An innovative electrochemical immunosensor based on nanobody heptamer and AuNPs@ZIF-8 nanocomposites as support for the detection of alpha fetoprotein in serum

A novel electrochemical immunoassay based on nanobody heptamer for ultrasensitive detection of alpha fetoprotein (AFP) is proposed. First, AFP heptamer fusion protein (A1-C4bp alpha) is prepared via fusing the AFP-specific nanobody (A1) with the C-terminal fragment of C4-binding protein (C4bp alpha). Then A1-C4bp alpha heptamer with higher affinity is used as the molecule recognizing probe to capture numerous the AFP, increasing the sensitivity of the immunosensor. Moreover, AuNPs decorated zeolitic imidazolate framework (AuNPs@ZIF-8) with large surface area, and abundant binding sites serves an ideal nanocarrier to increase heptamer loading. Multiwalled carbon nanotube (MWCNTs) with excellent electrical conductivity was immobilized on glassy carbon electrode (GCE) to enhance electrochemical signals. The coupling between the AuNPs@ZIF-8@MWCNTs and heptamer technologies constructed an ultrasensitive and specific immunosensor for AFP detection in the range of 0.1 to 105 pg mL(-1) with a lower detection limit of 0.033 pg mL(-1). The as-prepared electrochemical sensing exhibited excellent performance and could be employed to determine AFP with satisfactory results in actual serum samples, suggesting that the proposed strategy for nanobody multimerization provides an alternative scheme for enhancing sensitivity in important biomarkers detection.