Kwan-Ming Ng

Ion Desorption Efficiency and Internal Energy Transfer in Carbon-Based Surface-Assisted Laser Desorption/Ionization Mass Spectrometry: Desorption Mechanism(s) and the Design of SALDI Substrates

Ion desorption efficiency and internal energy transfer were probed and correlated in carbon-based surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using benzylpyridinium (BP) salt as the thermometer chemical. In a SALDI-MS experiment with a N(2) laser (at 337 nm) used as the excitation light source and with multiwalled carbon nanotubes (CNT), buckminsterfullerene (C(60)), nanoporous graphitic carbon (PGC), non-porous graphite particles (G), highly oriented pyrolytic graphite (HOPG), or nanodiamonds (ND) as the SALDI substrate, both the desorption efficiency in terms of ion intensity of BP and the extent of internal energy transfer to the ions are dependent on the type and size of the carbon substrates. The desorption efficiency (CNT approximately C(60) > PGC > G > HOPG > ND) in general exhibits an opposite trend to the extent of internal energy transfer (CNT < C(60) approximately PGC < G approximately HOPG < ND), suggesting that increasing the extent of internal energy transfer in the SALDI process may not enhance the ion desorption efficiency. This phenomenon cannot be explained by a thermal desorption mechanism, and a non-thermal desorption mechanism is proposed to be involved in the SALDI process. The morphological change of the substrates after the laser irradiation and the high initial velocities of BP ions (1100-1400 ms(-1)) desorbed from the various carbon substrates suggest that phase transition/destruction of substrates is involved in the desorption process. Weaker bonding/interaction and/or a lower melting point of the carbon substrates favor the phase transition/destruction of the SALDI substrates upon laser irradiation, consequently affecting the ion desorption efficiency.

Cyclometalated Platinum(II) Complexes as Highly Sensitive Luminescent Switch‐On Probes for Practical Application in Protein Staining and Cell Imaging

Protein-staining platinum: The luminescent switch-on characteristic of the platinum(II) complex can be utilized for staining a series of proteins in sodium dodecyl sulfate-polyarcylamide gels, to give emissive gel images directly under UV light (see figure). The detection sensitivity for BSA protein is down to 6.0 ng, revealing potential practical applications of luminescent platinum(II) complexes in the luminescent signaling of biomolecules.

Gold Nanoparticles and Imaging Mass Spectrometry: Double Imaging of Latent Fingerprints

Latent fingerprint (LFP) detection is a top-priority task in forensic science. It is a simple and effective means for the identification of individuals. Development of nanomaterials which maximize the surface interaction with endogenous substances on the ridges to enhance the contrast of the fingerprints is an important application of nanotechnology in LFP detection. However, most developments in this area have mainly focused on the visualization of the physical pattern of the fingerprints and failed to explore the molecular information embedded in LFPs. Here, we have integrated certain distinctive properties of gold nanoparticles (AuNPs) with imaging mass spectrometry for both the visualization and molecular imaging of LFPs. Two contrasting colors (blue and pink), arising from different surface plasmon resonance (SPR) bands of the AuNPs, reveal the optical images of LFPs. The laser desorption/ionization property of the AuNPs allows the direct analysis of endogenous and exogenous compounds embedded in LFPs and imaging their distributions without disturbing the fingerprint patterns. The simultaneous visualization of LFP and the recording of its molecular images not only provide evidence on individual identity but also resolve overlapping fingerprints and detect hazardous substances.

A High-Symmetry Coordination Cage from 38- or 62-Component Self-Assembly

Artificial molecular architecture from a large number of subcomponents (>50) via self-assembly remains a formidable challenge for chemists. Reaction of 38 components [14 Ni(2+) and 24 N-methyl-1-(4-imidazolyl)methanimine] under solvothermal conditions reproducibly leads to the formation of a high-symmetry coordination cage. This polyhedral cage can also be obtained in high yield by self-assembly of 62 commercially available subcomponents (24 methylamine, 24 4-formylimidazole, and 14 Ni(2+)) under mild conditions involving synchronized formation of both dynamic covalent bonds and coordination bonds. Guest molecules (e.g., water, methylamine, and methanol) are randomly imprisoned in the cage.

Analysis of melamine cyanurate in urine using matrix-assisted laser desorption/ionization mass spectrometry.

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) was applied to the direct analysis of melamine cyanurate (MC). The three commonly used MALDI matrixes, namely, alpha-cyano-4-hydroxycinnamic acid (CHCA), sinapinic acid (SA), and 2,5-dihydroxybenzoic acid (DHB), were able to desorb/ionize melamine from MC upon N(2) laser irradiation, with CHCA showing the highest detection sensitivity in the positive mode. Only DHB and SA were able to desorb/ionize cyanuric acid from MC in the negative mode but with remarkably lower sensitivity. The method is able to detect melamine unambiguously from a small amount of MC (down to 12.5 microg) spiked into urine and was successfully applied for the rapid and sensitive detection of melamine in urine stones/residues of the samples collected from patients clinically confirmed of having kidney stones associated with the consumption of melamine-tainted food products. The urine matrix resulted in interfering ion peaks and suppressed the ion intensity of melamine, while a cleanup process consisting of simply washing with water eliminated such interference and enhanced the ion intensity. The merit of the method is simplicity in sample preparation. The analytical time of the method for high-throughput analysis from the time of sample treatment to analysis is less than 7 minutes per sample, with sensitive detection of the presence of melamine in the urine stones/residues of the patient samples.

Tissue-spray ionization mass spectrometry for raw herb analysis

Tissue-spray ionization mass spectrometry is developed for the in situ chemical analysis of raw herbs under ambient conditions. We demonstrated that analyte molecules could be directly sprayed and ionized from solvent-wetted ginseng tissues upon the application of high electrical voltage to the tissue sample. Abundant phytochemicals/ metabolites, including ginsenosides, amino acids and oligosaccharides, could be detected from ginseng tissues when the tissue-spray experiments were conducted in positive ion mode. Thermally labile and easily hydrolyzed malonyl-ginsenosides were also detected in negative ion mode. The tissue-spray ionization method enables the direct detection of analytes from raw herb samples and preserves the sample integrity for subsequent morphological and/ or microscopic examination. In addition, this method is simple and fast for chemical profiling of wild-type and cultivated-type American ginsengs with differentiation.

A novel mechanism of XIAP degradation induced by timosaponin AIII in hepatocellular carcinoma.

Inducing tumor cell death is one of the major therapeutic strategies in treating cancer. The aim of this study is to investigate the mechanism underlying the involvement of autophagy in cell death induced by timosaponin AIII (TAIII). Cell viability was determined by MTT and cologenic assay; apoptosis was determined by flow cytometry and TUNEL assay; autophagy was examined by immunoblotting and immunofluorescence; ubiquitination was detected by co-immunoprecipitation; mRNA expression was detected by real-time PCR; and determination of necrotic cell death was approached with LDH assay. The in vivo tumor growth inhibition was determined by xenograft model. TAIII exhibits potent cytotoxicity on human hepatocellular carcinoma (HCC) cells without severe hepatic toxicity. TAIII induced caspase-dependent apoptosis in HCC, and the induction of apoptosis was attributed to the inhibition of TAIII on XIAP expression. Repressing XIAP expression allowed cell tolerance toward the treatment with TAIII. The suppression of XIAP by TAIII is under post-transcriptional control and independent of proteasomal-driven proteolysis. Instead, TAIII-induced AMPKα/mTOR-dependent autophagy was responsible for XIAP suppression and triggered the XIAP heading lysosomal degradation pathway. Ubiquitination of IAPs is required for the autophagic degradation induced by TAIII. Blockade of autophagy turns on the switch of necrotic cell death in TAIII-treated cells. Timosaponin AIII induces HCC cell apoptosis through a p53-independent mechanism involving XIAP degradation through autophagy-lysosomal pathway. The possibility of developing TAIII as a new anti-tumor agent is worth considering.

Molecular imaging of banknote and questioned document using solvent-free gold nanoparticle-assisted laser desorption/ionization imaging mass spectrometry.

Direct chemical analysis and molecular imaging of questioned documents in a non/minimal-destructive manner is important in forensic science. Here, we demonstrate that solvent-free gold-nanoparticle-assisted laser desorption/ionization mass spectrometry is a sensitive and minimal destructive method for direct detection and imaging of ink and visible and/or fluorescent dyes printed on banknotes or written on questioned documents. Argon ion sputtering of a gold foil allows homogeneous coating of a thin layer of gold nanoparticles on banknotes and checks in a dry state without delocalizing spatial distributions of the analytes. Upon N(2) laser irradiation of the gold nanoparticle-coated banknotes or checks, abundant ions are desorbed and detected. Recording the spatial distributions of the ions can reveal the molecular images of visible and fluorescent ink printed on banknotes and determine the printing order of different ink which may be useful in differentiating real banknotes from fakes. The method can also be applied to identify forged parts in questioned documents, such as number/writing alteration on a check, by tracing different writing patterns that come from different pens.

Electrospray ionization on porous spraying tips for direct sample analysis by mass spectrometry: enhanced detection sensitivity and selectivity using hydrophobic/hydrophilic materials as spraying tips

RATIONALE Despite various porous materials having been widely adopted as spraying tips for direct sample analysis using electrospray ionization mass spectrometry (ESI-MS), the effect of surface property and porosity of spraying tip materials on their analytical performances is not clear. Investigation of their relationships could provide insight into the proper choice and/or design of spraying tip materials for direct sample analysis. METHODS The effect of spraying tip materials with different polarities, including polyester and polyethylene (hydrophobic) and wood (hydrophilic), on the detection sensitivity for a variety of compounds, and on the ESI onset voltage, were studied using ESI-MS. The porosity of each type of spraying tip was characterized by scanning electron microscopy (SEM). Factors governing the detection sensitivity were determined based on the correlation of the detection sensitivity to the ESI onset voltage, the polarity, and the porosity of the spraying tip materials. RESULTS Hydrophobic tips (i.e., polyester and polyethylene) show better detection sensitivity for polar compounds but not for non-polar compounds, while hydrophilic tips (wooden tips) show the opposite effect. This phenomenon could be due to the difference in interaction between the analytes and the tips, causing the analytes to adsorb on the tip to different extents. In addition, the micro-porous nature of the tips could facilitate solvent diffusion for transporting analytes to the tip and maintain a stable spray for recording MS data. With the proper choice of spraying tip materials, trace amount of analytes at the picomole level can be detected with minimal sample pretreatment. CONCLUSIONS Both the polarity and the porosity of the spraying tip materials could significantly affect detection sensitivity for a wide variety of analytes. With proper choice of spraying tip material, ESI on a porous spraying tip could be a sensitive method for the direct analysis of daily life samples.

From supramolecular organoplatinum(II) nanowires to platinum-containing nanocomposites.

Sorting themselves out: Organometallic supramolecular nanowires are self-assembled from hybrid cyclometalated Pt(II) complexes and used as templates or precursors for various nanocomposites, such as Pt@SiO(2) nanotubes and Pt@carbon nanolayers.