Design of buffer exchange surfaces and sensor chips for biosensor chip mass spectrometry

The feasibility of buffer exchange in biosensor chip mass spectrometry, along with the construction of base sensor chips and use of alternative chip chemistries, is demonstrated in this work. Beta-2-microglobulin (β₂m) was used as an analyte and captured in the first flow cell (FC1) on the sensor chip surface by an immobilized anti-β₂m antibody. Low pH buffer was then used to elute the captured analyte from the flow cell and route it to a second flow cell (FC2) downstream that served as a cation exchanger that retains the analyte. Following additional washes in FC1, the analyte present in FC2 was either eluted with a higher pH buffer (to demonstrate the possibility of elution into a downstream trypsin flow cell), or it was subjected to matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry analysis to verify its presence in FC2. In a separate experiment, a gold-sputtered glass slide (base chip) was activated through a formation of 11-mercaptoundecanoic acid self-assembled monolayer and via reaction with 1,1″-carbonyldiimidazole. The activated chip was placed manually into the biosensor and two surfaces (flow cells) were derivatized with antibodies to β₂m and cystatin C (cysC). To evaluate the chip performance, diluted human urine aliquot was injected over the flow cells. Following the surface plasmon resonance analysis, the chip was MALDI-TOF MS analyzed, yielding signals from β₂m and cysC from their respective flow cells. Artifacts arising from the surface chemistries were not observed in the analysis.