Quantum dots laser desorption/ionization MS: multifunctional CdSe quantum dots as the matrix, concentrating probes and acceleration for microwave enzymatic digestion for peptide analysis and high resolution detection of proteins in a linear MALDI-TOF MS

We report the first use of fanctionalized cadmium selinide quantum dots (CdSe QDs) with 11-mercaptoundecanoic acid (MUA) as the matrix for the selective ionization of proteins with high resolution and rapid analysis of amino acids and peptides by using quantum dots laser desorption/ionization mass spectrometry (QDLDI-MS). The mercaptocarboxylic groups of CdSe QDs have been known to be an effective affinity probe to interact with the biomolecules at low abundance level. Using these QDs as the matrix, sensitivity of the method was greatly enhanced and the LOQ of peptides was found to be 100 pM with RSD <10%. The QDLDI-MS is capable for the selective ionization of insulin, lysozyme and myoglobin with high resolution, which is not observed with sinapic acid (SA) as the matrix. The QDLDI-MS technique offers many advantages for the analysis of amino acids, peptides and proteins with regard to simplicity, rapidity, sensitivity and the mass spectra were generated in the presence of signal suppressors such as urea and Trition X-100. In addition, the CdSe QDs have been successfully applied as preconcentrating probes for the analysis of digested peptides in lysozyme from chicken egg white by microwave-assisted enzymatic digestion. This indicates that the QDs are able to absorb radiation from microwave and their ability to trap peptides from microwave-digested lysozyme. These results demonstrate that the CdSe QDs are promising candidates for the selective ionization of the analytes with an accurate platform to the rapid screening of biomolecules.