Biomedical subjects

Yunqing Chen

Publications and source records attributed to Yunqing Chen.

5 recordsLinked to original sources

PubMed2007

Characterization of anhydrous and hydrated pharmaceutical materials with THz time-domain spectroscopy.

The identification of anhydrous and hydrated forms of pharmaceutical substances is of great importance in pharmaceutical science and industry. We report the use of THz time-domain spectroscopy (THz-TDS) for pseudopolymorph investigation. The anhydrous forms of pharmaceutical substances including caffeine, theophylline, D-glucose, and ampicillin exhibit different THz absorption spectra from their hydrated forms, presumably due to their different intermolecular vibrational modes mediated by hydrogen-bonding. The data from X-ray powder diffractometry (XRPD) confirm the crystallinity differences between the anhydrous and hydrated forms. The temperature-dependent THz spectra of caffeine hydrate were also recorded, and it demonstrates that THz-TDS can be used to monitor the dehydration process of drug hydrates. We conclude that THz-TDS is an advantageous technique for the pseudopolymorph identification and study, and has great potential to become a process analytical technology (PAT) in pharmaceutical production and quality control.

Ampicillin↗

PubMed2006

Quantitative intracellular molecular profiling using a one-dimensional flow system.

We report on the development of one-dimensional microfluidic bead arrays for rapid and quantitative molecular profiling of human cancer cells. This new bioanalytical platform integrates the rapid binding kinetics of suspension bead carriers, the multiplexing and encoding capabilities of gene/protein chips, and the liquid handling advantages of microfluidic devices. Using antibody-conjugated beads in a two-site "sandwich" format, we demonstrate that the proteomic contents of as few as 56 human lung epithelial cancer cells can be determined with high sensitivity and specificity. The results indicate that each cell contains approximately 6 x 10(5) copies of the tumor suppressor protein P53. We have further examined the expression changes of P53, c-Myc, and beta-Actin as a function of anticancer drug treatment and have validated these changes by using Western blotting. This ability to quantitatively analyze normal and diseased cells raises new possibilities in studying cancer heterogeneity and circulating tumor cells.

Animals↗

PubMed2006

Sensing minute changes in biological cell monolayers with THz differential time-domain spectroscopy.

We used terahertz differential time-domain spectroscopy (THz-DTDS) to measure minute changes of bovine lung microvessel endothelial cells (BLMVEC) in response to vascular endothelial growth factor (VEGF). These changes were reflected by alterations in THz wave attenuations and THz dielectric properties of the treated cells. The VEGF-induced THz attenuations of cell monolayers correlated well with changes in transendothelial resistance, as measured using electric cell-substrate impedance sensing (ECIS). However, the morphological differences that gave rise to these changes were not observed with standard optical phase contrast microscopy. We conclude that THz-DTDS is a highly sensitive, non-invasive, powerful new tool to measure minute changes in the morphology of live, cultured cell monolayers. This method enables spectroscopic investigations of cells in the THz band, providing information unavailable through other conventional methods such as optical phase contrast microscopy and ECIS.

Animals↗

PubMed2004

Nanoscale probing of the enamel nanorod surface using polyamidoamine dendrimers.

Although it is known that noncollagenous proteins of dental origin bind to the hydroxyapatite crystal surfaces, no measure of their binding strength has been calculated. This experiment used -COOH-capped generation 7 PAMAM dendrimers as nanoprobes of the biological hydroxyapatite nanorod surfaces. Dendrimer distribution was characterized using AFM. The results showed dendrimers to be spaced at intervals along the c-axis of the crystals. From these observations and assuming a fully ionized -COOH dendrimer, a mathematical model of the binding capacity of the crystal surface with the dendrimer was developed. The Monte Carlo method was used to simulate the binding process between the dendrimer and crystal surface, and the binding strength of the -COOH groups to the surface was calculated to be 90 +/- 20 kJ/mol. These results support the CFM studies which have described alternating bands of charge domains on the crystal surface and that the binding strength will be dependent on both the intensity of the charge on the protein and the crystal surface.

Dendrimers↗

PubMed2003

Mixed C18 and C1 modification on an optical fiber for chromatographic sensing.

An optical fiber-chromatographic sensor, aiming at simultaneous and selective response to multiple components following a chromatographic separation, is described. We report an improved approach for immobilization of octadecyl (C(18)) and methyl (C(1)) moieties as stationary phase on an optical fiber suitable as a sensing phase for organic solutes. By this approach, the stability and lifetime of the sensing layer as well as the detectability and retention behavior of the chromatographic sensor could be improved. Infrared spectroscopy was employed to confirm the presence of C(18) and C(1) moieties on the modified surface of the optical fiber. The chromatographic sensor was applied, with good sensitivity and chemical selectivity, to the simultaneous separation and detection of bromobenzene and toluene, using water as the mobile phase.

Biosensing Techniques↗