Quantification of Interleukin-6 in cell culture medium using surface plasmon resonance biosensors

Interleukin (IL)-6, a multifunctional cytokine, is widely used as an index for illnesses such as inflammatory and autoimmune disorders, coronary artery disease, neurological disease, and gestational problems. It is thus very important to be able to precisely quantify the level of IL-6 for disease diagnosis and any subsequent therapy. Surface plasmon resonance (SPR) biosensors are sensitive in detecting the interaction between biomolecules by sensing the changes in the refractive index on the sensor chip. This study investigated the SPR technique to determine the IL-6 secretion of human fibroblast MRC5-CVI cells induced by lipopolysaccharide (LPS). To reduce non-specific binding, a mixed self-assembled monolayer of mercaptoundecanoic acid (MUA) and mercaptohexanol (MCH) was attached to the sensor, and then used for IL-6 determination using a sandwich type immunoassay. In addition, two antibody immobilization methods were applied to the sensor surface-direct immobilization and indirect immobilization via protein G affinity. The results demonstrated that the direct immobilization method had a better antibody binding capacity on the sensor surface. The level of cellular IL-6 secretion detected by the SPR biosensor showed a consistent correlation with the commercial kit of IL-6 enzyme-linked immunosorbent assay.