Preparation of hydrophobic carbon dots for lipid content detection in Schizochytrium

Schizochytrium an oleaginous microorganism widely used in industrial production of polyunsaturated fatty acids, requires precise quantification of lipid content as a key indicator for strain screening. To address the labor-intensive and expensive nature of conventional methods, this study developed a rapid fluorescence detection strategy using carbon dots (CDs). We synthesized nitrogen and sulfur co-doped CDs (NS-CDs) through a one-step solvothermal method with o-phenylenediamine and dithiosalicylic acid as precursors in N, N-dimethylformamide (DMF). The NS-CDs exhibited good hydrophobicity, robust photostability, low cytotoxicity, and a high quantum yield (QY) of 52%. With dimethyl sulfoxide (DMSO) facilitating cellular uptake, the NS-CDs achieved efficient fluorescence imaging of Schizochytrium. Under optimized conditions (25% (v/v) DMSO, NS-CDs concentration of 40 mg/mL, 40 °C with 6-min dark incubation), fluorescence intensity of labeled Schizochytrium suspensions showed a significant linear correlation with lipid content (R2 = 0.9964), with a LOD of 0.0336 g/L, RSD of 1.4%–3.4%, and relative errors of 0.5%–1.5%. Thus, this NS-CDs-based fluorescence strategy establishes a rapid platform for lipid quantification in Schizochytrium, enabling efficient industrial screening of high-lipid strains.