Electrochemical detection of caspase-3 based on a chemically modified M13 phage virus

Caspase-3, a cysteine-dependent protease, is considered a reliable molecular biomarker for the diagnosis and prognosis of apoptosis-related diseases. In this study, we demonstrated a phage-based electrochemical biosensor for the evaluation of cell apoptosis by the sensitive and specific detection of caspase-3. Specifically, for screening of affinity peptide-displayed phages, phage display was performed using M13 phage libraries (cyclic forms of peptides), and we identified potential affinity peptide-displayed phage clones with the sequence CPTTMWRYC. After characterization of its binding affinity using enzyme-linked immunosorbent assay, whole phage particles were covalently attached to a gold surface using coupling chemistry (MUA-EDC/NHS). The developed phage sensor was characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), electrochemical analysis using cyclic voltammetry (CV), and square wave voltammetry (SWV). Under optimal conditions, the affinity peptide-displayed phage sensor showed a good binding affinity (K_d = 0.13 ± 0.56 μM) and limit of detection (0.39 μM) for caspase-3 detection. Furthermore, developed phage sensor could be monitored the response of apoptotic HeLa cells by detecting caspase-3 activity. This work should stimulate the development of efficient alternative caspase-3 detection methods for the diagnosis and prognosis of apoptosis-related diseases.