An electrochemical impedance sensor for the label-free ultrasensitive detection of interleukin-6 antigen

A simple impedimetric immunosensor was developed for ultrasensitive detection of interleukin-6 (IL-6) antigen. The sensing platform integrated two substrates that had previously been employed individually to detect IL-6. This was constructed by electrochemically depositing Au nanoparticles on horizontally aligned single walled carbon nanotube array that has been in situ prepared on a SiO2/Si substrate. The as-prepared immunosensor was able to detect IL-6 antigen in serum at a low limit of 0.01 fg mL−1, which was greatly lower than the detection limit reported with carbon nanotube forest or Au nanoparticles alone and was also significantly lower than that seen in a healthy individual. The sensor has a wide linear response range from 0.01 to 100 fg mL−1 and also exhibits low responses to a number of interferents that were found in serum. The sensor has a high stability and its sensitivity does not change after being stored at 4 °C for a month.