No abstract

A self-assembled-monolayer-modified silicon substrate was successfully used to enhance the sensitivity of peptide detection for atmospheric pressure-matrix-assisted laser desorption/ionization mass spectrometry (AP-MALDI/MS). The effect of surface modification of silicon wafer samples with NH(2) and OH functional groups was investigated. In addition, solvent effects for the preparation of modified NH(2)-functionalized surfaces were examined. The sensitivities for the two peptides were significantly improved, increasing between 12 and 160 times, for bradykinin and gramicidin, respectively, on an NH(2)-modified silicon surface prepared in toluene, over that on a conventional gold substrate. The limits of detection (LODs) for bradykinin and gramicidin using the conventional gold substrate in AP-MALDI/MS experiments were > 0.011 microM and 110 microM, respectively. Using our SAM approach, the LODs for bradykinin and gramicidin in AP-MALDI/MS can be improved to 0.93 nM and 0.33 microM, respectively. This SAM approach for AP-MALDI/MS is simple and sensitive, and can be used for high-throughput analysis.

A novel one-step top-down method is developed for the efficient synthesis of nitrogen-doped carbon nanodots (NCNDs) by using calcination treatment of waste chicken eggshell as resources. Based on the usage of urea as a dopant, the as-synthesized NCNDs are referred to as NCND 1 (no dopant) and NCND 2. The structural and composition analysis indicate that NCND 2 possesses a mean particle diameter of 2.6 nm and an amorphous carbon structure with a lattice spacing of 0.38 nm. Despite having a low Ncontent ($4%), the as-prepared NCND 1 was also found to exhibit excellent photoluminescent properties, low cytotoxicity and could be effectively used for bioimaging, in conjunction with NCND 2.The multi-functional capability of NCND 2 is further demonstrated for stamping, printing, and forensic applications. This work may pave the way for employing carbonaceous waste materials as potential precursors in the synthesis of carbon nanomaterials for wide technological applications.

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.

A novel label-free fluorescence 'turn-on' nanosensor has been developed for highly selective and sensitive detection of phosphorylated species (Ps) in biological samples and living cells. The design strategy relies on the use of Ti(4+)-immobilized polydopamine (PDA) coated reduced graphene oxide (rGO@PDA-Ti(4+)) that serves as an attractive platform to bind riboflavin 5'-monophosphate molecules (FMNs) through ion-pair interactions between phosphate groups and Ti(4+). The as-prepared rGO@PDA-Ti(4+)-FMNs (nanosensor), fluoresce only weakly due to the ineffective Förster resonance energy transfer between the FMNs and rGO@PDA-Ti(4+). The experimental findings revealed that the microwave-assisted interaction of the nanosensor with α-, β-casein, ovalbumin, human serum, non-fat milk, egg white, and living cells (all containing Ps) releases FMNs (due to the high formation constant between phosphate groups and Ti(4+)), leading to an excellent fluorescence 'turn-on' response. The fluorescence spectroscopy, confocal microscopy, and MALDI-TOF MS spectrometry were used to detect Ps both qualitatively and quantitatively. Under the optimized conditions, the nanosensor showed a detection limit of ca. 118.5, 28.9, and 54.8 nM for the tryptic digests of α-, β-casein and ovalbumin, respectively. Furthermore, the standard addition method was used as a bench-mark proof for phosphopeptide quantification in egg white samples. We postulate that the present quantitative assay for Ps holds tremendous potential and may pave the way to disease diagnostics in the near future.