Synthesis of epitope-imprinted magnetic nanoparticles via reverse microemulsion-based interface imprinting strategy for specific extraction of chlorogenic acid and caffeic acid from Chinese medicinal formulae

Chlorogenic acid and caffeic acid are the main active components that exhibit a clearing heat-toxin effect in Chinese medicinal formulae (CMF). However, they have very low content and coexist with many structural analogues and a large number of interfering substances in complex CMF samples, making it difficult to effectively separate and analyze them. Herein, we synthesized epitope-imprinted magnetic nanoparticles (EIMNPs) using a reverse microemulsion-based interface imprinting strategy for specific extraction of chlorogenic acid and caffeic acid from CMF. A dual surfactant reverse microemulsion system was constructed by cetyltrimethylammonium bromide (CTAB) and Triton X-100. Caffeic acid as an epitope template for chlorogenic acid was confined to the oil/water interface through electrostatic attraction between its carboxyl anion and the quaternary ammonium salt cation of CTAB. Hydrophilic polyethylene glycol-coated Fe 3 O 4 magnetic nanoparticles served as substrates. Aminopropyltriethoxysilane, 3-ureidopropyltriethoxysilane, and benzyltriethoxysilane as functional monomers and tetraethyl orthosilicate as a crosslinker were selected. The prepared EIMNPs exhibited excellent specificity for chlorogenic acid and caffeic acid, and their imprinting factors were 4.5 and 6.6, respectively. In addition, the EIMNPs had rapid magnetic separation property and a fast equilibrium time. The EIMNPs-based affinity extraction coupled with high performance liquid chromatography had been successfully applied to the determination of chlorogenic acid and caffeic acid in a Dachaihu decoction, and their limit of detections were 0.6 ng/mL and 0.3 ng/mL, respectively. Compared with other imprinting materials, the EIMNPs had significant advantages in imprinting performance and detection sensitivity, and will play an important role in the study of active components in CMF.