Presentation on theme: "Characterization of Bare and Surface-Modified Gold Nanoparticles"— Presentation transcript:
1Characterization of Bare and Surface-Modified Gold Nanoparticles Department of Chemical and Environmental EngineeringUniversity of California, RiversideThi (Kathy) Nguyen HuynhGraduate student mentor: Hyunjung N. KimAdvisor: Dr. Sharon Walker
3Background Nanostructures are popular for many industrial applications Ongoing studies investigating the interactions betweennanostructures with living organismsNanostructures are source of environmental contaminationBy the year of 2025, 48 countries will be short of fresh water water reuse/recycling will become standardTherefore, the ability to remove these nanostructures must be determined.
4Objectives To determine what physical and chemical mechanisms control ◈ Overall project’s objective:To determine what physical and chemical mechanisms controlthe transport and fate of nanostructures in aquatic environments.Task 1: Synthesis and Characterization of One-Dimensional NanostructuresTask 2: Radial Stagnation Point Flow (RSPF) experimentsTask 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)
5Experimental 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)SOH- 3-Mercapto-1-Hexanol (C6H14OS)- ProcedureWash with DI water for 7 times: centrifuge at rpm for 2 minutes each time3hrsGNPs + 1mM 3-Mercapto-1-Hexanol(1mL) (2mL)
7What is Electrokinetic Property? A particle’s ability to move in the electromagnetic fieldZetaPALS measures the particles’ mobility, and then calculates to give zeta potentials or the surface charge valuesMechanism:Point of measurementPotentialDistance from surfaceStern layer
8for these particles and in this condition Results – Electrokinetic Properties of GNPs◈ Effect of concentration◈ Effect of sizepH: 5.8, DI water, 3 µmpH: 5.8, DI waterOptimum concentration(OD546nm) :Mobility ≠ f (size)for these particles and in this condition
9Results – Electrokinetic Properties of GNPs ◈ Effect of valence and ionic strengthAs 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
10What is Hydrophobicity? Hydrophobicity refers to a surface’s property of being water-repellentTask: To what degree are GNPs hydrophobic?Contact Angle MethodgLGHydrophobic: ө>90oHydrophilic: ө<90oWater dropletөgSGgSLSolid surface
11Results – Hydrophobicity of GNPs ◈ Contact angle measurement- Solution concentration: OD546nm : (2.5x dilution)Glass20 μL70 μL100 μL200 μLOptimum concentrationContact angle of Bare GNPs : 3.2 O Surface of bare GNPs: Hydrophobic
12Results – Electrokinetic Properties of Bare GNPs vs. S-GNPsWhy 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
13Results – Hydrophobicity of GNPs vs. S-GNPsBare GNPsS-GNPsContact angle of S-GNPs : 3.2 OSurface of S-GNPs: HydrophobicFunctional groups 3-mercapto-1-hexanol did not affect the hydrophobicity significantly.
14Proposed MechanismsWhy did mobility of GNPs decrease in the presence of 3-mercapto-1-hexanol?SH end, hydrophilic withgreater affinity to GNPsModificationOH end, hydrophilic endIncrease in mobility of GNPsandSurface becomes more hydrophilicDecrease in mobility of GNPsandSurface becomes more hydrophobic◈ Proposed Changes:Increase in concentration of 3-mercapto-1-hexanolIncrease in amount of time suspending the GNPs in the solutionReduce the length of the GNPs when keeping the same concentration
15Conclusions to date1. 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.
16Acknowledgements The Coordinators of BRITE Program The bacterial adhesion research lab membersDr. Nosang Myung and Heather Yang