A label-free electrochemical impedance spectroscopy (EIS) biosensor for the sensitive determination and discrimination of alpha-fetoprotein (AFP) was developed by employing wheat-germ agglutinin (WGA) lectin as molecular recognition element. The EIS biosensor was fabricated by adsorbing carboxyl-functionalized single-wall carbon nanotubes (SWNTs) onto a screen-printed carbon electrode (SPCE) and subsequently covalently coupling WGA onto the surface of the SWNTs-modified electrode. Upon binding of AFP to the biosensor, the electron transfer resistance was increased and the increase in the electron transfer resistance was linearly proportional to the logarithm of the concentration of AFP in the range from 1 to 100 ng/L with a detection limit of 0.1 ng/L. It was found that the employment of SWNTs as immobilization platform could reduce the background and enhance the EIS response. Moreover, the lectin-based biosensor array fabricated with different lectins was used to evaluate the glycan expression of AFP N-glycan and discriminate AFP between healthy and cancer patients serum samples. This work demonstrates that the employment of carbon nanotubes as immobilization platform and lectin as molecular recognition element in biosensor array is a promising approach for the determination and discrimination of glycoproteins for cancer diagnosis. The strategy proposed in this work could further be used for high-throughput, label-free profiling of the glycan expression of cancer-related glycoproteins and to develop methods for cancer diagnosis in the early stages.
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