Question 13

Question 1

q13a)

Magnetic iron oxide nanoparticle clusters (MIONs) represent a versatile platform for diagnosis and therapy. Unfortunately, the surface functionalization of MIONs is difficult. If one could coat MIONs with a gold layer,then it would be possible to attach biomolecules (for better biocompatibility) using thiol chemistry. However, it is also difficult to directly attach gold to iron oxide nanoparticles. Therefore, the MIONs are first coated with a silica layer, then seeded with gold nanoparticles and finally a continuous gold layer is grown (see Figure).
When answering the questions, follow the strategy shown in the figure (the reaction steps a)‐e)) correspond to the questions below. VL 4

How would you synthesize magnetic iron oxide nanoparticles and how would you assemble them into clusters?

Answer 1

Heating up method:
- synthesis of iron-oleate complex (hydrophobic): iron chloride (hydrophil) + sodium oleate in water/ethanol/hexane mixture → heat up → wash in water (2-phase system)
- evaporate hexane to get iron-oleate complex (hydrophobic, solid)
- iron-oleate complex dissolved in octadecene (high boiling temp solvent), heated up
- cooled down and ethanol is added to precipitate the nanocrystals
- separate by centrifugation
- use citric acid as surfactant (to prevent agglomeration) 2 phase system: bc FeCl in water but Fe oleate in hexane wash in water to get rid of NaCl

Assembly into clusters:
- redisperse in water and change pH (high → negative charges) or add salts to screen electrostatic repulsion and cause agglomeration of NP = MIO

Change size of clusters: with amount of salt or pH strength

Question 2

q13b)

How would you do the silica coating?
Briefly discuss the different experimental steps and provide possible chemicals and solvent(s).

Answer 2

• put clusters in water and ethanol
• add TEOs: Tetraethyl orthosilicate
• the hydroxyl groups (-OH and -O- negative charged) that can react with the hydrolyzed TEOS (TEOS hydrolyze with the water) = condensation => silica coating
• wash to remove excess TEOS

Critical thinking:
- hydrolysis and condensation of just TEOs: TEO can hydrolyze and form silica → we only want condensation with the clusters → use ethanol to stabilize TEOs

Question 3

q13c)

How would you attach amino‐groups to the surface? Provide possible chemicals.
What is the role of these amino groups?

Answer 3

Silica coating: -OH groups at the end, hydrophilic

Use amine terminated silane (charge not pH dependant) or Trizma which attach to the silica Role of the amino groups: have a positive charge

Critical thinking: Trizma also pH independent?

Question 4

q13d)

How would you do the gold seeding?

Answer 4

Use gold NP from citrate route which are negatively charged due to the citrate on the surface. Mix in water (both are hydrophilic) => electrostatic attraction between the positive charged MIONs and the negatively charged gold NP

Question 5

q13e)

How would you grow a continuous gold layer?

Answer 5

• Use the already attached gold seeds as nucleation site for the gold layer: add HAuCl and ascorbic acid (step wise to reduce the risk of nucleation of the gold itself as its reduced less fast)
• other possibility: attach enough seeds to be able to sinter them together: problem: uniformity, high temperature