Renal-Clearable Biomass-Derived Carbon Dots with Red Fluorescence for Masked Cryptic Kidney Injury Imaging

Masked cryptic kidney injury (MCKI), an early stage of acute kidney injury (AKI), is challenging to detect and diagnose, especially in the modern context where toxic substances, such as surfactants, are increasingly misused. Consequently, there is an urgent need for methods for the visual diagnosis of MCKI. In this study, we synthesized environmentally friendly spirulina-derived carbon dots (SpiCDs) using spirulina as a biobased raw material through a simple hydrothermal process. These SpiCDs, with their ultrasmall size, enable efficient renal clearance. In cellular experiments, SpiCDs rapidly entered SDS-damaged cells, facilitating dynamic monitoring of the cell membrane damage process. In vivo animal experiments demonstrated that SpiCDs were efficiently excreted through the kidneys and began to accumulate in the bladder within 10 min after tail vein injection. The detection of red fluorescence in excreted urine confirmed the renal metabolic pathway of the SpiCDs. Furthermore, in an MCKI model induced by SDS, SpiCDs showed accelerated excretion and earlier accumulation in the bladder, indicating an increased sensitivity to kidney injury. These results suggest that SpiCDs provide a promising approach for the early diagnosis of MCKI, offering insights into its visual detection and monitoring.