Quantum dot enhancement of peptide detection by matrix-assisted laser desorption/ionization mass spectrometry.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) is a rapid and sensitive tool for characterizing a wide variety of biomolecules. However, invisible "sweet spots" that form during heterogeneous cocrystallization minimize the analytical throughput and affect the reproducibility of MALDI analysis. In this study, visible "sweet spots" were generated on a metallic sample plate by quantum dots (QDs)-assisted MALDI analysis. To the best of our knowledge, this is the first report to demonstrate that "sweet spots" can be observed directly without using a microscope. The proper proportion of matrix to QDs that results in optimal crystallization was also examined. The signals of standard peptides and phosphopeptides obtained by QD-assisted MALDI analysis were 5- and 3-fold higher, respectively, than those obtained by conventional MALDI analysis. For peptide mixtures, the QD-assisted MALDI analysis not only resulted in more intense peptide signals but also resulted in a greater number of peaks, thereby allowing for better detection of individual peptides in peptide mixtures. Moreover, we demonstrated that application of QDs to a radiate microstructure chip followed by MALDI analysis enhanced the detection of peptide signals. Overall, we show that this method is a simple, sensitive, and high-throughput technique for peptide detection.