Method for fabricating a gold nanoparticle

1. Method for fabricating a gold nanoparticle, the method comprising the steps of:

contacting a gold ion with a protein, wherein the protein has an inner cavity that can accommodate the gold ion;

separating the protein with the encapsulated gold ion(s) from non-encapsulated gold ions;

contacting the protein-encapsulated gold ion with a first reductant to reduce the gold ion and form a gold nanocluster seed in the inner cavity of the protein by adding the first reductant to a solution comprising the protein-encapsulated gold ion, wherein the first reductant is a strong reductant; and

contacting the gold nanocluster seed in the inner cavity of the protein with a second reductant to mineralize and grow the gold nanoparticle by separately adding the second reductant to the solution after the first reductant is added to the solution, wherein the second reductant is a weak reductant.

2. The method as claimed in claim 1 , wherein the strong reductant is selected from the group consisting of sodium borohydride (NaBH 4 ), diborane (B 2 H 6 ), diisobutylaluminum hydride ((i-Bu 2 AlH) 2 ), lithium triethylborohydride (LiEt 3 BH), potassium borohydride (H 4 BK), diborane (B 2 H 6 ), amineborane, ammonia borane (H 3 NBH 3 ) dimethylamine borane ((CH 3 ) 2 NH:BH 3 ), and a mixture thereof.

3. The method as claimed in claim 1 , wherein the weak reductant is selected from the group consisting of ascorbic acid (C 6 H 8 O 6 ) and a salt thereof, citrate, potassium bitartrate (KC 4 H 5 O 6 ), potassium tartrate (K 2 C 4 H 4 O 6 ), L-cysteine, thioglycerol, sodium tartrate (Na 2 C 4 H 4 O 6 ), oxalic acid (C 2 H 2 O 4 ), sorbic acid (C 6 H 8 O 2 ), fumaric acid (HO 2 CCH═CHCO 2 H), and a mixture thereof.

4. The method as claimed in claim 1 , wherein the protein is selected from the group consisting of Horse Spleen Apoferritin (HAS), ferritin, ferritin-like protein, apoferritin, viral capsid, vault protein, and Dps (DNA-binding proteins from starved cells) protein.

5. The method as claimed in claim 1 , wherein the step of contacting the gold ion with the protein comprises

mixing the protein with an auric acid, wherein the gold ion is derived from the auric acid;

incubating the mixture at room temperature for about 3 hours to allow the gold ion to be transported into the inner cavity of the protein; and

subjecting the incubated mixture to size-exclusion chromatography to desalt the incubated mixture.

6. The method as claimed in claim 5 , wherein the auric acid is chloroauric acid (HAuCl 4 ).

7. The method as claimed in claim 5 , wherein in the mixing step, the mixture of protein cage:auric acid has a molar ratio of about 1:1000.

8. The method as claimed in claim 5 , wherein the size-exclusion chromatography is performed using a desalting column.

9. The method as claimed in claim 1 , wherein in the step of contacting the gold nanocluster seed in the inner cavity of the protein with the second reductant, an auric acid is added.

10. The method as claimed in claim 9 , wherein the auric acid is chloroauric acid (HAuCl 4 ).

11. The method as claimed in claim 1 , wherein the step of contacting the gold nanocluster seed in the inner cavity of the protein with the second reductant is carried out by incubating overnight at room temperature.

12. The method as claimed in claim 11 , wherein the nanoparticle grows until it matches the size of the inner cavity of the protein.