Magnetic MOF-Assisted Radical Polymerization Signal Amplification in Homogeneous System for Ultrasensitive PEC-EC Dual-Mode Detection of Caspase-3 Activity

Enhancing detection sensitivity and reliability is critical in analytical chemistry, particularly for disease diagnosis and biological analysis. Innovative radical polymerization signal amplification strategies, integrated with dual-mode sensing approaches, offer promising avenues for highly sensitive and reliable photoelectrochemical (PEC)-based biosensing. Herein, a novel ultrasensitive PEC-electrochemical (EC) dual-mode biosensing platform was developed for detecting a model analyte of caspase-3, leveraging magnetic metal–organic framework (MOF)-assisted radical polymerization signal amplification in a homogeneous system. Specifically, a magnetic MOF material of MB-UiO-66-NH2 (mMOFs) was employed to load abundant chain-transfer agent (4-cyano-4-(phenylcarbonothioylthio)pentanoic acid, CPAD) to form mMOFs-CPAD, which was immobilized on a 96-well microplate via caspase-3-specific peptides (DEVD peptides). Upon caspase-3 recognition, the DEVD peptides experienced enzymatic cleavage, releasing mMOFs-CPAD. Following magnetic separation, the released mMOFs-CPAD served as a scaffold for grafting poly(ferrocenylmethyl methacrylate) (PFcMMA), thus forming the mMOFs/PFcMMA composite via reversible addition–fragmentation chain-transfer (RAFT) radical polymerization in a homogeneous system. The mMOFs/PFcMMA composite not only effectively suppressed the photocurrent of MWCNTs/PTCA/CdS-modified electrode for PEC assay but also generated an enhanced electrochemical signal for EC assay. Based on the bifunctional polymeric signal probe, the PEC-EC dual-mode biosensing platform exhibited a wide linear detection range of 10–17–10–8 g mL–1 (PEC/EC) and ultralow detection limits of 1.8 ag mL–1 (PEC) and 5.1 ag mL–1 (EC) for ultrasensitive caspase-3 detection. This work pioneers the utilization of RAFT radical polymerization for improving sensitivity and reliability in PEC-based multimode biosensing technologies.