(813b) Ultrasensitive Detection of Enteric Fever Using Magnetic Nanoparticles: Evanescent Wave Optical Illumination Studies

An ultrasensitive method for early stage detection of Salmonella is demonstrated using total internal reflection fluorescence (TIRF) microscopy. Salmonella is captured from the milliliters volumes of spiked serum samples using fluorescent magnetic nanoparticles conjugated with anti-Salmonella. The labeled cells are separated from the unbound nanoparticles by simple gravity-based settling in confined volumes, circumventing the use of bulky ultracentrifuges. Thus the fluorescent magnetic nanoparticle conjugates serves both as pathogen preconcentrators and biosensing reagents. The fluorescently-labeled cells are selectively imaged at the bottom of the substrate by evanescent wave illumination using a TIRF microscope. Simultaneously the amount of cells captured was calculated by using plating method in order to validate the captured cells observed under the microscope. This technique allows rapid visualization of both live and dead bacterial cells unaffected by the antimicrobial properties of fresh blood and the presence of antimicrobial agent in the blood (in case of pretreatment with antibiotics). The current known methods for enteric fever diagnosis using cell culture often have low sensitivity and specificity, and long turnaround times. Thus, because of high sensitivity and rapid detection of pathogens the proposed approach could be very promising in the field of diagnostics, unlocking many biomedical opportunities.