Label-free fluorescent sensor for sensitive detection of ctDNA based on water stabilized CsPbBr₃ nanosheet

The detection of circulating tumor DNA (ctDNA), as a practical liquid biopsy technique, was of great significance for the study of cancer diagnosis and prognosis. However, reported methods for detection ctDNA still have some limitations, such as tedious process and high cost. In this study, CsPbBr₃ nanosheet (CsPbBr₃ NS) with high water stability was prepared by etching, and its fluorescence intensity could be stably stored for 1 year. The Ti₃C₂T_x possessed high quenching efficiency for CsPbBr₃ NS and the HOMO-LUMO orbital study revealed that the PET mechanism was responsible for fluorescence quenching. And the Ti₃C₂T_x showed stronger affinity towards single-stranded DNA (ssDNA), as compared with double-stranded DNA (dsDNA). The probe ssDNA could be adsorbed on the surface of Ti₃C₂T_x through π-π stacking. After the targets were recognized by probe ssDNA to form dsDNA, its affinity with Ti₃C₂T_x decreased and the active site of Ti₃C₂T_x recovered, causing a high quenching efficiency on CsPbBr₃ NS. Based on this, a label-free fluorescent biosensor was designed for the sensitive detection of ctDNA (EGFR 19 Dels for non-small cell lung cancer, NSCLC). Under the optimal experimental conditions, this biosensor exhibited a detection limit of 180 fM and a linear range of 50 pM-350 pM with amplification of magnetic beads through strand displacement reaction. In addition, this sensor was applied to the detection of ctDNA in serum samples and cells lysates. This method for ctDNA detection was expected to have great potential for biomarker detection in the field of liquid biopsy.