[2][3] Notably, the formulation of Aurodye changed between 1987 and 1990 such that it became incompatible with protein assays,[4] however vendors such as Bio-Rad[5] & Diversified Biotech[4] starting offering colloidal gold formulations that were suitable for protein assays.
These products have since been discontinued and there are no vendors that currently explicitly sell colloidal gold for the assay, however detailed synthetic procedures were published to produce the ~17-40 nm gold nanoparticles that are suitable for the assay, along with modifications to increase the shelf stability of the colloidal gold & adapt the assay to microplate format & increase its sensitivity.
[6] Gold nanoparticles in the ~17-40 nm size range that are presumably compatible with the assay are currently commercially available.
[7] The total protein concentration is readout by an increase in absorbance at 565 nm, which can then be measured using colorimetric techniques, including using microplate readers.
[1] An optimized formulation for the assay to maximize sensitivity in microplate format was described.