1. Characterization of Bare and Surface-Modified Gold Nanoparticles
Department of Chemical and Environmental Engineering
University of California, Riverside
Thi (Kathy) Nguyen Huynh
Graduate student mentor: Hyunjung N. Kim
Advisor: Dr. Sharon Walker

2. Outline Background Objectives Experimental Approach Results
-Bare Gold Nanoparticles (GNPs)
-Surface-modified GNPs
Conclusions to date
Acknowledgements

3. Background Nanostructures are popular for many industrial applications
Ongoing studies investigating the interactions between
nanostructures with living organisms
Nanostructures are source of environmental contamination
By the year of 2025, 48 countries will be short of fresh water  water reuse/recycling will become standard
Therefore, the ability to remove these nanostructures must be determined.

4. Objectives To determine what physical and chemical mechanisms control
◈ Overall project’s objective:
To determine what physical and chemical mechanisms control
the transport and fate of nanostructures in aquatic environments.
Task 1: Synthesis and Characterization of One-Dimensional Nanostructures
Task 2: Radial Stagnation Point Flow (RSPF) experiments
Task 3: Filtration experiments
◈ Specific objectives – initiating task 1:
To establish methods to characterize surfaces of Gold Nanoparticles (GNPs)
To compare characteristics of bare and surface-modified GNPs (S-GNPs)

5. Experimental Approach
◈ Model nanoparticles (GNPs)
- Synthesis done by SUNRISE student in Dr. Myung’s lab
- Diameter: 200 nm
- Length: 2.5 – 4.0 µm
◈ Surface Modification (S-GNPs) S O H
- 3-Mercapto-1-Hexanol (C6H14OS)
- Procedure
Wash with DI water for 7 times: centrifuge at rpm for 2 minutes each time
3hrs
GNPs + 1mM 3-Mercapto-1-Hexanol
(1mL) (2mL)

6. Experimental Approach
◈ Surface Characterization
Size Measurement
(Inverted microscope Olympus IX70)
Hydrophobicity
(VCA Optima Goniometer)
Electrokinetic properties
(ZetaPALS)

7. What is Electrokinetic Property?
A particle’s ability to move in the electromagnetic field
ZetaPALS measures the particles’ mobility, and then calculates to give zeta potentials or the surface charge values
Mechanism:
Point of measurement
Potential
Distance from surface
Stern layer

8. for these particles and in this condition
Results – Electrokinetic Properties of GNPs
◈ Effect of concentration
◈ Effect of size
pH: 5.8, DI water, 3 µm
pH: 5.8, DI water
Optimum concentration
(OD546nm) :
Mobility ≠ f (size)
for these particles and in this condition

9. Results – Electrokinetic Properties of GNPs
◈ Effect of valence and ionic strength
As ionic strength increased in the presence of salt solutions, mobility became less negative (charge on particle approached neutral)
Valance had an important role on mobility: in the presence of divalent cations, mobility was less negative than that in the presence of monovalent cations.
pH: 5.8

10. What is Hydrophobicity?
Hydrophobicity refers to a surface’s property of being water-repellent
Task: To what degree are GNPs hydrophobic?
Contact Angle Method
gLG
Hydrophobic: ө>90o
Hydrophilic: ө<90o
Water droplet ө
gSG
gSL
Solid surface

11. Results – Hydrophobicity of GNPs
◈ Contact angle measurement
- Solution concentration: OD546nm : (2.5x dilution)
Glass
20 μL
70 μL
100 μL
200 μL
Optimum concentration
Contact angle of Bare GNPs :  3.2 O
 Surface of bare GNPs: Hydrophobic

12. Results – Electrokinetic Properties of
Bare GNPs vs. S-GNPs
Why surface-modified?
- The mobility of S-GNPs was less negative than that of bare GNPs in the presence of KCl. However, the difference was not significant in the presence of CaCl2.
- Valence played an important role on GNPs’ mobility regardless of the presence of 3-mercapto-1-hexanol groups.
pH: 5.8

13. Results – Hydrophobicity of
GNPs vs. S-GNPs
Bare GNPs
S-GNPs
Contact angle of S-GNPs :  3.2 O
Surface of S-GNPs: Hydrophobic
Functional groups 3-mercapto-1-hexanol did not affect the hydrophobicity significantly.

14. Proposed Mechanisms
Why did mobility of GNPs decrease in the presence of 3-mercapto-1-hexanol?
SH end, hydrophilic with
greater affinity to GNPs
Modification
OH end, hydrophilic end
Increase in mobility of GNPs
and
Surface becomes more hydrophilic
Decrease in mobility of GNPs
and
Surface becomes more hydrophobic
◈ Proposed Changes:
Increase in concentration of 3-mercapto-1-hexanol
Increase in amount of time suspending the GNPs in the solution
Reduce the length of the GNPs when keeping the same concentration

15. Conclusions to date
1. Methods to characterize the surface of GNPs has been established. Mobility of GNPs was not a function of concentration nor size, over a range investigated in this study.
2. Solution chemistries (Ionic strength and valence) considerably influenced mobility of bare and surface-modified-3-mercapto-1-hexanol GNPs.
3. Mobility of S-GNPs was less negative than that of bare GNPs in the presence of KCl, while the mobility was not sensitive to the presence of 3-mercapto-1-hexanol in the presence of CaCl2.
4. The surface of bare GNPs was determined to be hydrophobic.
5. The modification of 3-mercapto-1-hexanol did not make a significant difference in hydrophobicity.

16. Acknowledgements The Coordinators of BRITE Program
The bacterial adhesion research lab members
Dr. Nosang Myung and Heather Yang

17. Thank you !!
Questions?