Surface‐modified TiO₂ nanoparticles as affinity probes and as matrices for the rapid analysis of phosphopeptides and proteins in MALDI‐TOF‐MS

Abstract

We utilized three different types of TiO(2) nanoparticles (NPs) namely TiO(2)-dopamine, TiO(2)-CdS and bare TiO(2) NPs as multifunctional nanoprobes for the rapid enrichment of phosphopeptides from tryptic digests of α- and β-casein, milk and egg white using a simplified procedure in MALDI-TOF-MS. Surface-modified TiO(2) NPs serve as effective matrices for the analysis of peptides (gramicidin D, HW6, leucine-enkephalin and methionine-enkephalin) and proteins (cytochrome c and myoglobin) in MALDI-TOF-MS. In the surface-modified TiO(2) NPs-based MALDI mass spectra of these analytes (phosphopetides, peptides and proteins), we found that TiO(2)-dopamine and bare TiO(2) NPs provided an efficient platform for the selective and rapid enrichment of phosphopeptides and TiO(2)-CdS NPs efficiently acted as the matrix for background-free detection of peptides and proteins with improved resolution in MALDI-MS. We found that the upper detectable mass range is 17 000 Da using TiO(2)-CdS NPs as the matrix. The approach is simple and straightforward for the rapid analysis of phosphopeptides, peptides and proteins by MALDI-MS in proteome research.

Nanomaterial-based miniaturized extraction and preconcentration techniques coupled to matrix-assisted laser desorption/ionization mass spectrometry for assaying biomolecules

“…Recently, our group reported various metal-oxide NMs, including SiO 2 [106], ZrO 2 and ZrO 2 -SiO 2 [107], and TiO 2 [108], as affinity and concentrating probes for enhancing peptide and protein signals in MALDI-MS. On the basis of electrostatic interaction, SiO 2 [106], ZrO 2 and ZrO 2 -SiO 2 [107] NPs were used as electrostatic affinity probes for the isolation and concentration of peptides (Leu-enk, Met-enk), thio peptide (thio) and angiotensin I and II (Angio-I and -II) and milk proteins before AP-MALDI-MS analysis. Using these approaches, the signal intensities of peptides (Leu-enk, Met-enk, Angio-I and II, HW6) and proteins (α-casein and β-casein) ions were increased 5-11-fold, with the generation of very clean mass spectra.…”

“…This method proved an option for sample clean-up that allows selective extraction of the desired analytes or selective rejection of interfering species. Similarly, bare TiO 2 , TiO 2 -dopamine and TiO 2 -CdS NM-based SALDI-MS was described for the analysis of peptide (gramicidin D) and proteins (myoglobin, cytochrome c, α-and β-caseins) by MALDI MS [108]. It was demonstrated that the TiO 2 -CdS-NPs served as an efficient matrix for background-free detection of peptides in MALDI-MS. Table 2 shows the potential of NP-based MALDI-MS approaches for bioassays.…”

Semiconductor Nanomaterials-Based Fluorescence Spectroscopic and Matrix-Assisted Laser Desorption/Ionization (MALDI) Mass Spectrometric Approaches to Proteome Analysis

“…Our group also described the enrichment of peptides and proteins using ZrO 2 and ZrO 2 -SiO 2 NPs [117] and bare TiO 2 , TiO 2 -dopamine and TiO 2 -CdS [118] by MALDI-MS. The target analytes were effectively trapped and the concentrated target analytes (Leu-enk, Met-enk, thio peptide (thio) and angiotensin I and II (Angio-I and -II) and milk proteins) from the biocomplex samples through electrostatic [117] and covalent interactions [118] between nanomaterials and target analytes. These approaches provide efficient platforms for sensitive analysis of peptides and proteins (5–11 folds).…”

Effect of polydimethylsiloxane (PDMS) coating on TiO2-based MALDI matrix for dimethyl methylphosphonate (DMMP) analysis

“…However, the relationship between the matrix-analyte interaction and MALDI-MS signal intensity seems to be rather complex, i.e., a stronger interaction between a matrix and an analyte can play either a positive or negative role in the MALDI-MS. In recent years, titanium oxide (TiO 2 ) has been widely used as matrix in the MALDI-MS for detecting phosphopeptide due to the high specific affinity of the surface hydroxyl groups of TiO 2 toward phosphorous, enriching the analytes on matrix surface and thereby enhancing MALDI-MS signals [33][34][35][36]. On the other hand, there are also examples that analyte signals in the MALDI-MS analysis can be decreased with increasing interaction strength between matrix surface and analyte, most likely due to the fact that weekly bound analyte can be more efficiently incorporated into the MALDI matrix [37][38][39][40].…”