Combined application of sub-toxic level of silver nanoparticles with low powers of 2450 MHz microwave radiation lead to kill Escherichia coli in a short time


1 Department of Pharmaceutical Biotechnology, Faculty of Pharmacy and Biotechnology Research center, Tehran

2 Iran Nanotechnology Initiative Council, Tehran, Iran

3 Department of Biotechnology, St. Michael College of Engineering and Technology, Kalayarkoil, India

4 Department of Pharmaceutical Biotechnology, Faculty of Pharmacy and Biotechnology Research center, Tehran University of Medical Sciences, Tehran, Iran


Electromagnetic radiations which have lethal effects on the living cells are currently also considered as a disinfective physical agent.
Materials and Methods:
In this investigation, silver nanoparticles were applied to enhance the lethal action of low powers (100 and 180 W) of 2450 MHz electromagnetic radiation especially against Escherichia coli ATCC 8739. Silver nanoparticles were biologically prepared and used for next experiments. Sterile normal saline solution was prepared and supplemented by silver nanoparticles to reach the sub-inhibitory concentration (6.25 μg/mL). Such diluted silver colloid as well as free-silver nanoparticles solution was inoculated along with test microorganisms, particularly E. coli. These suspensions were separately treated by 2450 MHz electromagnetic radiation for different time intervals in a microwave oven operated at low powers (100 W and 180 W). The viable counts of bacteria before and after each radiation time were determined by colony-forming unit (CFU) method.
Results showed that the addition of silver nanoparticles significantly decreased the required radiation time to kill vegetative forms of microorganisms. However, these nanoparticles had no combined effect with low power electromagnetic radiation when used against Bacillus subtilis spores.
The cumulative effect of silver nanoparticles and low powers electromagnetic radiation may be useful in medical centers to reduce contamination in polluted derange and liquid wastes materials and some devices.


1. Bao Q, Zhang D, Qi P. Synthesis and characterization of silver nanoparticle and graphene oxide nanosheet composites as a bactericidal agent for water disinfection. J Colloid Interface Sci 2011; 360: 463-470.
2. Tonuci LRS, Paschoalatto CFPR, Pisani R. Microwave inactivation of Escherichia coli in healthcare waste. Waste Manage 2008;.28:840-848.
3. Pellerin C.Alternatives to Incineration: There's More Than One Way to Remediate. Environ Health Persp. 1994; 102: 840-845.
4. Diaz LF, Savage GM, Eggerth LL. Alternatives for the treatment and disposal of healthcare wastes in developing countries. Waste Manage. 2005; 25: 626-37.
5. Dunnick JK, Melnick RL. Assessment of the carcinogenic potential of chlorinated water: experimental studies of chlorine, chloramine, and trihalomethanes. J Natl Cancer Inst. 1993; 817-822.
6. Mollazadeh-Moghaddam K, Moradi BV, Dolatabadi-Bazaz R, Shakibae M, Shahverdi AR. An enhancing effect of gold nanoparticles on the lethal action of 2450 MHz electromagnetic radiation in microwave oven. Avi J Med Biotechnol. 2011; 3: 195-200.
7. Sekhon BS, Kamboj SR. Inorganic nanomedicine--part 2. Nanomed Nanotech Biol Med. 2010; 6: 612-618.
8. Sheng Z, Liu Y. Effects of silver nanoparticles on wastewater biofilms. Water Res. 2011; 45: 6039-6050.
9. Duncan TV. Applications of ano technology in food packaging and food safety: barrier combined effect of Ag NPs with microwave radiation materials, antimicrobials and sensors. J Colloid Interface Sci. 2011; 363 (1): 1-24.
10. Kathiresan K, Manivannan S, Nabeel MA, Dhivya B. Studies on silver nanoparticles synthesized by a marine fungus, Penicillium fellutanum isolated from coastal mangrove sediment. Colloids Surfaces B. 2009; 71: 133-137.
11. Martinez-Gutierrez F, Olive PL, Banuelos A, Orrantia E, Nino N, Sanchez EM, Ruiz F, Bach H, Av-Gay Y. Synthesis, characterization, and evaluation of antimicrobial and cytotoxic effect of silver and titanium nanoparticles. Nanomed Nanotech Biol Med. 2010; 6: 681-688.
12. Beer C, Foldbjerg R, Hayashi Y, Sutherland DS, Autrup H. Toxicity of silver nanoparticles-nanoparticle or silver ion? Toxicol Lett. 2012; 208: 286-292.
13. Yen HJ, Hsu SH, Tsai CL. Cytotoxicity and immunological response of gold and silver nanoparticles of different sizes. Small. 2009; 5: 1553-1561.
14. Hsin YH, Chen CF, Huang S, Shih TS, Lai PS, Chueh PJ. The apoptotic effect of nanosilver is mediated by a ROS- and JNK-dependent mechanism involving the mitochondrial pathway in NIH3T3 cells. Toxicol Lett. 2008; 179: 130-139.
15. Wise JP, Sr., Goodale BC, Wise SS, Craig GA, Pongan AF, Walter RB, Thompson WD, Ng AK, Aboueissa AM, Mitani H and others. Silver nanospheres are cytotoxic and genotoxic to fish cells. Aquat Toxicol. 2010; 97: 34-41.
16. Najdovski L, Dragas AZ, Kotnik V. The killing activity of microwaves on some non-sporogenic and sporogenic medically important bacterial strains. J Hosp Infect. 1991; 19: 239-247.
17. Sahin A, Eiley D, Goldfischer ER, Stravodimos KG, Zeren S, Isenberg HD, Smith AD. The in vitro bactericidal effect of microwave energy on bacteria that cause prostatitis. Urology. 1998; 52: 411-415.
18. Mokhtari N, Daneshpajouh S, Seyedbagheri S, Atashdehghan R, Abdi K, Sarkar S, Minaian S, Shahverdi HR, Shahverdi AR. Biological synthesis of very small silver nanoparticles by culture supernatant of Klebsiella pneumonia: The effects of visible-light irradiation and the liquid mixing process. Mater Res Bull. 2009; 44: 1415-1421.
19. Shahverdi AR, Fakhimi A, Shahverdi HR, Minaian S. Synthesis and effect of silver nanoparticles on the antibacterial activity of different antibiotics against Staphylococcus aureus and Escherichia coli. Nanomed Nanotech Biol Med. 2007; 3: 168-171.
20. M.Andrews J. Determination of minimum inhibitory concentrations. J Antimicrob Chemother. 2001; 48: 5-16.
21. Rohrer MD, Bulard RA. Microwave sterilization. J Am Dent Assoc. 1985; 110: 194-198.
22. Rohrer MD, Terry MA, Bulard RA, Graves DC, Taylor EM. Microwave sterilization of hydrophilic contact lenses. Am J Ophthalmol. 1986; 101 :49-57.
23. Goldblith SA, Wang DI. Effect of Microwaves on Escherichia coli and Bacillus subtilis. Appl Microbiol. 1967; 15: 1371-1375.