Simple and rapid preparation of red fluorescence and red color S. aureus derived nanobioparticles for pathogen detection

In this study, a simple and rapid method was developed to transform protein A producing Staphylococcus aureus cells into red color and red fluorescent nanobioparticles, which were homogeneous, dispersive and relatively stable with a uniform size of 800 nm. The method consists of reaction with a monotetrazolium redox dye at 25 °C for 15 min and heat inactivation at 65 °C for 30 min. This method provided the first S. aureus nanobioparticles with the dual property of red color and red fluorescence. Attributed to the IgG binding site known as protein A on their surface, the nanobioparticles could be used as vectors for immunoassays of many bacteria and viruses. Coagglutination test of Escherichia coli O157:H7 observed by naked eyes showed that the detection limitation of the nanobioprobes was 1 ∗ 106 CFU/ml, which was about 100 times more sensitive than the natural uncolored S. aureus bioprobes. Red fluorescence detection and analysis of the coagglutination product by a microplate reader lowered the detection limit to 2.5 ∗ 104 CFU/ml.