A dual electrochemical/colorimetric magnetic nanoparticle/peptide-based platform for the detection of Staphylococcus aureus.

Point-of-care facile and economical detection of Staphylococcus aureus (S. aureus), one of the main causes of food-borne illness, is highly demanded for the early diagnosis and control of infections. Herein, inspired by the proteolytic activity of S. aureus protease on a specific peptide substrate, we developed a rapid, simple and cost-effective biosensor for S. aureus using dual colorimetric and electrochemical detection on the same platform. In this approach, gold screen printed electrodes were used on which specific peptide sequences coupled to magnetic nanoparticles were immobilized giving the black color of the sensor surface. The addition of the S. aureus protease solution on the electrode surface causes cleavage of the peptide sequence and the release of the magnetic nanoparticles revealing the golden colour of the electrode which can be easily seen by the naked eye. Furthermore, square wave voltammetric signals can be detected on the same electrode in the ferro/ferricyanide redox couple. The change in the peak current after peptide cleavage was directly proportional to the concentration of S. aureus. The detection limit of the electrochemical assay was 3 CFU ml-1 after 1 min. Moreover, the biosensor was capable of specifically distinguishing S. aureus from other food- and water-borne bacteria such as E. coli and Listeria using the dual mode colorimetric and electrochemical detection. The biosensor was also tested in spiked milk and water samples showing very good recovery percentages. Thus, we believe that this dual mode biosensing platform enables the easy and accurate determination of S. aureus and holds great promise for point-of-care diagnosis.