Hemin-catalyzed SI-RAFT polymerization for thrombin detection

Ultrasensitive protein detection has considerable potential for early diagnosis and screening of diseases. Here, based on Hemin-catalyzed surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization, this work developed an assay for ultrasensitive fluorescent biosensing of proteins and established a thrombin fluorescent sensor. First, the amino-modified aptamer 1 was immobilized on Fe 3 O 4 magnetic beads, and then thrombin was added to form the aptamer 1-thrombin bioaffinity complex. Another thiol-modified aptamer 2 binds to bound thrombin to form a sandwich structure. Fluorescein O-methacrylate was used as the monomer, acetylacetone (ACAC) as the initiator, and Hemin as the catalyst. Through Hemin-catalyzed SI-RAFT polymerization, a large number of thrombin molecules are labeled with fluorescein O-methacrylate, resulting in severalfold amplification of the fluorescent signal. By detecting the fluorescent signal in thrombin from 1.0 fM to 0.1 nM, the proposed super sandwich strategy can detect thrombin at 0.98 fM, which is lower than the detection limit of most other methods.