Eco-Friendly Synthesis of L-Carnitine-Loaded β-Cyclodextrin-Functionalized N-Doped Carbon Dots Using Rhododendron Species: Antioxidant and Antimicrobial Activities and In Vivo Acute Toxic Effects on Nauplii

In this study, N-doped carbon dots (CDs) functionalized with L-carnitine-loaded β-cyclodextrin were synthesized with a hydrothermal method using two different Rhododendron spp. (R. luteum and R. ponticum) as carbon sources. The synthesized carbon dots (LC/β-CD@Rh.l/N-CD (CD1) and LC/β-CD@Rh.p/N-CD (CD2)) showed monodisperse distributions, with a size of 3–5 nm and a spherical structure. The stability of these biogenic CDs in water and their effects on marine ecosystems were investigated using A. salina larvae (nauplii). Biogenic CDs were exposed to varying concentrations of 5–100 μL for 24, 48, 72, and 96 h, and the LC50 values were calculated as 12.858 µg/L for CD1 and 21.058 µg/L for CD2. Bactericidal and fungicidal activities of CDs at sublethal concentrations were observed to have similar effects. Likewise, antioxidant activities (SOD, CAT), oxidative stress markers (ROS, MDA), and DPPH radical scavenging activities were investigated; SOD, CAT, and MDA activities varied depending on the exposure time of the larvae. Additionally, CDs induced high ROS generation and DPPH radical scavenging activity in nauplii. In fluorescence microscopy and TEM micrographs, different structural abnormalities were detected in larvae depending on the concentration of CDs, such as various degrees of abdominal fractures and fragmentation, and limb loss.