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Biomedical subjects

Hua-Zhong Yu

Publications and source records attributed to Hua-Zhong Yu.

17 recordsLinked to original sources
PubMed2007

DNA detection on plastic: surface activation protocol to convert polycarbonate substrates to biochip platforms.

A mild and efficient surface activation protocol to convert polycarbonate (PC) substrates, e.g., plastic bases of compact disks, to biochip platforms for DNA probe immobilization and target detection is described. The preparation procedure (activation, patterning, and coupling) is simple and effective; the on-chip hybridization is sensitive and selective. Particularly, UV/ozone treatment of PC sheets produces a hydrophilic surface with a high density of reactive carboxylic acid groups [(4.8 +/- 0.2) x 10-10 mol/cm2] in less than 10 min at ambient conditions, and no significant aging or physical damage to the substrate is observed. Covalent immobilization of DNA probes via both passive (reagent-less photopatterning and coupling in bulk solution phase) and flow-through (creation of microarrays with microfluidic channel plates) procedures has been demonstrated. Subsequent hybridization shows uniform and strong fluorescent signals for complementary target DNA and allows clear discrimination between fully complementary targets and strands with a single base-pair mismatch. The surface chemistry described herein will facilitate the development of disposable plastic biochips (not limited to DNA microarrays) and the fabrication of biomedical devices that are readable with conventional optical drives.

DNA↗
PubMed2006

Evaporation of microdroplets of ethanol-water mixtures on gold surfaces modified with self-assembled monolayers.

The wetting property and evaporation behavior of ethanol-water mixtures of various concentrations on gold surfaces modified with 1-decanethiolate self-assembled monolayers (SAMs) were studied by digital contact angle analysis. It has been shown that the initial contact angle decreases monotonically with increased concentration of ethanol in the mixture. Evaporation studies revealed a general trend with a preliminary increase in contact angle accompanied with a decrease in contact area, then a constant contact angle accompanied with a slower, linear decrease in contact area. At the very beginning of the evaporation process, the contact angles showed a rapid decrease for the microdroplets of a binary mixture with equal volume fractions (i.e., 50% ethanol). Three distinct stages of the evaporation profile for the ethanol-water mixtures were observed, which differ from the inclusive "pinning" and "shrinking" behavior observed for the pure liquid case. Ultimately, the study makes possible the use of an evaporation profile to monitor the change in concentration of a binary system and allows a better understanding of the interactions between liquid microdroplets with solid substrates.

Journal Article↗
PubMed2006

Structure and reactivity of alkoxycarbonyl (ester)-terminated monolayers on silicon: sum frequency generation spectroscopy.

Carboxylic acid-terminated monolayers on crystalline silicon surfaces can be readily modified with biological macromolecules for the fabrication of semiconductor-based biosensing devices. They were prepared by acid-catalyzed hydrolysis of alkoxycarbonyl (ester)-terminated monolayers and studied by vibrational sum frequency generation (SFG) spectroscopy. The C-H vibration region of the SFG spectra consists of strong methyl bands with significant contributions from methylene stretching modes, indicating that these monolayers are generally ordered but with considerable gauche defects in the alkyl chains in comparison with n-alkyl monolayers. After hydrolysis, the methylene stretching modes prevail, with "residues" of the methyl bands, indicating incomplete hydrolysis and disruption of the monolayer structure. This work demonstrates that SFG is capable of providing quantitative information on structure-reactivity correlations in organic monolayers.

Journal Article↗
PubMed2005

Voltammetric study of the ion-exchange binding of non-electroactive metal cations to DNA-modified surfaces.

We describe a simple electrochemical protocol for studying the ion-exchange binding of non-electroactive ions, specifically mono- and divalent metal cations of biological relevance (Mg(2+), Ca(2+), and K(+)), to DNA-modified surfaces. After incubation in a dilute solution of multiply charged transition metal complex (5.0 microM [Ru(NH(3))(6)]Cl(3)), gold electrodes modified with thiolate-DNA monolayers respond to the presence of these non-electroactive metal cations by producing significant changes in the cyclic voltammograms (i.e., decrease of the integrated charge and shift of formal potential) of the surface-bound redox complex ([Ru(NH(3))(6)](3+)). The divalent cations (particularly Mg(2+)) can be detected at very low concentrations (<10 microM), while the on-set value for K(+) is substantially higher (50 mM). The equilibrium binding constants for Mg(2+) and Ca(2+) to DNA-modified surfaces were calculated.

Animals↗
PubMed2005

Water microdroplets on molecularly tailored surfaces: correlation between wetting hysteresis and evaporation mode switching.

The evaporation of water microdroplets from solid surfaces was studied using digital contact angle analysis techniques. An inclusive trend for the evaporation process, that is, a switch from the initial constant contact area to the subsequent constant contact angle mode was observed for all surfaces examined, including mixed self-assembled monolayers (SAMs) on gold and "conventional" surfaces such as silicon wafers, polycarbonate, and Teflon. More importantly, it has been shown that the change in contact angle during the evaporation process (i.e., evaporation hysteresis, delta theta(evap), the difference between the initial and "equilibrated" contact angle) correlates well with the wetting hysteresis determined directly (i.e., measuring the advancing and receding contact angles on these surfaces by changing the drop volume). The comparison between mixed SAM surfaces and conventional solids revealed that the evaporation/wetting hysteresis is dominated by the roughness (from nanometer to micrometer scale) rather than the chemical heterogeneity of the surface. The evaporation rates of water microdroplets on these surfaces were also monitored and modeled.

Kinetics↗
PubMed2005

Kinetic control of the photochemical reactivity of hydrogen-terminated silicon with bifunctional molecules.

Carboxy-terminated crystalline silicon surfaces are of fundamental importance for biochip fabrication because of their reactivity toward biological macromolecules. To explore the feasibility of direct attachment of bifunctional molecules (e.g., omega-alkenoic acids) to hydrogen-terminated silicon crystal (H-Si) via Si-C linkages, we have investigated the photoreactivities of the alkene (-CH=CH(2)) and carboxy (-COOH) terminal groups of 1-dodecene, undecanoic acid, and undecylenic acid toward H-Si. The alkene terminus was found to react substantially faster than the carboxy terminus under UV irradiation (at 350 nm). By controlling the reaction time, high-quality carboxy-terminated monolayers, comparable to those formed by ester hydrolysis, can be obtained from a direct, one-step photochemical reaction between H-Si and undecylenic acid.

Journal Article↗
PubMed2005

Bioreactive surfaces prepared via the self-assembly of dendron thiols and subsequent dendrimer bridging reactions.

Here, we report a novel route to prepare bioreactive surfaces on gold by the self-assembly of generation-three hydroxyl-terminated dendron thiols (G3-OH) and subsequent bridging reactions using generation-two amine-terminated dendrimers (G2-NH(2)). It has been shown that G3-OH dendron thiols form a stable and uniform self-assembled monolayer on gold, which can be activated by the homobifunctional cross-linker N,N-disuccinimidyl carbonate (DSC). Subsequent derivatization of the activated monolayer via dendrimer bridging reactions with G2-NH(2) enhances the stability, reactivity, and versatility of the prepared surface. Each step of the surface formation reaction has been monitored, and the resulting surface has been characterized by wetting, electrochemistry, scanning tunneling microscopy (STM), and infrared (IR) spectroscopy measurements. The reactivity of this surface was demonstrated by a Schiff base coupling reaction with 4-cyanobenzaldehyde, by immobilizing biotin molecules onto the peripheral amine groups using one of the conjugation methods, and by further binding avidin onto the biotinylated surface. We believe that the prepared bioreactive surface with a high density of amine groups will be useful for the immobilization of biological macromolecules for various biosensor applications, such as the fabrication of DNA microarrays and protein chips.

Amides↗
PubMed2005

[Correlations of serous levels of matrix metalloproteinases (MMP-2 and MMP-9) to invasion and metastasis of papillary thyroid carcinoma].

BACKGROUND & OBJECTIVE: Papillary thyroid carcinoma is a common carcinoma in thyroid without ideal hematological biomarkers to indicate its biological feature. This study was to explore the correlation of serous levels of matrix metalloproteinases (MMP-2 and MMP-9) to invasion and metastasis of papillary thyroid carcinoma. METHODS: Serous levels of MMP-2 and MMP-9 of 74 patients with pathologically confirmed papillary thyroid carcinoma were measured by zymography. All patients were treated with modified radical operation in the Second Affiliated Hospital of Wenzhou Medical College from 1999 to 2003. RESULTS: Serous levels of activated MMP-2 and MMP-9 were significantly higher in patients with lymph node metastases than in patients without lymph node metastases (71.9+/-11.7 vs. 35.2+/-6.6, P < 0.001; 15.5+/-6.1 vs. 7.3+/-2.3, P < 0.001), and were significantly higher in patients with carcinoma invaded in and through integument than in patients with carcinoma invaded within integument (70.5+/-13.0 vs. 35.4+/-7.9, P < 0.001; 14.7+/-6.1 vs. 8.0+/-4.2, P < 0.001). There was no significant difference in serous levels of activated MMP-2 and MMP-9 between patients with carcinoma diameter of > or =1 cm and < 1 cm (55.4+/-20.4 vs. 59.3+/-20.8, 10.8+/-5.7 vs. 13.7+/-6.8). There was also no significant difference in serous levels of total MMP-2 and MMP-9 between every 2 groups mentioned above (P > 0.05). CONCLUSION: Serous levels of activated MMP-2 and MMP-9 relate with invasion and metastasis of papillary thyroid carcinoma, but not relate with tumor size.

Adolescent↗
PubMed2004

New chemistry on old CDs.

Old compact discs (CDs) have been found to be useful for modern chemical research. Their metal reflective film is suitable for the preparation of high-quality self-assembled monolayers (SAMs) and for electrochemical analysis; pre-grooved polycarbonate base is ideal for the "customized" fabrication of material micro/nanostructures; and the immobilization of biomolecules on CDs, in conjunction with a conventional CD drive, promises to be an inexpensive tool for point-of-care biomedical diagnosis and gene analysis.

Biosensing Techniques↗
PubMed2004

Kinetics of ion-exchange binding of redox metal cations to thiolate-DNA monolayers on gold.

The ion-exchange kinetics of metal cation binding to and dissociation from thiolate-DNA monolayers on gold can be monitored by a simple electrochemical protocol. The apparent first-order rate constants were obtained by analyzing the time-dependent voltammetric behavior of the redox cation [Ru(NH3)6]3+. It was found that the binding kinetics is dominated by the structural nature of the film; i.e., the apparent first-order rate constant (kapp) decreases significantly upon increasing the surface density of DNA strands. Dissociation rate constants were obtained by transferring the incubated electrode into redox-free buffer solution. The kinetic data augment our fundamental understanding of metal ion-DNA interactions and are critical to ensure the accuracy and reliability of experimental DNA detection protocols.

Cations↗
PubMed2004

Structure and reactivity of mixed omega-carboxyalkyl/alkyl monolayers on silicon: ATR-FTIR spectroscopy and contact angle titration.

The structure, reactivity, and acid-base properties of mixed monolayers prepared by photochemical reaction of hydrogen-terminated silicon with mixtures of ethyl undecylenate and n-alkenes were studied by ATR-FTIR spectroscopy and contact-angle measurements. The surface composition of the mixed monolayers and its correlation with the hydrolysis reactivity of terminal ethoxycarbonyl (ester) groups were investigated by systematically varying the mole fraction of ethyl undecylenate and the chain length of the unsubstituted alkenes in the binary deposition solution. It has been shown that the mole fraction of ester groups on the surface deviates only slightly from the mole fraction of ethyl undecylenate in the solution. The efficiency of ester hydrolysis under acidic conditions is significantly influenced by the monolayer structure, i.e., the surface density of ester groups and length of the unsubstituted alkyl chains. In addition, we find that mixed omega-alkanoic acid/alkyl monolayers on silicon (prepared via hydrolysis) exhibit well-defined contact angle titration curves from which the surface acid dissociation constants were determined. The results were compared with the acid-base properties reported in the literature for carboxylic acid-terminated alkylsiloxane monolayers on hydroxylated silicon and for omega-mercaptoalkanoic acid/alkanethiolate monolayers on gold. The weak pKa dependence (deltapKa approximately 1) on the surface density of carboxylic acid groups and on the length of unsubstituted alkyl chains is attributed to variations of the microenvironment of the acid moieties. These experimental findings provide fundamental knowledge at the molecular level for the preparation of bioreactive surfaces of controlled reactivity on crystalline semiconductor substrates.

Journal Article↗
PubMed2003

Voltammetric procedure for examining DNA-modified surfaces: quantitation, cationic binding activity, and electron-transfer kinetics.

To examine DNA-modified surfaces, we have developed a simple, convenient, and reliable procedure based on the voltammetric response of multiply charged transition metal cations (such as [Ru(NH3)6]3+) bound electrostatically to the DNA probes. At micromolar concentrations of the redox molecules in the electrolyte, the reduction and oxidation waves resulting from the immobilized cations on DNA-modified electrodes are well defined, stable, and reproducible. The surface densities of both single- and double-stranded oligonucleotides were accurately determined by integration of the peak for reduction of [Ru(NH3)6]3+ to [Ru(NH3)6]2+. In addition, the binding constant and electron-transfer rate constant of [Ru(NH3)6]3+ on DNA-modified electrodes were evaluated with the help of classical models. The present research provides not only an applicable and simple protocol for the quantitation of DNA probes on chips but also a versatile and powerful tool for the investigation of the binding activity and electron-transfer kinetics of cationic analytes on DNA-modified surfaces.

Cations↗
PubMed2003

Alkyl monolayer passivated metal-semiconductor diodes: 2: Comparison with native silicon oxide.

To understand the electrical properties at passivated metal-semiconductor interfaces, two types of mercury-insulator-silicon (n-type) junctions, Hg\C10H21-Si and Hg\SiO2-Si, were fabricated and their current-voltage and capacitance-voltage characteristics compared. Both of them exhibited near-ideal rectifying characteristics with an excellent saturation current at reverse bias, which is in contrast to the previously reported ohmic behavior of an unmodified mercury-silicon junction. The experimental results also indicated that the n-decyl monolayer passivated junction possesses a higher effective barrier height, a lower ideality factor (that is, closer to unity), and better reproducibility than that of native silicon oxide. In addition, the dopant density and build-in potential, extracted from capacitance-voltage measurements of these passivated mercury-silicon junctions, revealed that alkyl monolayer derivatization does not alter the intrinsic properties of the silicon substrate. The calculated surface state density at the alkyl monolayer\silicon interface is lower than that of the silicon oxide\silicon interface. The present study increases the possibility of using advanced organic materials as ultrathin insulator layers for miniaturized, silicon-based microelectronic devices.

Journal Article↗
PubMed2002

Templated electrochemical deposition of zirconia thin films on "recordable CDs.".

In this paper, we describe a practical method of using gold films constructed from recordable compact disks (CD-Rs) as simple, inexpensive, and micropatterned conductive substrates for the fabrication of inorganic material microstructures. Extending from their application for the fabrication of self-assembled monolayers (SAMs) reported recently, bare and SAM-modified CD-R gold substrates have been used for template-directed electrodeposition of zirconia (ZrO2) thin films (i.e., the controlled formation of zirconia thin films on the different areas of the prefabricated, micrometer mountain-valley CD-R gold substrate surfaces). The present results demonstrate that the variation of the functional groups of the selected SAMs combined with electrodynamic control can be very successful to "customize" the formation and microstructure of functional inorganic thin films, which hold promise for modern technological applications.

Journal Article↗