Screening Assay of Very Long Chain Fatty Acids in Human Plasma with Multiwalled Carbon Nanotube-Based Surface-Assisted Laser Desorption/Ionization Mass Spectrometry

Peroxisomal disorders are characterized biochemically by elevated levels of very long chain fatty acids (VLCFAs) in serum. Herein, we describe a novel approach for quantification of VLCFAs in serum, namely, eicosanoic acid (C20:0), docosanoic acid (C22:0), tetracosanoic acid (C24:0), and hexacosanoic acid (C26:0). The methodology is based on (i) enrichment of VLCFA derivatives using multiwalled carbon nanotubes (MWCNTs); (ii) quantification using stable isotope-labeled internal standards; and (iii) direct detection using MWCNT-based surface-assisted laser desorption/ionization-time-of-flight mass spectrometry (SALDI-TOFMS). Four kinds of MWCNTs (Aldrich 636843, 636495, 636509, and 636819) of different lengths and diameters were tested using the developed technique. The data show that 636843, the MWCNT with the largest outer diameter (o.d.), the widest wall thickness, and shortest length, had the best limit of detection (0.5-1 mu g/mL) We also found that there was no significant difference in enrichment efficiency of VLCFAs between the four MWCNTs, which suggests that the size of the MWCNT may contribute to desorption/ionization efficiency. To our knowledge, this is the first study to test the enrichment of VLCFAs using MWCNTs of different sizes. We have shown that the VLCFAs adsorbed by MWCNTs can be analyzed by SALDI-TOFMS. In addition, this method does not require liquid/gas chromatography separation, thereby allowing for high-throughput screening of VLCFAs in peroxisomal disorders.