Simultaneous Electrochemical and Fluorescent In Situ Analysis of PD-1 on Tumor Cells via ZIF-8-Enhanced Quantum Dot Signal Amplification

Although immunotherapy has become an established approach in cancer treatment, not all patients exhibit a positive response. Current research on PD-1 primarily focuses on immune cells using conventional methods, yet PD-1 expression on tumor cells is also widespread and plays an increasingly critical role in assessing immunotherapy efficacy. To address this, we developed an electrochemical biosensor capable of specifically detecting PD-1 at both the protein and tumor cellular levels in situ, eliminating the need for sample fixation and thereby streamlining the analytical process. Additionally, our probe enables simultaneous localization analysis of PD-1 through fluorescence signaling. The biosensor integrates a bifunctional probe composed of a nanometal–organic framework (MOF, ZIF-8) conjugated with quantum dots (QDs) and an electrode modified with a carbon nanotube (CNT)–gold nanoparticle (AuNP) nanocomposite. The morphology and performance of the nanocomposite were thoroughly characterized, and the resulting PD-1 biosensor demonstrates high specificity, reproducibility, and sensitivity. To facilitate clinical translation, we successfully applied the biosensor to detect differential PD-1 expression across various tumor cell lines and cancer tissues. This study establishes that our dual-mode electrochemical and fluorescent sensing platform provides a powerful tool for in situ PD-1 detection on tumor cells, offering valuable insights for evaluating tumor immunotherapy responses.