Edward S. Yeung

Structurally Ordered Mesoporous Carbon Nanoparticles as Transmembrane Delivery Vehicle in Human Cancer Cells

A structurally ordered, CMK-1 type mesoporous carbon nanoparticle (MCN) material was successfully synthesized by using a MCM-48 type mesoporous silica nanoparticle as template. The structure of MCN was analyzed by a series of different techniques, including the scanning and transmission electron microscopy, powder X-ray diffraction, and N2 sorption analysis. To the best of our knowledge, no study has been reported prior to our investigation on the utilization of these structurally ordered mesoporous carbon nanoparticles for the delivery of membrane impermeable chemical agents inside of eukaryotic cells. The cellular uptake efficiency and biocompatibility of MCN with human cervical cancer cells (HeLa) were investigated. Our results show that the inhibitory concentration (IC50) value of MCN is very high (>50 microg/mL per million cells) indicating that MCN is fairly biocompatible in vitro. Also, a membrane impermeable fluorescence dye, Fura-2, was loaded to the mesoporous matrix of MCN. We demonstrated that the MCN material could indeed serve as a transmembrane carrier for delivering Fura-2 through the cell membrane to release these molecules inside of live HeLa cells. We envision that further developments of this MCN material will lead to a new generation of nanodevices for transmembrane delivery and intracellular release applications.

High-sensitivity laser-induced fluorescence detection of native proteins in capillary electrophoresis

A highly sensitive laser-induced (LIF) detection scheme for native, tryptophan- or tyrosine-containing proteins in capillary electrophoresis (CE) has been demonstrated. The 275.4 nm line from an argon-ion laser is used to excite native protein fluorescence. A limit of detection (LOD) (S/N = 2) of 1 x 10(-10) M for conalbumin represents a 140-fold improvement over earlier reports. With stacking at injection, the LOD is 3 x 10(-12) M. Linear dynamic ranges of at least 5 and 4 orders of magnitude for, respectively, tryptophan and bovine serum albumin are found. The practical performance and blueprint of an easily constructed, rugged, compact and user-friendly LIF detector for CE are shown.

Non-bonded poly(ethylene oxide) polymer-coated column for protein separation by capillary electrophoresis

Abstract A simple method to coat a non-ionic hydrophilic polymer onto the inner wall of a bare fused-silica capillary is established. The capillary is first filled with l M HCl solution, then flushed with 0.2% poly(ethylene oxide) solution containing 0.1 M HCl, and finally rinsed with the electrophoretic buffer. Each step takes only 5 min. For regeneration of the coating, this procedure is repeated. Four basic proteins were separated by this method around pH 3–7 with phosphate buffer. The separation efficiency in terms of peak shape was excellent compared to bare fused-silica capillaries and comparable to many other more sophisticated column-treatment methods. The reproducibility of migration times of proteins was less than 3% R.S.D. at pH 6 by manual operation of the coating process. Titration of the fused-silica surface with acid and the structure of poly(ethylene oxide) are important factors to form a stable coating via hydrogen bonding to the surface silanol groups.

Use of mass spectrometry for imaging metabolites in plants

We discuss and illustrate recent advances that have been made to image the distribution of metabolites among cells and tissues of plants using different mass spectrometry technologies. These technologies include matrix-assisted laser desorption ionization, desorption electrospray ionization, and secondary ion mass spectrometry. These are relatively new technological applications of mass spectrometry and they are providing highly spatially resolved data concerning the cellular distribution of metabolites. We discuss the advantages and limitations of each of these mass spectrometric methods, and provide a description of the technical barriers that are currently limiting the technology to the level of single-cell resolution. However, we anticipate that advances in the next few years will increase the resolving power of the technology to provide unprecedented data on the distribution of metabolites at the subcellular level, which will increase our ability to decipher new knowledge concerning the spatial organization of metabolic processes in plants.

Photochemistry of single vibronic levels of formaldehyde

Predissociation, quenching and energy transfer have been studied for single vibrational levels of the first excited singlet state of formaldehyde (1A2). A tunable ultraviolet laser, summation of dye plus ruby, provided 7 nsec pulses with less than 1 A wavelength spread. Fluorescence decay lifetimes were measured as a function of pressure. The decay rates, extrapolated to zero pressure, increase rapidly with increasing vibrational energy. A hundredfold increase in rate is observed for 4000 cm−1 in D2CO. The variation of rate with the particular combination of normal modes excited in comparatively small. The effect of deuteration is marked; H2CO decays about twenty times faster than D2CO. We believe that for the energy range studied the only mechanism of radiationless decay compatible with the energy level structure of formaldehyde and with the lifetime observations is internal conversion to high vibrational levels of the ground state which are broadened by unimolecular dissociation. The rates measured for ...

Sensitive and Selective Detection of Copper Ions with Highly Stable Polyethyleneimine-Protected Silver Nanoclusters

Copper is a highly toxic environmental pollutant with bioaccumulative properties. Therefore, sensitive Cu(2+) detection is very important to prevent over-ingestion, and visual detection using unaugmented vision is preferred for practical applications. In this study, hyperbranched polyethyleneimine-protected silver nanoclusters (hPEI-AgNCs) were successfully synthesized using a facile, one-pot reaction under mild conditions. The hPEI-AgNCs were very stable against extreme pH, ionic strength, temperature, and photoillumination and could act as sensitive and selective Cu(2+) sensing nanoprobes in aqueous solutions with a 10 nM limit of detection. In addition, hPEI-AgNCs-doped agarose hydrogels were developed as an instrument-free and regenerable platform for visual Cu(2+) and water quality monitoring.

Indirect fluorimetric detection and quantification in capillary zone electrophoresis of inorganic anions and necleotides

Abstract The combination of indirect fluorescence detection and separation by capillary zone electrophoresis is discussed. Differences in instrument configuration, compared with earlier experiments, resulted in a reversed peak elution order. Separation of a 5′-triphosphate nucleotide from its corresponding diphosphate and monophosphate homologues can be accomplished in 5 min by this method. A quantitative comparison is made between the injection methods of electromigration and injection by gravity flow for samples of inorganic anions diluted in water with varying total concentrations. With injection of electromigration, the amount of sample injected varies significantly with the total ionic concentration of the sample.

High-Spatial and High-Mass Resolution Imaging of Surface Metabolites of Arabidopsis thaliana by Laser Desorption-Ionization Mass Spectrometry Using Colloidal Silver

High-spatial resolution and high-mass resolution techniques are developed and adopted for the mass spectrometric imaging of epicuticular lipids on the surface of Arabidopsis thaliana. Single cell level spatial resolution of approximately 12 mum was achieved by reducing the laser beam size by using an optical fiber with 25 mum core diameter in a vacuum matrix-assisted laser desorption ionization-linear ion trap (vMALDI-LTQ) mass spectrometer and improved matrix application using an oscillating capillary nebulizer. Fine chemical images of a whole flower were visualized in this high spatial resolution showing substructure of an anther and single pollen grains at the stigma and anthers. The LTQ-Orbitrap with a MALDI ion source was adopted to achieve MS imaging in high mass resolution. Specifically, isobaric silver ion adducts of C29 alkane (m/z 515.3741) and C28 aldehyde (m/z 515.3377), indistinguishable in low-resolution LTQ, can now be clearly distinguished and their chemical images could be separately constructed. In the application to roots, the high spatial resolution allowed molecular MS imaging of secondary roots and the high mass resolution allowed direct identification of lipid metabolites on root surfaces.

Indirect fluorescence detection of sugars separated by capillary zone electrophoresis with visible laser excitation

Abstract This work extends the use of indirect fluorescence detection for capillary zone electrophoresis to the visible region. Detection is based on charge displacement and is not based upon any absorption or emission properties of the analyte, therefore the need for chemical derivatization is eliminated. Capillary zone electrophoresis-indirect fluorescence detection can separate and detect almost any compound that contains a charge. This was demonstrated by the separation and detection of a mixture of sugars which are only weakly acidic. The mass detection limit of fructose was 2 fmol using a 5-μm diameter capillary. This peak had an efficiency of more than 600 000 theoretical plates.

Direct profiling and imaging of plant metabolites in intact tissues by using colloidal graphite-assisted laser desorption ionization mass spectrometry

Laser desorption/ionization (LDI)-based imaging mass spectrometry (MS) has been applied to several biological systems to obtain information about both the identities of the major chemical species and their localization. Colloidal graphite-assisted LDI (GALDI) MS imaging was introduced for the imaging of small molecules such as phospholipids, cerebrosides, oligosaccharides, flavonoids, and other secondary metabolites with high spatial homogeneity due to finely dispersed particles. Mass profiles and images of Arabidopsis thaliana have been recorded directly from various plant surfaces and cross sections. The main targeted metabolites were flavonoids and cuticular waxes, both of which are important in many aspects of functional genomics, proteomics, and metabolomics. The mass spectral profiles revealed tissue-specific accumulation of flavonoids in flowers and petals. In addition, many other location-specific ions were observed. The location and the degree of light-induced accumulation of flavonoids in stem sections were successfully probed by GALDI MS.