Methylene blue-encapsulated liposome for immobilization-free electrochemical immunoassay of interleukin-6 from nervous headache

Interleukin-6 (IL-6) protects neurons by inhibiting the expression of factors related to neuronal injury in nervous headache patients. The development of rapid and sensitive IL-6 detection methods are very advantageous for easing the pain of the patients. In this work, an immobilization-free immunodetection method is explored for the voltammetric screening of IL-6 in serum samples from nervous headache patients. Initially, methylene blue-encapsulated liposome (MBLS) labeled with anti-IL-6 detection antibodies are confined into anti-IL-6 capture antibody-coated microplate through a sandwich-type immunoreaction, and subsequently subject to lysis treatment. After that, the lytic solution is transferred into a detection cell including Nafion-modified working electrode. Methylene blue molecules with positive charge are captured onto the negatively charged Nafion membrane, thus generating a voltammetric signal. The voltammetric peak currents are relative to the IL-6 amount in the solution. At the optimized experimental situations, MBLS-based split-type electrochemical sensing protocols have acceptable voltammetric currents for IL-6 from 0.01 to 100 pg mL-1, and allow screening of IL-6 as low as a concentration of 9.1 fg mL-1. The batch-to-batch coefficients of variation were ≤11.95%. A good anti-interference capability was acquired against other biomolecules. Seven human serum specimens and two diluted serum samples including IL-6 obtained from nervous headache patients were determined by MBLS-based electrochemical immunoassay, and achieved well-matched results in comparison with those of IL-6 ELISA protocol.