I used to synthesize Au NPs I think that is useable for high concentration synthesis.

you just need to increase the concentration of HAuCl4 in the solution "briefly; 90 µL of 0.23 M HAuCl4 aqueous solution and 8 mg SDS were added into 20 mL of deionized water and stirred for ~30 min. A 200 µL of freshly prepared 0.1 M NaBH4 was added to this solution and stirred for ~30 min, then, the resulted wine‑red suspension solution was stored at 4 °C"

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Dear Hassan Arkaban, Usually the higher the concentration of HAuCl4 during the synthesis the larger average particle size. I would suggest to use higher concentration of stabilizing agent. I did previously prepared AuNPs suspension up to 4 mM/L 787 mg/L

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