New immobilization chemistry for probe affinity mass spectrometry

Probe affinity mass spectrometry (PAMS) is a technique that combines affinity separations directly with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). In this approach, a binding molecule, such as an antibody, lectin or receptor, is covalently attached to the surface of a MALDI probe. This permits the analyte of interest to be selectively captured and concentrated on the probe surface prior to MALDI-MS analysis. A major limitation of our initial PAMS immobilization chemistry was that it produced only a relatively small number of binding sites on the probe, as it was based on forming a single monolayer of the binding molecule. Because of this limitation, we have investigated new immobilization chemistries for PAMS that are not confined by monolayer formation and thus allow a larger number of analyte molecules to be captured by the probe. We have developed a new PAMS chemistry that first attaches very high molecular weight (similar to 500 000) dextrans to the MALDI probe, followed by immobilization of the binding molecules to the probe-bound dextrans. Because the size of each dextran molecule is significantly larger than the binding molecule, multiple binding molecules can be linked to the same dextran chain. We have demonstrated that these surfaces possess approximately 500 times more analyte binding sites than probes prepared with our original PAMS chemistry. This chemistry is applicable to any binding molecule that coantains a primary amine and is suitable, therefore, for a wide range of applications.