Rapid and low-cost biosensor for the detection of Staphylococcus aureus.

Staphylococcus aureus (S. aureus) is one of the most common etiological agents in hospital-acquired infections and food-borne illness. S. aureus toxins and virulence proteases often circulate in host blood vessels leading to life-threatening diseases. Standard identification approaches include bacterial culturing method, which takes several days. Other nucleic acid-based methods were expensive and required trained personnel. To surmount these limitations, a paper-based biosensor was developed. The sensing mechanism was based on the proteolytic activity of S. aureus proteases on a specific peptide substrate, sandwiched between magnetic nanobeads and gold surface on top of a paper support. An external magnet was fixed on the back of the sensor to accelerate the cleavage of the magnetic nanobeads-peptide moieties away from the sensor surface upon test sample dropping. The colour change resulting from the dissociation of the magnetic nanobeads moieties was detected by the naked eye and analysed using ImageJ analysis software for the purpose of quantitative measurement. Experimental results showed detection limits as low as 7, 40 and 100 CFU/mL for S. aureus in pure broth culture, and inoculated in food produces and environmental samples, respectively upon visual observation. The specificity of the sensor was examined by blind testing a panel of food-contaminating pathogens (Listeria monocytogenesis 19115 and E. coli O157:H7), clinical isolates (methicillin-resistant S. aureus (MRSA) and Candida albicans) and standard (Pseudomonas aeruginosa 15692) pathogens. Negative read-out was observed by the naked eye for all tested isolates except for MRSA. Moreover, this sensing tool requires minute's time to obtain the results. In conclusion, this sensing platform is a powerful tool for the detection of S. aureus as a potential point-of-care diagnostic platform in hospitals and for use by regulatory agencies for better control of health-risks associated with contaminated food consumption.