Bilirubin is a metabolite of hemoglobin. Concentration of bilirubin in serum is often regarded as an important physiological indicator for judging the liver disease. In this work, molecularly imprinted polymer (MIP) doped with room-temperature ionic liquid (RTIL) and bilirubin template molecule was fabricated onto the surface of Au electrode. Both methacrylic acid (MAA) and ethylene glycol dimethyl acrylate (EGDMA) were used as the functional monomers. EGDMA was also used as the corsslinker. 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([BMIM][TF2N]) was the chosen RTIL. Together with bilirubin, the bilirubin-imprinted [BMIM][TF2N]-
d-poly(MAA-EGDMA) ([BMIM][TF2N] doped poly(MAA-
co-EGDMA)) was synthesized onto the Au surface. The SEM images showed that the polymeric film thus prepared was rather uniform and the average thickness was approximately 1.98 μm. After the extraction by a proper solvent, most bilirubin (the imprinted template molecule) was removed from the imprinted [BMIM][TF2N]-
d-poly(MAA-EGDMA) film. Consequently, specific binding cavity for bilirubin was created after the extraction. Via which, electrochemical sensing of bilirubin by the amperometric mode owing to the specific interaction of the polymer film with bilirubin template would become feasible.
RTIL could enhance the amperometric signal of the MIP electrode. The imprinting factor of 5.52 ± 0.09 and the detection sensitivity of 0.367 ± 0.019 μA/cm2/mg/dL for bilirubin were achieved, respectively, from the imprinted [BMIM][TF2N]-d-poly(MAA-EGDMA) modified Au electrode. The RTIL doped MIP electrode is even able to detect bilirubin in the low concentration ranging from 0.2 to 1.0 mg/dL. The selectivity of bilirubin against biliverdin was 2.13. Additionally, the MIP electrode could discriminate bilirubin in the presence of serum. In summary, the experimental results confirm the feasibility of the RTIL-MIP electrode for the detection of bilirubin in serum.
Keywords: bilirubin, molecularly imprinted polymer (MIP), room-temperature ionic liquid (RTIL)
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