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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 (?) Nano-sized delivery systems based on lipids and amphiphilic block copolymers Conjugated Au particles stick to cancer cells A cluster of gold nanoparticles 50 nanometers in diameter created a much larger crater in ice

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.Corti et al, Gold Bulletin 2002, 35/ ) (B.Chaudhuri and S. Raychaudhuri, IVD Technology 2001 March) Nanoswitch Microwire

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 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 Mie interpreted the vivid color of colloidal gold (Verification of Mie theory for light scattering) Turkevich, et. al. studied nucleation and growth of gold particles in sodium citrate (Discussions Faraday Soc. 1951, 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. 1951, 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 H 2 O, 100 O C H 2 AuCl 4 Cit -

8 Reduction by Citrate (Frens,1973) Boil 50mL 0.01% HAuCl 4 (0.29mM) Add 1.75mL 1% Na 3 Citrate 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 r 2 Volume Free Energy r 3 r* G G r r G r * Free energy change for formation of bulk Saturation Ratio: S=C/C s C=concentration; C s =solubility Free energy change for generating the surface: ΔG s =4πr 2 σ=4π(r/a) 2 γ Maximum Gibbs free energy for nucleation γ=surface energy per atomic site

11 Homogeneous Nucleation Size Critical Nucleus Nucleation Rate Activation Energy SmSm

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 1: HAuCl 4 + 3e - = Au 2: Supersaturation build-up 3: Homogeneous Nucleation 4: Growth of Nuclei 5: Stabilization by Dispersants Steps for making Au nanocrystals [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-Fe 2 O 3 ) Prepared by Forced Hydrolysis (Matijević and Schneider, 1978) J. Zhang & J. Buffle, J. Coll Int. Sci 174 (1995) nm pH iep =9.2

17 Preparation of silver particles AgNO 3 + NaBH 4 Na 3 Citrate NaOH Ag Reducing agent Stabilizing agent pH Control

18 Colloidal Stability in Electrolyte Solutions

19 Mechanism of surface Charge Generation 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) OH O-O- COO - X-X- X-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 Electrostatic Repulsion Energy Maximum s R S m = 3 nm for hematite

22 Total interaction free energy V T =V A +V R +V S V S = steric repulsion

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

24 Size Evolution vs. Ionic Strength Fe 2 O 3 : 10mg/L (2.4x10 13 /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 19 th century) (a) The CCC for similar electrolyte solutions is similar but not identical. (b) It is the valency of the counter ion that is of paramount importance in determining the coagulation concentration. According to DLVO theory: CCC~1/z 6

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

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 H2OH2O H2OH2O

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=1.36x10 6 ) Polymer Concentration (ppm) Collision efficiency factorZeta-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

39 Instructor: Dr. Zhen Guo MatE 297, Spring 2006 Bonding Type IV – Van De Walls Force from permanent and induced Dipole

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