Sensitivity Improvement in Electrochemical Immunoassays Using Antibody Immobilized Magnetic Nanoparticles with a Clean ITO Working Electrode

We report a dramatic improvement in the detection sensitivity of electrochemical immunosensors through the use of a magnetic nanoparticle for immunoassay reactions and an ITO working electrode for measurement of the electrochemical enzymatic reaction signals. In general, electrochemical sensors developed for immunoassay require the immobilization of capture antibodies on the surface of the working electrode. Under these circumstances, the working electrode comes into direct contact with various biological samples, and unwanted non-specific binding inevitably interferes with the detection signal. Moreover, chemical surface treatment of the working electrode to immobilize capture antibodies degrades the quality of the electrochemical signals during target determination. Here, we address these issues by immobilizing capture antibodies on the surface of magnetic nanoparticles and separating the surface for measurement of electrochemical signals from the immune reactions. By avoiding direct contact with biological materials, the surface of the working electrode could not be contaminated and could be maintained clean. We also provide experimental evidence that these novel immunoassay platforms benefit from a reduction in the noise signal. Indeed, the signal-to-noise ratio, an essential characteristic of quantitative detection, could be improved by approximately 11.8-fold compared with the electrochemical immunoassay of conventional surface modification approach, while retaining an excellent coefficient of variation (≤ 18%). The method was applied to the practical immunosensing for matrix met-alloproteinase-9 (MMP-9), the bladder cancer marker in the urine, and exhibited excellent performance.