Preparation of a pipette tip-based molecularly imprinted solid-phase microextraction monolith by epitope approach and its application for determination of enkephalins in human cerebrospinal fluid

Abstract

In this study, a novel molecularly imprinted polymer (MIP) monolith for highly selective extraction of enkephalins was synthesized and prepared in a micropipette tip using epitope imprinting technique. The synthesized MIPs were characterized by scanning electron microscope (SEM) and infrared spectroscopy. A molecularly imprinted solid-phase microextraction (MISPME) method was developed for extraction of enkephalins in aqueous solutions. The parameters affecting MISPME were optimized. The results indicated that this MIP monolith exhibited specific recognition capability, high enrichment efficiency and excellent reusability for enkephalins. MALDI-TOF MS analysis demonstrated that this MIP monolith can act as a useful tool for highly selective purification and enrichment of enkephalin, a kind of low abundance protein, from high-abundance proteins in human cerebrospinal fluids (CSF). Employed this MIP monolith as solid-phase microextraction column, quantitative assay of enkephalins in human CSF was developed by HPLC–ultraviolet (UV) detection in this work. The detection limits were 0.05–0.08nM. This MISPME/HPLC–UV method was used to quantify Met-enkephalin and Leu-enkephalin levels in the CSF of patients with cancer pain.