Transcript Nanoparticles and Efficient Sterilization of Bacterial Samples
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, [email protected]
Introduction
Nanoparticles can be used to remove contaminants by photocatalysis are semiconductors
Semiconductors
Photocatalytic oxidation
Figure 1.
Example of photocatalytic oxidation on a semiconductor particle
Semiconductor + h v O h 2 + O 2 + e O 2 +H 2 O OH ▪ + h HO 2 ▪ + H 2 O 2 + h + h + + e v HO 2 ▪ + h 2OH ▪ H + 2 O 2 e CB + h + VB (reaction 1) (reaction 2) (reaction 3) (reaction 4) (reaction 5)
Figure 2.
Reactions that occur on the surface of nanoparticles that allow for oxidation/reduction reactions to occur
Possible mechanism lipid oxidation
Initiation RH + O 2 R ▪ + ▪ OH Propagation R ▪ + O 2 - ROO ▪ ROO ▪ + RH - ROOH RO ▪ R ▪ + ROOH + HO ▪ Termination R ▪ + R ▪ - R ▪ ROO ▪ RR + ROO ▪ + ROO ▪ ROOR ROOR + O 2
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
Preparation of CdS with cystine
Soln A: 50 mL of CdSO 4 0.1 M HCl (1.0M) or Cd(NO 3 ) 2 (1.0 M) in 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 Na 2 S (1.0 M) was added by titration (2.5 Na 2 S :1 Cd ratio) Centrifuge at 3500 rpm - three times – each time the water was decanted and rinsed with DI-water
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 sulfur (0.0141 g) were added (113 g) and Refluxed for an hour Dried in oven Suspended in DI water
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
Results and Discussion
Wavelength selection– why 400 nm and above?
0.6
0.5
0.4
0.3
0.2
0.1
0 200 TiO CeO NiO2 300 400 wavelength (nm) 500
% of E. Coli Killed, No light Exposure
100% 90% 80% 70% 60% 50% 40% 30% 20% 10% CeO2 Ni Ti Wo3 In CdS Cys M oS2 M gO Water
% of E. Coli Killed, Sulfide Nanoparticles and Light
110% 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% CdS-Cys M oS2 Water 120 minutes 60 minutes 0 minutes
% E. Coli Killed, Exposed to Light and Oxide Nanoparticles
110% 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% CeO2 Ni Ti Wo3 In Water 120 minutes 60 minutes 30 minutes
Results
CeO 2 Ni Ti WO 3 In CdS-cys MoS 2 MgO Water 0.5 hr
65 % 27 % 43 %
± 1 hr ± 2 hr ±
9 % 10 % 93 % 94 % 93 % 49 % 2 % 2 % 5 % 10 % 12 % 88 % 97 % 10 % 4 % 98 99 % 98 % 86 % 83 % 94 % 100 % 2 % 2 % 2 % 10 % 4 % 7 % 0 % 15 % 4 % 39 % 7 % 49 % 8 %
24 hr
96 % 74 % 94 % 95 % 97% 96 %
±
3 % 4 % 0 % 0 % 3 %
Not Exposed
15 % 0 % 26 % 22 % 4 % 23 % 84 % 96 % xxxx
% E. Coli Killed Overall Picture
100% 90% 80% 70% 60% 50% 40% 30% 20% 10% CeO2 Ni Ti Wo3 In CdS Cys M oS2 M gO Water
120 minutes 60 minutes 30 minutes 0 minutes
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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