Background and Aim: The applications of various nanoparticles as antimicrobial agents in safety and security of food are predicted to grow rapidly in the coming years especially in food packaging and disinfection. However, side effects of NPs usage are not completely realized. Therefore in this study a lux-marked E.coliSM10 S1 biosensor was used to investigate the effect of different concentrations of selenium and silver nanoparticles on bacterial survival and activity at lettuce. Matrial and Methods: Selenium and silver nanoparticles solution of 50 and 100ppm were prepared and autoclaved at 100 ° C for 30 min. Pieces of lettuce were sterilized with a 5% solution of sodium hypochlorite and each sample was inoculated with 107 to 108lux-marked E.coliSM10 S1 culture medium. Then lettuce pieces were placed in 50 and 100ppm of silver and selenium nanoparticles solutions for 5, 10 and 15 minutes time intervals. Samples were transferred to flasks containing 10 ml of alkaline PBS buffer and incubated for 45 minutes at 150 rpm. Samples were then centrifuged at 10,000 rpm for 9 minutes and pellet obtained was dissolved in 450 ml phosphate buffer. Thereafter, 10 l of remaining solution was used for two measurements, one of them was determination of luminescence light output using luminometer and another was counting colonies by micro colony method. Results: Silver nanoparticles concentration of 50 ppm, in time intervals of 5, 10 and 15 minutes declined the number of bacteria(cfu) to 90, 99 and 99% respectively while the light emition (RLU/s) decreased to 43, 68 and 95% respectively. At presence of 100 ppm silver NP the number of bacterial colonies was declined to 98, 99 and 99% respectively and light output lowered to 70, 78 and 95% respectively. No significant effect on bacterial count and luminescence light output were observed when 50 and 100 ppm selenium NPs concentrations were applied. Conclusion: According to the results of the colony counts and luminescence light output samples, Silver NPs even in short time had a significant effect on survival and activity of E.coliSM10 S1 on lettuce. But Selenium NPs even in high concentrations did not have a significant antibacterial activity, therefore could not be recommended as a suitable disinfectant. Further investigation on safety of silver NPs for usage as vegetable disinfectant has to be proceeded.

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