A molecularly imprinted copolymer based electrochemical sensor for the highly sensitive detection of L-Tryptophan

A novel L-tryptophan (L-Trp) electrochemical sensor is fabricated, which is based on the molecularly imprinted copolymer (MIP) of dual -functional monomers and ionic liquid (i.e. 1-butyl-3-methylimidazolium hexafluorophosphate) functionalized multi-walled carbon nanotubes (MWCNTs@IL). The MWCNTs@IL is prepared via ion exchange, while the MIP is synthesized by using L-Trp as template, styrene and 4-vinylbenzoic acid as functional monomers, Triton X-100 as emulsifier, 1, 2-divinylbenzene as cross-linking reagent and K₂S₂O₈ as initiator. Prior to copolymerization the functional monomer 4-vinylbenzoic acid is combined with the template molecule by forming amide bond. The template molecule is eluted by hydrolysis, and rebound by electrostatic, hydrogen-bond and π-π interaction. To construct L-Trp sensor a little of Nafion is introduced to enhance the stability and to promote rebinding. The resulting sensor Nafion-MIP-MWCNTs@IL/GCE shows a wide linear range (8 nM-26 μM) and a low detection limit (6 nM). It is successfully applied to the determination of L-Trp in oral liquid and human serum samples.