Carbon nanotubes as affinity probes for peptides and proteins in MALDI MS analysis

Recently, carbon nanotubes (CNTs) have been reported to be an effective MALDI matrix for small molecules (Anal. Chem. 2003, 75, 6191). In a somewhat related study, we have employed CNTs produced by using NaH-treated anodic aluminum oxide (Na@AAO) as a reactive template as the assisting matrix for MALDI analysis upon the addition of high concentrations of citrate buffer. Our results indicate that the mass range can be extended to ca. 12,000 Da and that alkali metal adducts of analytes are effectively reduced. Furthermore, we have employed citric acid-treated CNTs as affinity probes to selectively concentrate traces of analytes from aqueous solutions. High concentrations of salts and surfactants in the sample solutions are also tolerated. This approach is very suitable for the MALDI analysis of small proteins, peptides, and protein enzymatic digest products.