Increasing surface capacity for on-probe affinity capture MALDI-MS via gold particle attachment to allyl amine plasma polymers.

In this study, we demonstrate that the protein binding capacity of a surface modified matrix-assisted laser desorption/ionization (MALDI) target can be increased significantly by architecturing the surface of the MALDI probe using gold microparticles. In the present approach, a MALDI target, initially modified via pulsed rf plasma deposition of an allyl amine polymer thin film, is subsequently architectured via reaction with 2-iminothiolane and surface attachment of gold microparticles. The modified probe is then exposed to thiolated biotin to introduce an avidin binding element on the surface of the gold beads. The protein binding capacity of this architectured target is compared with a similarly plasma polymer modified MALDI target that is directly biotinylated. Application of various surface concentrations of avidin to the two probes and MALDI-MS analysis of avidin contained in the solution removed from the probe reveals that saturation of the gold-particle architectured target occurs at a factor of 15-30 higher applied surface concentration, as compared with the unarchitectured target. Furthermore, MALDI-MS analysis of the avidin retained on the two probes reveals that the limit of detection is lowered by a factor of 15-20 on the gold-particle architectured target as compared with the unarchitectured target.