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

Abstract

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.