Rapid MALDI mass spectrometric analysis with prestructured membrane filters and functionalized diamond nanocrystals

A solid-phase extraction method based on prestructured membrane filters and functionalized diamond nanocrystals is developed to facilitate analysis of biopolymers with MALDI mass spectrometry. The method integrates isolation, purification, and concentration in one step and is adaptable to high-throughput peptide fingerprint mapping of intact proteins and enzymatic digests. The feasibility of the method was demonstrated using diamond nanocrystals surface-derivatized with carboxylate groups and subsequently coated with poly-lysines. These nanocrystals, which are capable of extracting proteins from highly dilute solutions contaminated with salts and detergents, can be easily isolated by filtration through paraffin-coated PVDF membrane filters pre-patterned with channels for direct MALDI mass spectrometric analysis. This method is facile, easy to operate, and the analysis of each sample solution (with a volume up to 500 μL) can be completed in 10 min. With this method, it is possible to achieve high-throughput analysis of proteins by preparing an array of filtration spots on paraffin-coated PVDF membrane that matches the MALDI sample target of the commercial mass spectrometer.