Nitrocellulose has a high capacity for adsorbing protein (2,5,10-12). Initial attraction of a protein molecule to the polymer involves interaction between the dipoles of the nitro groups on the polymer and the carbonyl groups in peptide bonds. Adsorption is further enhanced by the interaction between the nitrocellulose and hydrophobic domains within the protein (11). The immunoglobulin (Ig)G binding capacity of lateral-flow membranes exceeds 100 ^g/cm2. Considering that a typical reagent line is 1 mm wide, there is approx 10 ^g of binding capacity available per cm of line length. Because IgG is normally applied at a rate of 1-2 ^g/cm, the binding capacity of the membrane is 5- to 10-fold greater than needed. The adsorption capacity for bovine serum albumin (BSA), which is commonly used as a carrier for drug conjugates, ranges from 60 to 80 ^g/cm2. These values are based on static adsorption assays where the surface is saturated with the protein (12).
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