A cationic polymer nanobrush was synthesized, attachedto a MALDItarget, and used for the fractionation of peptides and proteins basedon their pI, prior to analysis by MALDI-MS. The cationic polymer nanobrushwas synthesized on a gold substrate by AIBN photoinitiated polymerization,using a 70:30 ratio of 2-aminoethyl methacrylate hydrochloride (AEMA):N-isopropylacrylamide (NIPAAM). This brush showed selectivityfor adsorption of acidic peptides and proteins and allowed fractionationof simple two-component mixtures to be completed in less than 10 min.The brush-adsorbed biomolecules were recovered by treating the nanobrushwith ammonium hydroxide, which effectively collapsed the brush, therebyreleasing the trapped compounds for MALDI MS analysis. These resultsdemonstrate that nanobrush can serve as a convenient platform forrapid fractionation of biomolecules prior to analysis by MALDI-MS. [ABSTRACT FROM AUTHOR]