Signal Enhancement Effect Of Noble Metal—Porous Silicon Chip For MALDI—TOF—MS Deteection And

Low molecular weight peptides (LMWPs) in serum are potential biomarkers for the diagnosis of diseases. The identification of peptide biomarkers in human serum has become an area of high interest in medical research. However, the direct analysis of peptides in serum samples using mass spectrometry is challenging and it is difficult to obtain high quality peptide fingerprint profile due to the low concentration of LMWPs and the significant signal suppression caused by the high concentration of high molecular weight proteins (HMWPs). Therefore, the methods for improving laser desorption/ionization efficiency of analytes in matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) and excluding the interference of HMWPs are urgently needed. Porous silicon (PSi) has high surface area and can effectively enrich the LMWPs in serum sample due to its size exclusion effect. When the PSi is combined with the noble metal nanoparticles, the new metal-semiconductor hybrid structure has the localized surface plasmon resonance (LSPR) effect and the charge transfer capability has been improved. Both of these characteristics are benefit to the ionization process in MALDI detection. In this thesis, the ionization efficiency of MALDI based on the special properties of noble metal-PSi semiconductor material has been explored and its application in serum LMWPs analysis has also been studied.(1) It is summarized the significance of the peptidomics research, and the application of bio-mass spectrometry in peptidomics research. The mesoporous materials’ application in peptide enrichment and the influence factors of ionization efficiency in MALDI have also been introduced. In addition, the photoelectric properties and applications of the noble metal nanoparticles-semiconductor hybrid material are also reviewed.(2) This thesis reports a novel sample plate of MALDI, which is obtained by integration of porous silicon with Au nanoparticles. The new chip combines the size exclusion effect and semiconductor property of the PSi with the special physical and chemical properties of noble metal nanoparticles. The enhancement effect of signal intensity by this chip is proved with insulin as the model sample. To confirm whether the hybrid nanostructure can selectively capture the small peptides and exclude the HMWPs, a model sample consisting of horseradish peroxidase digest and an excess of bovine serum albumin has been tested. Besides, its application to capture low molecular weight peptides from serum sample of colorectal cancer patients and normal subjects in clinical testing are studied. The results show that the new plate could be used for the direct detection of serum sample and obtaining serum peptide fingerprints with high fidelity, and successful discrimination of colorectal cancer patients based on peptide fingerprints is demonstrated. Its accuracy is as high as80%and the chip shows potential application in peptidomics research.(3) The palladium nanoparticles (PdNPs) modified porous silicon (Pd-PSi) chip has been prepared, and its improvement of serum peptides detection has been explored. The mechanisms of MALDI enhancement in this chip have also been studied. With the help of size exclusion effect of PSi, the interference of HMWPs can be efficiently reduced and small molecules in serum would be enriched, leading to higher detection sensitivity of peptides in the low molecular weight region. Besides, the rough surface of PSi is benefit to form uniform crystallization, which can improve the repeatability of the MALDI detection. Due to the localized surface plasmon resonance (LSPR) effect of palladium nanoparticles, the Pd-PSi chip also has a plasmon resonance in the UV region and can improve the laser energy absorption capability, which contributes to the desorption of analytes. The charge transfer property between palladium nanoparticles and porous silicon semiconductor would help the accumulation of positive charge on the surface of the palladium nanoparticles, which can also promote the desorption and ionization process of small analytes under positive liner detection mode.