Selective detection of homocysteine by laser desorption/ionization mass spectrometry

This article describes the use of 2,3-naphthalenedicarboxaldehyde (NDA) as a selective probe for the determination of homocysteine (HCys) via fluorescence measurement and laser desorption/ionization mass spectrometry (LDI-MS). The derivatives of three aminothiols-HCys, glutathione (GSH), and gamma-glutamylcysteine (gamma-Glu-Cys)-with NDA under alkaline conditions possess different fluorescence emission characteristics, which allow us to identify them from amines, amino acids, and thiols. By selecting appropriate pH and excitation wavelengths, the limits of detection (LODs) at a signal-to-noise ratio of 3 were 5.2, 1.4 and 16 nM for HCys, GSH and gamma-Glu-Cys, respectively. Additionally, strong UV absorption of the NDA-HCys derivative was further observed at 331 nm; it could be directly detected by LDI-MS with a 337-nm nitrogen laser. Selective detection of HCys has been achieved by conducting the LDI-MS of the NDA-HCys derivative, which was found at m/z 406.9. The lowest detectable concentration of the NDA-HCys derivative in this approach was 500 nM. Quantitative determination of HCys in urine samples was accomplished by LDI-MS. Also, a calibration curve was created from plasma samples spiked with standard HCys (20-100 microM). The experimental results suggest that our proposed methods have great potential in clinical diagnosis and metabolomics application.