Antifoam is used in immunoassay formulations to deter foam formation due to the presence of foaming agents (e.g. surfactants and proteins). Antifoam is added at the minimum effective concentration so foam is eliminated without interfering with the assay. Due to the complex nature of immunoassay formulations, there is a concern that antifoam will not readily mix into an aqueous immunoassay solution and instead will form small pockets with high concentrations of antifoam. One technique to improve dispersion is to predilute the antifoam in a small amount of the final solution and then add the prediluted antifoam to the solution.
The effect of predilution on two commercial, polydimethylsiloxane-based antifoams was studied. The antifoams had initial active concentrations of 3% and 45%. The addition of antifoams at select predilution concentrations to immunoassay solutions was visualized with and without mixing. The bulk rheological properties of the prediluted antifoams were compared with the unprediluted antifoams. The surface tension of the prediluted antifoam was compared with the surface tension of solutions with no antifoam and with antifoam at the final concentrations.