Label-free electrochemical immunosensor for the rapid and sensitive detection of the oxidative stress marker superoxide dismutase 1 at the point-of-care

In this work, we have fabricated a label-free electrochemical immunosensor for the detection of Cu,Zn superoxide dismutase (SOD1) which is clinically important to a wide variety of neurodegenerative, cardiovascular, and chronic immune diseases. The immunosensor is comprised of a screen printed carbon electrode (SPCE) modified with self-assembled monolayers (SAMs) of gold nanoparticles (GNPs) in electropolymerized polypyrrole (PPy) and biofunctionalized with monoclonal anti-SOD1 antibody. The morphological changes of each electrode modification step were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) while electrochemical changes were monitored via cyclic voltammetry (CV) and impedance spectroscopy (EIS) by using ferri-ferrocyanide as electrochemical redox probe. The GNP nanostructured immunosensor indirectly monitors the SOD1 levels via electrocatalytic oxidation of nitrite, due to inherent nitrite oxidase activity of SOD1, with a wide linear sensing range (0.5 nM to 5 μM), low detection limit (0.5 nM), and high sensitivity (46.6 ± 3.5 nA nM−1). SOD1 concentration levels were also measured in real biological samples (i.e., cultured human epidermal keratinocytes) and the results correlated well with a western blot densitometry assay. Such rapid detection of SOD1 concentration levels in real biological samples is well-suited for point-of-care (POC) diagnostics.