m-PEG-Butyraldehyde (MPEG-bALD) is a linear, monofunctional modified PEG with an aldehyde group at one end and a methoxy group at the other end. The aldehyde can react with hydrazide or aminooxy group for biomolecules Probes and Labels. Hydrophilic PEG chains increase the water solubility of compounds in aqueous media.