Peptide-Based Photoelectrochemical Cytosensor Using a Hollow-TiO₂/EG/ZnIn₂S₄ Cosensitized Structure for Ultrasensitive Detection of Early Apoptotic Cells and Drug Evaluation

The ability to rapidly detect apoptotic cells and accurately evaluate therapeutic effects is significant in cancer research. To address this target, a biocompatible, ultrasensitive photoelectrochemical (PEC) cytosensing platform was developed based on electrochemically reduced graphene (EG)/ZnIn₂S₄ cosensitized TiO₂ coupled with specific recognition between apoptotic cells and phosphatidylserine-binding peptide (PSBP). In this strategy, the HL-60 cells were selected as a model and C005, nilotinib, and imatinib were selected as apoptosis inducers to show cytosensing performances. In particular, a TiO₂ photoactive substrate was designed as hollow spheres to enhance the PEC performance. Graphene was electrodeposited on the hollow TiO₂-modified electrode to accelerate electron transfer and increase conductivity, followed by in situ growth of ZnIn₂S₄ nanocrystals as photosensitizers via successive ionic layer adsorption and reaction method, forming a TiO₂/EG/ZnIn₂S₄ cosensitized structure that was used as a PEC matrix to immobilize PSBP for the recognition of early apoptotic cells. The detection of apoptotic cells was based on steric hindrance originating from apoptotic cell capture to induce an obvious decrease in the photocurrent signal. The ultrahigh sensitivity of the cytosensor resulted from enhanced PEC performance, bioactivity, and high binding affinity between PSBP and apoptotic cells. Compared with other assays, incorporate toxic elements were avoided, such as Cd, Ru, and Te, which ensured normal cell growth and are appropriate for cell analysis. The designed PEC cytosensor showed a low detection limit of apoptotic cells (as low as three cells), a wide linear range from 1 × 10³ to 5 × 10⁷ cells/mL, and an accurate evaluation of therapeutic effects. It also exhibited good specificity, reproducibility, and stability