Maltodextrin for Stabilizing CG

[Kephra]

Found this in a paper by Guy E. Abraham:

Preparation of Colloidal Gold: Aqueous dispersion of colloidal gold (Aurasol [R]) was prepared by the author at a concentration of 1,000 mg/L (1,000ppm) using the citrate method of Frens, (4) with several proprietary modifications. Maltodextrins (Food Grade) were used at the concentration of 2.5% to prevent autoaggregation of the small colloid particles. It required 10 years of on and off research to optimize the stability of the colloids in concentrated preparations as high as 5,000 mg/L (5,000ppm) and to maintain particle sizes of the gold colloids with ruby red color below 20 nm consistently. Many batches with blue and violet colors were discarded in the process. Gold colloids of the blue color could not pass through a 100-nm filter and precipitated out of the solution within days of preparation. But gold colloids of the violet color were more stable and could pass through a 100-nm filter, but not a 20-nm filter. They were used in the study of the normal subjects to be described later. However, they were devoid of noticeable effect in the subjects tested.

LINK

[Heino_R]

I've again what's on the shopping list. 

[Kephra]

I've again what's on the shopping list. 

There is a nutritional produce called Carbo Gain here in the USA which claims to be 100% maltodextrin.  Its cheap enough, under $10 for 2 lb.
http://www.iherb.com/Now-Foods-Carbo-Gain-2-lbs-908-g/451?at=0
I've already gone shopping

[kjdyatta]

When I first read this I understood that maltodextrin added to the gold chloride and citrate solution. Was my understanding correct, or does the use of maltodextrin actually replace the use of citrate?

Thanks

[Kephra]

Here's a formula which works for me. 

1.25 ml 1% gold chloride (actual gold weight 12.5 mg)
40 mg Sodium Carbonate Na2CO3  (NOT baking soda, this is washing soda)
125 mg Maltodextrin  (Sold here as Carbo-Gain)
50 ml distilled H2O

Produces 50 ml of 250ppm CG.

I don't know if it will be stable long term, but mine has not changed in a couple of weeks.

[rzero]

5000 ppm? Wow. Even your 250 ppm is very cool Kephra. Is it still holding up? Is this the highest concentration you have gotten? And why the use of carbonate instead of citrate?

[Kephra]

I used to make all my CG with citrate, and it is good for up to 50 ppm or so, but after that it tends to fail.  When I read about Abrams making such high ppm product with maltodextrin, I had to try it.  But maltodextrin is only a reducing agent in an alkaline environment, so I also needed a base.  Thats what the sodium carbonate is for, to raise the ph so that the maltodextrin will work.  It seems to work well, as the first sample I made shows no signs that the gold is falling out.  It looks just like it did the day I made it.

But another base might also work, or it may not need to be basic at all. 

Initially I made twelve 50 ml batches using this process.  I consumed 6 of them so far, and all of the remaining six still look good.

I don't experiment as much with gold as I do with silver because its too expensive to waste so even though this process might be able to be improved, it works well enough that I probably won't try anymore to optimize it.

[qasimta]

Hi Kephra,

I was to repeat this successfully and was very amazed with the speed of reaction. The color was changing instantaneously. The more gold chloride I add the darker the color it gets. Can you please explain the chemistry of this reaction.

Thanks,

[Kephra]

If the reduction of the gold chloride is done by the sodium in the sodium carbonate, then:

I would guess the reaction is:
2HAuCl₄ +3Na₂CO₃ --> 2Au + 6NaCl +2 HCl + 2CO₂ +O₂

If it is done by the maltodextrin, then I can't say because I don't know the formula for maltodextrin.

I think they are both necessary.

The maltodextrin also acts as a stabilizer by adsorbing onto the surface of the gold particles preventing them from aggregating.

[inocentforever]

 Hi kephra last night i was reading some interesting articles in the web, and i find that glycerol could act as a stabilizer to gold nanoparticles, but there was very little info. Do you think the glycerol could work as a stabilizer?

[Kephra]

I personally have not tried glycerine, but if others report that it does, I would assume so. 

[inocentforever]

well.. i manage to get som PVA im excited, because its a problem to get maltodextrine in mexico, and ordering it from iherb  lasta about 5 weeks and they dont waratee the deliver because of the mexican customs so.. im planning to stabilize gold with PVA.

 check this link
http://it.science.cmu.ac.th/ejournal/modules/journal/file/11-01-26-077e2.pdf

my question is... if it is ok to add the pvp after i make the CG ( when it is already red ) and stirr it hard enough so the pva dissolves in the water and capp the gold nanoparticles?

   Thanks

[inocentforever]

 sorry i didnt finish,    i dont use citrate because  the sodium citrate i buy here in my town seems not to work very well.
and i manage to get some eye drops of pure PVA  to be more accurate  14mg per each ml.   How many drops would you use os PVA in a 250 ml batch of colloidal Gold_.

[Kephra]

sorry i didnt finish,    i dont use citrate because  the sodium citrate i buy here in my town seems not to work very well.
and i manage to get some eye drops of pure PVA  to be more accurate  14mg per each ml.   How many drops would you use os PVA in a 250 ml batch of colloidal Gold_.

That would depend on how strong (ppm) your CG is.  The CG made in the paper you referenced is very high ppm, which is the reason they needed PVA as a stabilizer.

[RamanShift]

I use maltodextrin. I've attached an image of a bottle I made on the 8th of December. It looks exactly the same now as it does in the image.