Semi-conductor Nanoparticles for the Photodestruction of Biomolecules Nin Dingra, Joyce Chow, Elizabeth Baker, Juan Aragon, Judy Awong-Taylor, Will E. Lynch, and Delana A. Nivens Department of Chemistry Armstrong Atlantic State University Savannah, Georgia 31419 Dept. of Chemistry and Physics
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Semi-conductor Nanoparticles for the Photodestruction of Biomolecules
Nin Dingra, Joyce Chow, Elizabeth Baker, Juan Aragon, Judy Awong-Taylor, Will E. Lynch, and
Delana A. Nivens Department of Chemistry
Armstrong Atlantic State UniversitySavannah, Georgia 31419
Dept. of Chemistry and Physics
What Are Nanoparticles
• Microscopic particles measured in nanometers
• They are the smallest solids that can to be manufactured
• Do not behave like classical particles, exist in the world of quantum physics.
• Can have very different atomic and molecular properties such as conductivity, hardness, and melting points than bulk materials.
Nanotechnology - study of materials having the following properties :
Dimension: At least one dimension from 1 to 100 nanometer (nm)
Preparation: Designed with methodologies that shows fundamental control over the physical and chemical attributes of molecular-scale structures
Building blocks: They can be combined to form larger structures
Dept. of Chemistry and Physics
Why Do We Study Nanoparticles?• Nanoparticles provide the ability to engineer, control, and
exploit various chemical, physical, and electrical properties
• In the nano-world, many physical and chemical properties can be tuned for applications.
• Technology is expected to revolutionize industrial activity, medicine, and energy production.
Dept. of Chemistry and Physics
Preparation of ZnS/CdS:• 10 g of sodium polyphosphate was dissolved in 80 mL
of deionized water in 200 mL of beaker• 10 mL of 1.0 M Zn(Ac)2 or Cd(ClO4)2 was added with
stirring• 10 mL of 0.85 M Na2S was also added in one portion• After mixing for 5 minutes, the solution is centrifuged
@ 3500 RPM for 10 minutes• The solution was decanted, the solid was washed and
centrifuged again. 250 mL of water was added to suspend the particles for further experiments
Dept. of Chemistry and Physics
Preparation of MoS2 • 4% surfactant (Dioctyl sulfosuccinate) was dissolved in 50
mL of degassed mixed xylene• With stirring, Mo(CO)6 (4.30x10-4 mol) was added to the
xylene mixture under an argon blanket• The solution was then heated to 70 °C, maintaining argon
bubbling • Elemental sulfur (9.60 x 10-4 mol) was added and the
mixture was heated to reflux and maintained 140 °C for 1 to 1.5 hours under argon
• The xylene was evaporated in the oven.• Residue was dissolved in acetonitrile and the excess
surfactant was extracted 3 times with hexane and was dried in the oven
Dept. of Chemistry and Physics
Nanoparticle Suspensions
Dept. of Chemistry and Physics
ZnS UV-Vis Spectra
0
1
2
3
200 250 300 350 400
Wavelength(nm)
Abs. 295 nm
Dept. of Chemistry and Physics
0
0.2
0.4
250 350 450 550 650
Wavelength(nm)
Abs
.
450 nm
CdS UV-Vis Spectra
Dept. of Chemistry and Physics
MoS2 UV-Vis Spectra
0
1
2
3
320 420 520 620 720 820 920
Wavelength(nm)
Abs.
750 nm
Dept. of Chemistry and Physics
Enp is calculated from the excitonic absorption peak of the nanoparticle, in JEg is calculated from the known bulk semi-conductor band gap, in J
For ZnS = 3.68eV, For CdS = 2.40eVh is Plank’s constantr is the radius of the nanoparticle,in metersme* is the effective mass of the electron, me is the mass of an electron, in kg
For ZnS = 0.25me For CdS = 0.21memh* is the effective mass of the electron, mh is the mass of an electron, in kg
For ZnS = 0.60me For CdS = 0.80mee is the charge on the electron , in C ε is the dielectric constant of material
For ZnS, 8.3 For CdS, 5.6εo vacuum permittivity constant, in C2J2M-1
re
mmrhEE
ohegnp πεε4
8.1118
2
**2
2
−⎥⎥⎦
⎤
⎢⎢⎣
⎡++=
Particle Size Calculation – Brus Equation
Dept. of Chemistry and Physics
Particle Size - ZnS, CdS
re
mmrhEE
ohegnp πεε4
8.1118
2
**2
2
−⎥⎥⎦
⎤
⎢⎢⎣
⎡++=
Bulk Excitation For ZnS = 337.2 nm
For CdS = 517.0 nm
Nano Excitation For ZnS = 295.0 nm
For CdS = 450.0 nm
Nano Radius: For ZnS: r = 1.68 nm
For CdS: r = 0.92 nm
Brus Equation
Dept. of Chemistry and Physics
Actinometry Use standard actinometry procedures to quantify the amount of light
impinging on a sample
Measures amount of light absorbed by a sample system
Relative measurement as compared to a known oxalate actinometer with quantum efficiency of 0.57
Standard method that allows you to compare your data to other researchers data
Dept. of Chemistry and Physics
Actinometry -Procedure
1. 0.5 mM KMnO4 standardized against Na2C2O4 in 10 mL 1M H2SO4 2. Mix 10 mL of 0.01 M oxalic acid & 0.01 M uranyl nitrate in dark3. Measure 1 mL and repeat three times under lamp and in the dark for 1
hour;4. Samples were titrated with standard KMnO4 dropwise until persistent
pink appeared.5. Amount of oxalate consumed is related to number of photons absorbed
by the sample from the equation
Where is the quantum efficiency of the oxalate actinometer, 0.57
Nanoparticle Photocatalysts Interaction with Biological Systems
Investigation #1
Will nanoparticles of CdS, ZnS and MoS2 photochemically degrade DNA?Will degradation be specific or non-specific?How fast will the nanoparticles degrade DNA?
Investigation #2
Will nanoparticles of CdS, ZnS and MoS2 photochemically sterilize bacteria solutions?
Which nanoparticle systems will do this most efficiently with visible light?What time course is needed to effect a sterilization?
Dept. of Chemistry and Physics
Preparing DNA Samples for CdS/ZnS/MoS2 Photodegradation
• 200 µL of CdS or ZnS or 1.0 mg of dried MoS2 (extracted from the previous procedure) was weighed and combined with 500 µL 0.25 mg/mL calf thymus DNA and 1mL of phosphate buffer, pH 7.
• CdS and MoS2 samples were irradiated at 400 nm and above using a long pass filter.
• ZnS was irradiated between 295-350 nm using a band pass filter.• 20 µL samples were removed at various time intervals (0-40 minutes
depending on experiment) and combined with sample loading dye• Samples were analyzed by electrophoresis at 120 V, on 1% agarose in
TAE running buffer• Gels were stained with ethidium bromide and photographed.
Dept. of Chemistry and Physics
DNA PictureHigher MW Top Lower MW BottomTime Course: Left to right increasing timeMoS2: 32 min ZnS: 30 min CdS: 35 min
Dept. of Chemistry and Physics
Plate Count Method for E. coli
Control –1 mL of Escherichia coli (E.coli)
Nano –200 µL Nano particle & 1 mL of E.coli
Bulk –1.3mg Bulk CdS, 1.7 mg Bulk ZnS or 2.0 mg Bulk MoS2 and 1 mL of E.coli
Put one of each in the dark, and one of each under lamp CdS, MoS2 @ > 400 nm for 2 hourZnS @ 295 – 350 nm for 1 hour
Dept. of Chemistry and Physics
Control Dark for CdS:
Total dilutions(TD)=
Dilution Factors(DF)=
Therefore, # of bacteria in sample=(colonies/drop)x(DF)=(8 colonies / drop)x(5.0 X 106)=4.0 X 107 colonies forming unit(CFU)
Preliminary DNA data shows that nanoparticles photodecompose DNA non-selectivelyin less than 180 min
Preliminary data also shows that CdS and MoS2 nanoparticles can help photosterilize bacteria samples with 2 hours of exposure to visible light
Dept. of Chemistry and Physics
Acknowledgements•Dr. Judy Awong-Taylor
•National Science Foundation Division of Undergraduate Education: Nanotechnology in Undergraduate Education Grant DUE/NUE 0303994•National Science Foundation Course Curriculum and Improvement Grant DUE/CCLI - 9952343•USG Matching Grant•AASU College of Arts and Sciences, Department of Chemistry and Physics•AASU Research and Scholarship Grant / Gignilliat Scholarship