Label-free electronic detection of interleukin-6 using horizontally aligned carbon nanotubes

A facile, sensitive, and label-free assay for detection of interleukin-6 (IL-6) using liquid-gated field-effect transistor (FET) sensors based on horizontally aligned single-walled carbon nanotubes (SWCNT) is proposed. This approach relies on the drain current (Id) responses of the transistor upon interactions of IL-6 with its corresponding antibody (IL-6R) immobilized on SWCNT. The proposed immunosensor exhibits superior sensitivity (limit-of-detection = 1.37 pg/mL) in virtue of the reduced tube-to-tube contact resistance, good selectivity (no responses to bovine serum albumin and cysteine were observed and detection of target molecules in serum was achieved) as a result of the highly specific interaction between IL-6 and IL-6R, and excellent stability (no significant degradation in the electronic performance after storage under ambient conditions for up to 3 months) in virtue of the strong adhesion of CNT to the quartz substrate and good horizontal alignment of these tubes. Therefore, the proposed immunosensor is a promising platform for early diagnosis of various diseases (including some cancers) that can be indicated by the circulating level of IL-6.