I am trying to AuNP(12nm, in citrate buffer) aggregation with CTAB.

but there is no color change.

here is the condition that I did the experiment

1. AuNP : 12nm, in citrate buffer, 14nM, 10uL

2. CTAB: 100pM~ 100uM (point: 10 order), in 20mM HEPES buffer 7.4pH, 40uL

3. incubation time: 5min~ 30min

why is not changed the color? what factor make the effect on color change?

Please help me!

thank you for your time:)