Label-free electrochemical immunosensors based on surface-initiated atom radical polymerization

A novel label-free immunosensing strategy for sensitive detection of tumor necrosis factor-alpha antigen (TNF-α) via surface-initiated atom transfer radical polymerization (SI-ATRP) was proposed. In this strategy, the Au electrode was first modified by consecutive SI-ATRP of ferrocenylmethyl methacrylate (FMMA) and glycidyl methacrylate (GMA), and TNF-α antibody was coupled to the copolymer segment of GMA (PGMA) by aqueous carbodiimide coupling reaction. Subsequently, the target TNF-α antigen was captured onto the Au electrode surface through immunoreaction. The whole process was confirmed by scanning electron microscopy (SEM) and surface plasmon resonance (SPR) measurements. With introduction of redox polymer segment of FMMA (PFMMA) as electron-transfer mediator, the antigen-coupled Au electrode exhibited well electrochemical behavior, as revealed by cyclic voltammetry measurement. This provided a sensing platform for sensitive detection of TNF-α with a low detection limit of 3.9 pg mL(-1). Furthermore, the "living" characteristics of the ATRP process can not only be readily controlled but also allow further surface functionalization of the electrodes, thus the proposed method presented a way for label-free and flexible detection of biomolecules.