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Nanoparticles for Biomedical Applications Part I: Preparation & Stabilization Jingwu Zhang 5/3/06.

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Presentation on theme: "Nanoparticles for Biomedical Applications Part I: Preparation & Stabilization Jingwu Zhang 5/3/06."— Presentation transcript:

1 Nanoparticles for Biomedical Applications Part I: Preparation & Stabilization
Jingwu Zhang 5/3/06

2 Nanoparticles for biomedical applications
Imaging agents Gold, Silver, Quantum Dots, Magnetic Nanoparticles Chemical sensors DNA Modified Au particles Drug delivery devices Nanocapsules Therapeutic agents (?) Conjugated Au particles stick to cancer cells A cluster of gold nanoparticles 50 nanometers in diameter created a much larger crater in ice Nano-sized delivery systems based on lipids and amphiphilic block copolymers

3 Outline Preparation of monodisperse nanoparticles
Gold nanoparticles Methods for achieving uniform particle size Colloidal Stability in electrolyte solutions Surface charge DLVO theory Schulze-Hardy rule Stabilization of Nanoparticles by polymers Polymer adsorption Stabilization mechanisms

4 Preparation of Monodisperse Nanoparticles

5 Possible Applications of Colloidal Gold (C. W
Possible Applications of Colloidal Gold (C.W.Corti et al, Gold Bulletin 2002, 35/ ) (B.Chaudhuri and S. Raychaudhuri, IVD Technology 2001 March)                                               Microwire Nanoswitch

6 Making Colloidal Gold:
1857 Faraday prepared gold colloids by reduction of gold chloride with phosphorus. "Experimental relations of gold (and other metals) to light." In: Philosophical Transactions, 147, Part I, pp , [1]. London Taylor & Francis 1857. 1861 Thomas Graham coined the word “colloid” to describe systems which exhibited slow rates of diffusion through a porous membrane. Zsigmody (Nobel Prize, 1925) developed “seed” method to produce uniform and stable gold sols. 1908 Mie interpreted the vivid color of colloidal gold (Verification of Mie theory for light scattering). 1951 Turkevich, et. al. studied nucleation and growth of gold particles in sodium citrate (Discussions Faraday Soc , No ) 1973 Frens developed a simple sodium citrate reduction method to produce colloidal gold of uniform and controlled size. Ref: M.A. Hayat “ Colloidal Gold” Vol 1, 1989

7 Colloidal Gold Synthesis (Turkevich, et. al. Discussions Faraday Soc
Colloidal Gold Synthesis (Turkevich, et. al. Discussions Faraday Soc , No ) Solution color varies extensively with particle size Usually a deep red, but also dark brown/purple to light orange/yellow Colloid size can be controlled by Au:Citrate ratios Anywhere between 1nm - 100nm Extremely stable Cit- H2AuCl4 H2O, 100OC

8 Reduction by Citrate (Frens,1973)
Boil 50mL 0.01% HAuCl4 (0.29mM) Add 1.75mL 1% Na3Citrate Keep boiling for a few minutes Mean particle size is 12nm (CV 20%)

9 TEM images gold nanoparticles Produced by citrate reduction

10 Homegeneous Nucleation
Interface Energy r2 Volume Free Energy r3 r* DG DGr r DGr* Free energy change for formation of bulk Saturation Ratio: S=C/Cs C=concentration; Cs=solubility Free energy change for generating the surface: ΔGs=4πr2σ=4π(r/a)2γ γ=surface energy per atomic site Maximum Gibbs free energy for nucleation

11 Homogeneous Nucleation
Size Critical Nucleus Nucleation Rate Activation Energy Sm

12 Preparation of Uniform Particles Strategy 1: Control of nucleation
Monodisperse nanoparticles can be produced by confining the formation of nuclei to a very short period, so that the particle number remains constant and all grow together to the same size. This strategy was first used by La Mer to produce highly monodisperse sulfer sols.

13 Steps for making Au nanocrystals
1: HAuCl4 + 3e- = Au 2: Supersaturation build-up 3: Homogeneous Nucleation 4: Growth of Nuclei 5: Stabilization by Dispersants [Au] Metastable Zone: S=1 to Sm

14 Preparation of Uniform Particles Strategy 2: Seeded Growth
Preparation of seed crystals Growth on seeds in meta-stable zone Growth 2:1 3:2 Diameter ratio growth 4:3 The particle size distribution becomes narrower with time. This strategy was first used by Zsigmondy to produce monodisperse gold sols

15 Preparation of Uniform Particles Strategy 3: Aggregation of Nanosized Precursors
This strategy has been employed by Matijevic and co-workers to make a variety of transition metal oxide by controlled hydrolysis techniques

16 Hematite (α-Fe2O3) Prepared by Forced Hydrolysis (Matijević and Schneider, 1978)
pHiep=9.2 50nm J. Zhang & J. Buffle, J. Coll Int. Sci 174 (1995)

17 Preparation of silver particles
Stabilizing agent AgNO3 + NaBH4 Na3Citrate NaOH Ag Reducing agent pH Control

18 Colloidal Stability in Electrolyte Solutions

19 Mechanism of surface Charge Generation
OH O- COO- Ionization of functional groups at surface Ion adsorption from solution Crystal lattice defects (clay mineral system, due to isomorphous replacement of one ionic species by another of lower charge) X- X- X- Si(IV) Al(III)- Al(III)

20 Electrical double layer
Helmholtz Model Guouy-Chapman Model Stern Model

21 Colloidal Stability: DLVO Theory Derjaguin-Landau (1941) & Verwey-Overbeek(1948)
Van der Waals Attraction R s Electrostatic Repulsion Energy Maximum Sm = 3 nm for hematite

22 Total interaction free energy
VT=VA+VR+VS VS = steric repulsion

23 Influence of electrolyte concentration on particle-particle interaction energy
Debye Parameter К ~ I1/2 ~ electrolyte concentration Double layer thickness (unit: Å): К-1 = 3.04/I1/2

24 Size Evolution vs. Ionic Strength Fe2O3: 10mg/L (2. 4x1013/L), pH=3
Size Evolution vs. Ionic Strength Fe2O3: 10mg/L (2.4x1013/L), pH=3.0, 25.0±0.3°C Critical coagulation concentration (CCC): The concentration of an electrolyte about which aggregation occurs rapidly

25 CCC for selected sols

26 Schulze-Hardy rule (recognized at end of 19th century)
The CCC for similar electrolyte solutions is similar but not identical. It is the valency of the counter ion that is of paramount importance in determining the coagulation concentration. According to DLVO theory: CCC~1/z6

27 Stabilization of Nanoparticles by Polymers

28 Colloidal stabilization by polymers

29 Examples of polymers Synthetic polymers
Biopolymers: protein, DNA, Polysaccharide

30 Isotherm of polymer adsorption
Configuration of polymer chain on surface (a) A typical high-affinity polymer adsorption isotherm (b) Langmuir adsorption isotherm, usually followed by small molecules

31 Mechanisms of Colloid stabilization by polymers
Increase in electrostatic repulsion Decrease in attraction energy Decrease in Hamaker Constant Steric repulsion Volume restriction Osmotic effect H2O

32 Destabilization of Colloids by Polymers
Polymer bridging Charge Neutralization Electrostatic Patch Model

33 Double roles of polymers Flocculation and Stabilization
Steric stabilization Charge reversal Electrostatic & steric Increasing polymer concentration

34 Aggregation of Hematite by PAA (Mw=1.36x106)
Polymer Concentration (ppm) Collision efficiency factor Zeta-potential DLA Pre-DLA Post-DLA

35 Effect of Molecular Weight
Collision efficiency factor Zeta-potential

36 Q&A

37 Methods for determining particle size

38 Dynamic Light Scattering (PCS)
                       PM With this method each size measurement takes less than a minute. Thus it is especially useful for aggregation kinetics studies.

39 Bonding Type IV – Van De Walls Force from permanent and induced Dipole

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