Carbon Nanotubes (2,5-Dihydroxybenzoyl Hydrazine) Derivative as pH Adjustable Enriching Reagent and Matrix for MALDI Analysis of Trace Peptides

Abstract

A functionalized carbon nanotube (CNT), CNT 2,5-dihydroxybenzoyl hydrazine derivative, was synthesized and used as both pH adjustable enriching reagent and matrix in matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS) analysis of trace peptides. The derivative reagent, 2,5-dihydroxybenzoyl hydrazine, introduced phenolic hydroxyl and phenyl groups to the surface of the CNT. The former group can provide adjustable surface charge and a source of protons for chemical ionization, and the latter helps to keep strong ultraviolet absorption for enhancing pulsed laser desorption and ionization. It was found that the functionalized CNT was less twisted in a basic condition (pH 10.5), which afforded an increased surface area to volume ratio for adsorption towards trace peptides. However, functionalized CNT becomes deposited in an acidic condition (pH 5) and can be isolated readily from the sample solutions once the nanoparticles have trapped the target analytes, thus providing a novel and convenient alternative method for quick isolation. Compared with the previously reported method on enriching analytes using the pristine CNT, it is observed that the detection limit for analytes can be greatly improved due to enhancing adsorption capacity of the functionalized CNT. Moreover, peptide mixture at concentration as low as 0.01 pg/microL still can be detected after enrichment mediated by the functionalized CNT, while it is difficult to be detected without enrichment at concentration 0.1 pg/microL using alpha-cyano-4-hydroxycinnamic acid (CHCA) as matrix. Therefore, high efficiency of adsorption and enrichment towards trace peptides can be achieved by adjusting pH value of the functionalized CNT dispersion.