Determination of plasmin in milk using QCM and ELISA methods

Abstract Quartz crystal microbalance (QCM) biosensor for detection plasmin (PLA) in milk using β-casein as a substrate immobilized at piezocrystal surface was reported. The cleavage of β-casein induced by PLA within the concentration range 0.1–40 nM resulted in an increase of series resonant frequency, fs, and a decrease of motional resistance, Rm, due to removal of short peptide fragments from the crystal surface and decrease of viscosity contribution, respectively. The sensor was verified in both raw and spiked milk samples of various origins (cow, goat, sheep). The sensor response has also been studied for trypsin and α-chymotrypsin activities. Sensor technology achieved a limit of PLA detection (LOD) 167.16 ± 39.36 pM at pH 7.4. Similar LOD, 121.98 ± 18.30 pM, was confirmed by Enzyme Linked Immunosorbent Assay (ELISA) test performed in-parallel with the biosensor measurements. Atomic force microscopy (AFM) confirmed cleavage effect of PLA on the surface covered by β-casein.