Identification of Human Plasma Proteins by Trypsin Immobilized Digestion Chip and Electrospray Ionization Tandem Mass Spectrometry
Self-assembled monolayers (SAMs) on coinage metal provide versatile modeling systems for studies of interfacial electron transfer, biological interactions, molecular recognition and other interfacial phenomena. Recently the bonding of enzyme to SAMs of alkanethiols onto Au electrode surfaces was exploited to produce a bio-sensing system. In this work, the attachment of trypsin to a SAMs surface of 11-mercaptoundecanoic acid was achieved using water soluble N-ethyl-N'-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide as coupling agent. Experimental results have revealed that the XPS C1s core levels at 286.3 and 286.5 eV (C with N), 288.1 eV (Amide bond) and 289.3 eV (Carboxylic acid) illustrate the immobilization of trypsin. These data are also in good agreement with FTIR-ATR spectra for the peaks valued at 1659.4 cm-1 (Amide I) and 1546.6 cm-1 (Amide II). Using nano-HPLC-ESI-MS/MS observations, analytical results have demonstrated the human plasma proteins digestion of the immobilized trypsin on the functionalized SAMs surface. For such surfaces, human plasma proteins were digested, which shows the enzyme digestion ability of the immobilized trypsin. The terminal groups of the SAMs structure can be further functionalized with biomolecules or antibodies to develop surface-base diagnostics, biosensors, or biomaterials.