Design of an RSM-optimized magnetic–fluorescent nanoprobe utilizing geothermal silica for enhanced bacterial sensing

In this study, we synthesized a magnetic fluorescent silica nanocomposite (MFSNc) using a controlled modified sol-gel method for sensitive recognition of Staphylococcus aureus (SA) bacteria. The effects of rhodamine B concentration, Si/Fe ratio, and percentage of cetyltrimethylammonium bromide (CTAB) on the fluorescence intensity, magnetic saturation, and specific surface area, respectively, were statistically optimized using the Box-Behnken Design within the framework of response surface methodology (RSM). This resulted in an optimized value of 5 mg g^-1, 0.5 g g^-1, and 3% of rhodamine B concentration, Fe/Si ratio, and CTAB, respectively. The RSM-optimized MFSNc generated enhanced intrinsic properties, i.e., a high fluorescence intensity of 566.20 a.u. at 583.97 nm, a magnetic saturation of 16.70 emu g^-1, and a specific surface area of 139.45 m² g^-1. The MFSNc sample was further modified with vancomycin and applied as a biosensing platform to detect the presence of SA bacteria. After 25 minutes of incubation time, the fluorescence intensity obtained before and after SA detection was 42.59 a.u and 4.60 a.u., respectively, obtaining a decrease of intensity (%I_loss) of 89.20%. A linear relationship between %I_loss and the SA concentrations from 10⁰ to 10⁸ CFU mL^-1 was observed with LOD calculated to be 5.08 CFU mL^-1. The sensitivity of the RSM-optimized MFSNc in detecting SA bacteria makes it suitable for applications in clinical diagnostics, food safety, and environmental monitoring.