Nanoparticles and Efficient Sterilization of Bacterial Samples

1. Nanoparticles and Efficient Sterilization of Bacterial Samples Amanda Svendsen, Beverly Harris, Nin Dingra, Joyce Chow, Brandon Lawson, Will E. Lynch, and Delana A. Nivens, Department of Chemistry, Armstrong Atlantic State University, 11935 Abercorn Street, Savannah, GA 31419, amanda_svendsen06@yahoo.com

2. Introduction • Nanoparticles • can be used to remove contaminants by photocatalysis • are semiconductors

3. Semiconductors

4. Photocatalytic oxidation Figure 1. Example of photocatalytic oxidation on a semiconductor particle

5. Semiconductor + hv  e-CB + h+VB • O2 + e-  O2- (reaction 1) • h+ +H2O  OH▪ + h+ (reaction 2) • O2- + h+ HO2▪ (reaction 3) • HO2▪ + h+ + e- H2O2 (reaction 4) • H2O2 + hv  2OH▪ (reaction 5) Figure 2. Reactions that occur on the surface of nanoparticles that allow for oxidation/reduction reactions to occur

6. Possible mechanism-lipid oxidation Initiation - RH + O2 R▪ + ▪OH Propagation- R▪ + O2  ROO▪ -ROO▪ + RH  R▪ + ROOH -ROOH  RO▪ + HO▪ Termination- R▪ + R▪  RR -R▪ + ROO▪  ROOR - ROO▪ + ROO▪  ROOR + O2

7. Procedure • Nanoparticles of cerium oxide, magnesium oxide, nickel(II) oxide, tungsten(VI) oxide, titanium(IV) oxide, and indium tin oxide were purchased and used as received. • CdS with cystine and molybdenum(IV) disulfide nanoparticles were prepared in the lab

8. Preparation of CdS with cystine • Soln A: 50 mL of CdSO4 (1.0M) or Cd(NO3)2 (1.0 M) in 0.1 M HCl • Soln B: 100 mL of 0.25 M cystine in a 1 M tris buffer (pH=8.6) • A solution was made with a 2:1 ratio of Soln B: Soln A • Na2S (1.0 M) was added by titration (2.5 Na2S :1 Cd ratio) • Centrifuge at 3500 rpm - three times – each time the water was decanted and rinsed with DI-water

9. Preparation of Molybdenum (IV) disulfide • Into a round bottom flask, 4% dioctylsulfosuccinate (1.72 g) was dissolved in xylene (50 mL) using heat while bubbling Argon • Once the solution reached 100 ºC , Mo(CO)6 (113 g) and sulfur (0.0141 g) were added • Refluxed for an hour • Dried in oven • Suspended in DI water

10. Procedure cont. • Samples were prepared with a 1:1 ratio in duplicate (mL of nanoparticle soln: mL of E. coli) • One sample was exposed to all wavelengths of light greater than 400 nm and the second was not exposed to any light • Various exposure time trials (30 min, 1 hour, 2 hour, and 24 hours) • Solutions were then diluted, plated and incubated for 24 hours • The number of bacteria that remained in the sample could then be determined

11. Results and Discussion • Wavelength selection– why 400 nm and above?

12. % of E. Coli Killed, No light Exposure

13. % of E. Coli Killed, Sulfide Nanoparticles and Light

14. % E. Coli Killed,Exposed to Light and Oxide Nanoparticles

15. Results

16. % E. Coli Killed Overall Picture

17. Conclusion • There was an observed increase in the percentage of bacteria killed in the presence of the nanoparticles when compared to only distilled water • There was an observed increase in the percentage of bacteria killed in the presence of nanoparticles exposed to visible light when compared to not being exposed • Further study

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20. Questions???