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Rapid electrochemical detection of Staphylococcus aureus based on screen-printed gold electrodes modified with cysteine and Guinea grass (Panicum maximum) peroxidase

We present a novel electrochemical method for a rapid analytical detection of Staphylococcus aureus in culture and spiked milk samples through hydrogen peroxide (H2O2) consumption on a screenprinted gold electrode (SPGE) modified with cysteine and peroxidase from Guinea grass leaves (GGP). This peroxidase (POD) had a specific activity of 470 U mg-1 and it was immobilized on an SPGE surface previously modified with cysteine. Cyclic voltammograms of gold electrodes modified with peroxidase and cysteine in the presence of potassium ferrocyanide as a redox probe demonstrated an increase of approximately 5% in the current compared to the bare gold electrode. The SPGE modified electrode exhibited a good electrocatalytic response towards H2O2 reduction. We added a constant H2O2 concentration of 1x10-3 M to the culture medium and measured the decrease in the H2O2 current at -780 mV consumed by catalase from S. aureus. Our modified electrode proved to sense S. aureus in a range concentration between 3x102 and 3x108 CFU/mL-1 with a detection limit of 102 CFU/mL-1, detection time of about ~20 min, and a sensitivity of 0.020 mA CFU-1.