The 40nm Standard
For most lateral flow assays, 40nm gold is the industry standard. It offers the best balance between color intensity (optical density) and steric stability against aggregation.
When to Use 20nm?
Smaller 20nm particles have a higher surface-area-to-volume ratio, allowing for higher antibody loading density. This can be advantageous for competitive assays where maximizing binding sites is crucial, though the visual signal is less intense (pink vs. red).