(179p) Characterization of Commercial Antifoams for Use in Immunoassay Diluents

Immunoassays are a key tool for clinical and research laboratories. Immunoassays are often solution-based kits made up of an active ingredient(s) in a diluent(s) and executed in multi-step automated systems. The diluents of the solutions are formulated to prevent any of the assay components from aggregating or dropping out of solution while ensuring accurate, optimal, and repeatable results. These diluents can include buffers, salts, chelators, proteins, surfactants, and antifoams. Antifoam is used in these 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. Selection of antifoam and antifoam concentration is very assay dependent since the presence of foaming agents varies by the diluent formulation.

In this study, several commercial, polydimethylsiloxane-based antifoams were tested to evaluate their potential for use in immunoassays. Shake testing was performed to determine the minimum antifoam concentration needed to defoam solutions of common diluent formulations. The shake test evaluated how much foam initially forms, how fast foam is eliminated, and how many times foam can be eliminated rapidly. The effect antifoams had on the rheological properties of diluents was evaluated using an oscillatory rheometer. Since the antifoams of interest are hydrophobic in nature, their effect on the air-liquid interface was analyzed using Brewster Angle Microscopy to address their impact on automatic pipetting liquid detection. These three methods assist with the characterization of antifoams for use in immunoassays.