Semiconductor cadmium sulphide nanoparticles as matrices for peptides and as co-matrices for the analysis of large proteins in matrix-assisted laser desorption/ionization reflectron and linear time-of-flight mass spectrometry.

The use of semiconductor cadmium sulphide nanoparticles (CdS NPs) capped with 4-aminothiophenol (ATP) and 11-mercaptoundecanoic acid (MUA) is described for the first time as matrices and as co-matrices for the analysis of peptides and proteins in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). UV-visible spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied for the characterization of functionalized CdS NPs. The synthesized CdS-ATP and CdS-MUA NPs exhibit uniform size distribution with diameter of 15-25 nm and 20-30 nm, respectively. The -NH(2) (ATP) and -COOH (MUA) groups modified on the surfaces of CdS NPs provide ionizable moieties for efficient transfer of protons during the desorption/ionization of analytes. The functionalized CdS NPs have desirable properties for the analysis of peptides in reflectron MALDI-TOF-MS with suppressed background noise and increased mass resolution (4-13-fold) in linear MALDI-TOF-MS. The application of CdS-MUA NPs and SA as the co-matrices in MALDI-MS is demonstrated for the analysis of hydrophobic proteins from soybean.