particle size distribution curve revealed that nearly, 85% of the particles had diameter below 10 nm and the particles had spherical geometry. The HRTEM analysis revealed that carbon dots exhibited lattice fringes with a d-spacing of 0.21 nm, corresponding to the (100) plane lattice of graphite. The fluorescence spectral studies indicated a red shift in the emission peak from 420 to 450 nm as the excitation wavelength increased from 300 to 340 nm. The zeta potential of particles was found to be –11.3 mV. Finally, impregnation of N-CDs was studied in Spinacia oleracea leaf. It was observed that as the concentration of N-CDs’ solution increased, percent insertion (PI) also increased, but the time required for maximal insertion decreased with increasing concentrations of N-CDs in the feed solutions. In the carbon dots’ solution with a concentration of 200 ppm, maximum percent insertion (MPI) was obtained after 80 min. However, with the increasing concentration of N-CDs in the feed solutions, time of getting MPI reduced, i.e., in 600 ppm, it was 30 min, and in 800 ppm, it was 10 min.