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.

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Nanoparticle Size ReferenceNational Science Foundation:

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

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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

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Nanoparticle Suspensions

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ZnS UV-Vis Spectra

0

1

2

3

200 250 300 350 400

Wavelength(nm)

Abs. 295 nm

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0

0.2

0.4

250 350 450 550 650

Wavelength(nm)

Abs

.

450 nm

CdS UV-Vis Spectra

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MoS2 UV-Vis Spectra

0

1

2

3

320 420 520 620 720 820 920

Wavelength(nm)

Abs.

750 nm

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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

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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

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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

( ) ( )

XAfterBefore molesmoles −

=Φ

Φ

Standardization of Potassium Permanganate

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Titration Data

>400 nm

( ) ( )

XAfterBefore molesmoles −

=Φ

hourEinsteinxx

molmol /1093.1;1059.6107.657.0 766

−−−

×=×−×

=

295-350 nm hourEinsteinxx

molmol /1091.4;1009.3107.657.0 666

−−−

×=×−×

=

hourEinsteinxx

molmol /1046.5;1059.3107.657.0 666

−−−

×=×−×

=>450 nm

# Samples Dark ZnS MoS2 CdSKmnO4(mL) mol C2O4 KmnO4(ml) mol C2O4 KmnO4(ml) mol C2O4 KmnO4(ml) mol C2O4

#1 5.4mL 2.5mL 5.2mL 3.0mL#2 5.3mL 2.4mL 5.1mL 2.1mL#3 5.4mL 2.5mL 5.5mL 3.5mLAverage 5.367mL 6.7E-6mol 2.47mL 3.09E-6mol 5.27mL 6.59E-6mol 2.87mL 3.59E-6mol

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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?

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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.

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DNA PictureHigher MW Top Lower MW BottomTime Course: Left to right increasing timeMoS2: 32 min ZnS: 30 min CdS: 35 min

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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

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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)

( ) 75

100.202.0101 −×=×⎟

⎠⎞

⎜⎝⎛ mlml

67 100.5

100.21

×=⎟⎠⎞

⎜⎝⎛

× −

Example Calculation

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Plate Count Data

Samples CdS ZnS MoS2colonies/drop #dilution CFU colonies/d #dilution CFU colonies/d #dilution CFU

Control Dark 8/drop 5th 4.00E+07 17/drop 2nd 8.50E+04 6/drop 3rd 3.50E+05Light 17/drop 4th 8.50E+06 18/drop 2nd 9.00E+04

Bulk Dark 6/drop 5th 3.00E+07 13/drop 2nd 6.50E+04 19/drop 1st 9.50E+03Light 4/drop 3rd 2.00E+05 7/drop 2nd 3.50E+04

Nano Dark 2/drop 5th 1.00E+07 5/drop 3rd 2.50E+05 2/drop 1st 1.00E+03Light 4/drop 3rd 2.00E+05 None None None

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Conclusions

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

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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

Dept. of Chemistry and Physics