Surface plasmon resonance immunoassay for the detection of the TNFα biomarker in human serum

A simple method for the detection of TNF-alpha protein biomarker in human serum with great sensitivity has been developed using a surface plasmon resonance biosensor. Signal amplification based on a sandwich immunoassay including gold nanoparticles was used. Detection in serum proved to be challenging due to high undesirable non-specific binding to the sensor surface stemming from the matrix nature of the sample. After optimization of the assay parameters and, in the case of serum, of a sample dilution buffer to minimize the non-specific binding, very low limits of detection were achieved: 11.6 pg/mL (211 fM) and 54.4 pg/mL (989 fM) for spiked buffer and human serum respectively. The amplification steps with high affinity biotinylated antibodies and streptavidin-fuctionalized nanoparticles greatly enhanced the signal with the advantage of additional specificity. Due to its simplicity and sensitivity, the immunoassay has proved feasible to be used for detection of low concentration biomarkers in real samples.