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Enzyme-Free Amplification Strategy for Biosensing Using Fe3+–Poly(glutamic acid) Coordination Chemistry

Wu, Jing, Xianyu, Yunlei, Wang, Xiangfeng, Hu, Dehua, Zhao, Zhitao, Lu, Ning, Xie, Mengxia, Lei, Hongtao, Chen, Yiping
Analytical chemistry 2018 v.90 no.7 pp. 4725-4732
binding capacity, density functional theory, enzyme-linked immunosorbent assay, iron, metal ions, nanoparticles, point-of-care systems, polyglutamic acid, polystyrenes, shelf life
In this work, we outline a signal amplification strategy using the coordination chemistry between Fe³⁺ and poly(glutamic acid) (PGA) for biosensing applications. The theoretical calculation based on density functional theory shows that PGA has a much higher binding affinity with Fe³⁺ than the other metal ions. Guided by this rationale, we prepare a PGA-mediated signal probe through conjugating PGA onto polystyrene (PS) nanoparticles to form a brushlike nanostructure for Fe³⁺ coordination. This PGA–PS brush (PPB) has a large loading capacity of Fe³⁺ with a number of 1.92 × 10⁸ Fe atoms per nanoparticle that greatly amplifies the signals for assays in an enzyme-free way. Combined with ferrozine coloration-based readout, this PPB-mediated amplification is further applied for the enzyme-free immunoassay that shows an ultrahigh sensitivity for detection of microcystins-LR (12 pg/mL), a 5-fold enhancement compared with that of traditional enzyme-linked immunosorbent assay (ELISA) (60 pg/mL). In addition, the good stability, rapid response, and long shelf life make this enzyme-free amplification strategy a promising platform for point-of-care biosensing applications.