Rapid, highly sensitive and quantitative detection of interleukin 6 based on SERS magnetic immunoassay

Sepsis is a systemic inflammatory response syndrome caused by infection, and is a common disease in intensive care units (ICUs), whereby the mortality rate is as high as 30% to 50%. Early diagnosis and treatment can significantly reduce the mortality rate of patients with sepsis. We have developed a method based on SERS for the rapid and quantitative detection of IL-6. Using the principle of double antibody sandwich, the core-shell nanoparticles embedded with a Raman reporter (Au@4MBA@Ag NPs) are coupled to the tracer antibody, while the biotin was coupled to the capture antibody to form an antibody-antigen-antibody sandwich structure with the antigen during detection of the structure. Streptavidin (SA) and biotin had a strong affinity, and the sandwich structure was captured by SA magnetic beads and detected by Raman spectroscopy under the enrichment of an external magnetic field. The results showed a good linear relationship between the Raman signal and the concentration of IL-6 in the concentration range of 0-1000 pg mL-1 (r = 0.9997) with a limit of detection of 1.6 pg mL-1. Also, the recovery rate of standard addition was 93.9-99.1%, and the coefficient of variation intra-assay and inter-assay of the three batches of reagents was less than 15%. Furthermore, it showed excellent specificity with procalcitonin (PCT, 20 ng mL-1) and C-reactive protein (CRP, 100 μg mL-1) and had no cross-reactivity. Except for bilirubin (2 mg mL-1) and hemoglobin (10 mg mL-1), other common interferences in the serum did not interfere, showing good anti-interference performance. Moreover, 57 clinical serum samples were detected via the chemiluminescence method simultaneously, and the detection results showed a good correlation (R2 = 0.9793, P < 0.01). There was no significant difference between the two performances (P > 0.05). The proposed method has numerous advantages such as high sensitivity, wide linear range, short detection time and simple operation, which provide a new technical reference for the clinical detection of sepsis biomarkers.