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Xiangqun Zeng

Publications and source records attributed to Xiangqun Zeng.

8 recordsLinked to original sources
PubMed2006

Ionic liquid high-temperature gas sensor array.

A novel sensor array using seven room-temperature ionic liquids (ILs) as sensing materials and a quartz crystal microbalance (QCM) as a transducer was developed for the detection of organic vapors at ambient and elevated temperatures. Ethanol, dichloromethane, benzene, and heptane were selected as representative gas analytes for various kinds of environmental pollutants and common industrial solvents. The QCM/IL sensors responded proportionately and reversibly to the organic vapor concentrations (i.e., ethanol, heptane, and benzene) in the gas phase from 0 to 100% saturation at room and elevated temperatures (e.g., 120 degrees C) but deviated from this linear relationship at high concentrations for dichloromethane, a highly volatile compound. Linear discriminant analysis was used to analyze the sensing patterns. Excellent classifications were obtained for both known and unknown concentrations of vapor samples. The correct classifications were 100% for known concentration samples and 96% for samples with unknown concentrations. Thermodynamics and ATR-FT-IR studies were conducted to understand specific molecular interactions, the strength of the interaction between ILs and organic vapors, and the degree of ordering that takes place upon dissolution of the vapors in ILs. The different response intensity of the QCM/IL sensors to the organic vapors depends on the different solubilities of organic vapors in ILs and varying molecular/ion interactions between each organic vapor and IL. The diverse set of IL studied showed selective responses due to structural differences. Therefore, a sensor array of ILs would be able to effectively differentiate different vapors in pattern recognitions, facilitating discrimination by their distinctive patterns in response to organic vapors in both room and high temperatures.

Hot Temperature↗
PubMed2006

Nonregeneration protocol for surface plasmon resonance: study of high-affinity interaction with high-density biosensors.

Surface plasmon resonance (SPR) has been used in determining kinetics and thermodynamics of biological interaction in the past decades. One difficulty encountered in this technology is the need for a proper regeneration, which means the removal of analytes from the bound complexes to regenerate the activity of the ligands. Regeneration is not always practical since the harsh regeneration reagents may destroy the bioactivity of the ligands. It is even more difficult for complexes with high affinity constants. In this paper, we report a nonregeneration protocol for SPR techniques in which subsequent ligand/analyte interactions can be measured without regeneration; thus ligand biological activity could be retained. Kinetics, binding models, and mathematics of this protocol are discussed in detail using rabbit IgG as the analyte and engineered recombinant antibody A10B single-chain fragment variables (scFv) as the ligand. The affinity constant of rabbit IgG binding with A10B scFv measured by using a nonregeneration protocol was (2.5 +/- 0.2) x 10(7) M(-1), which was comparable with the value determined with a conventional regeneration SPR method ((2.2 +/- 1.5) x 10(7) M(-1)) and quartz crystal microbalance (1.9 x 10(7) M(-1)). A paradigm of streptavidin-biotin binding was analyzed to validate this protocol. The affinity constant for each binding subunit of streptavidin to the immobilized biotin was determined to be (7.3 +/- 0.2) x 10(6) M(-1), which was comparable with the solution-based value of 2 x 10(7) M(-1). The nonregeneration protocol requires a relatively high ligand density on the biosensor surface so that more data points can be obtained before surface saturation. The small size of scFv enables them to be constructed in the biosensors for such purpose.

Animals↗
PubMed2006

Carbohydrate-protein interactions by "clicked" carbohydrate self-assembled monolayers.

A Huisgen 1,3-dipolar cycloaddition "click chemistry" was employed to immobilize azido sugars (mannose, lactose, alpha-Gal) to fabricate carbohydrate self-assembled monolayers (SAMs) on gold. This fabrication was based on preformed SAM templates incorporated with alkyne terminal groups, which could further anchor the azido sugars to form well-packed, stable, and rigid sugar SAMs. The clicked mannose, lactose, and alpha-Gal trisaccharide SAMs were used in the analysis of specific carbohydrate-protein interactions (i.e., mannose-Con A; ECL-lactose, alpha-Gal-anti-Gal). The apparent affinity constant of Con A binding to mannose was (8.7 +/- 2.8) x 10(5) and (3.9 +/- 0.2) x 10(6) M(-1) measured by QCM and SPR, respectively. The apparent affinity constants of lactose binding with ECL and alpha-Gal binding with polyclonal anti-Gal antibody were determined to be (4.6 +/- 2.4) x 10(6) and (6.7 +/- 3.3) x 10(6) M(-1), respectively by QCM. SPR, QCM, AFM, and electrochemistry studies confirmed that the carbohydrate SAM sensors maintained the specificity to their corresponding lectins and nonspecific adsorption on the clicked carbohydrate surface was negligible. This study showed that the clicked carbohydrate SAMs in concert with nonlabel QCM or SPR offered a potent platform for high-throughput characterization of carbohydrate-protein interactions. Such a combination should complement other methods such as ITC and ELISA in a favorable manner and provide insightful knowledge for the corresponding complex glycobiological processes.

Carbohydrates↗
PubMed2005

Engineered recombinant single-chain fragment variable antibody for immunosensors.

A recombinant single-chain fragment variable (scFv) antibody (designated A10B) was engineered to contain two histidines within the linker peptide used to join the scFv heavy and light chains. A piezoimmunosensor using the scFv was successfully developed. A10B scFv bound to the gold piezoimmunosensor surface were correctly oriented, retained antigen-binding activity, and coupled at high surface concentration. These results, and results obtained from an earlier study using an scFv containing a linker cysteine, suggest that the location on the linker sequence in which the amino acids were incorporated was well tolerated by the scFv and did not interfere with scFv antigen-binding activity. The scFv-modified QCM sensor was thoroughly characterized and used to specifically detect antigen in crude serum sample and had a sensitivity of 2.3 +/- 0.15 nM (n = 4) with a linear range over 2.3 x 10(-9) - 3.3 x 10(-(8) M. The piezoimmunosensor was also used to study the kinetics and thermodynamics of antigen/scFv antibody binding.

Amino Acid Sequence↗
PubMed2005

Adsorption of 1,10-phenanthroline within a dodecanethiol monolayer: an approach to a switchable electrode surface.

A simple method was used to prepare a "switchable" electrode surface by using self-assembled monolayers of dodecanethiol on a gold electrode. The dodecane-modified electrode was electrochemically inactive until the monolayer was soaked in solutions of 1,10-phenanthroline or 2,2'-bipyridine. The electroactive form of the electrode could be reverted back to the nonelectroactive form by rinsing the electrode. Surface IR results showed that both dodecanethiol and 1,10-phenanthroline exist in the mixed monolayer.

2,2'-Dipyridyl↗
PubMed2005

Ionic liquid high temperature gas sensors.

An ionic liquid piezoelectric gas sensor was demonstrated for detection of polar and nonpolar organic vapors at high temperature with fast linear and reversible response.

Biosensing Techniques↗
PubMed2005

Single-chain fragment variable antibody piezoimmunosensors.

In this paper, we describe a novel nonlabeled biosensor with high diagnostic potential for rapid and sensitive detection of antigens in complex biological samples. The biosensor comprises a piezoimmunosensor (PZ) displaying a specially constructed recombinant antibody on its surface. The recombinant single-chain fragment variable (scFv) antibody contained a cysteine within the linker amino acid sequence used to join the scFv variable heavy and light chains. The presence of cysteine induced the scFv construct to self-assemble as a densely packed rigid monolayer on the gold surface of a quartz crystal microbalance. scFv molecules in this self-assembled monolayer (SAM) exhibited a defined orientation and high areal densities, with scFv-modified microbalance surfaces displaying 35 times as many variable antigen-binding sites per square centimeter as surfaces modified with whole antibody. Experimental data show that the scFv SAM PZ is superior to Fab fragment, Fab fragment containing a free sulfhydryl group (i.e., Fab-SH), and whole antibody PZs regarding sensitivity and specificity. Because of their small uniform size (MW approximately 27000) and the ease with which they can be modified using genetic engineering, scFv's have significant advantages over whole antibodies in microbalance biosensor systems. We demonstrate here that the use of scFv containing a cysteine within the scFv linker sequence (i.e., scFv-cys) for preparation of biosensor surfaces markedly increases the density of available antigen-binding sites, yielding a system that is highly selective, rapid, and capable of detecting low concentrations of antigens in complex samples.

Amino Acid Sequence↗