What is the difference between bicarbonate and PBS as a coating buffer in ELISA assay?

PBS and bicarbonate buffer, which are two of the most commonly used coating buffers for ELISAs, differ in their pH—while PBS has a pH of 7.4, bicarbonate buffer has a pH of 9.5. For many antigens, the higher pH of a bicarbonate buffer assists in hydrophobic reactions between amino acids side chains and the polystyrene surface of the plate, thus helping in the coating process.