Electrochemical immunosensors for interleukin-6. Comparison of carbon nanotube forest and gold nanoparticle platforms

Electrochemical immunosensors based on single wall nanotube (SWNT) forests and 5 nm glutathione-protected gold nanoparticles (GSH-AuNP) were developed and compared for the measurement of human cancer biomarker interleukin-6 (IL-6) in serum. Detection was based on sandwich immunoassays using multiple (14–16) horseradish peroxidase labels conjugated to a secondary antibody. Performance was optimized by effective blocking of non-specific binding (NSB) of the labels using bovine serum albumin. The GSH-AuNP immunosensor gave a detection limit (DL) of 10 pg mL−1 IL-6 (500 amol mL−1) in 10 μL calf serum, which was 3-fold better than 30 pg mL−1 found for the SWNT forest immunosensor for the same assay protocol. The GSH-AuNPs platform also gave a much larger linear dynamic range (20–4000 pg mL−1) than the SWNT system (40–150 pg mL−1), but the SWNTs had 2-fold better sensitivity in the low pg mL−1 range.