Biomedical subjects

Zhan Chen

Publications and source records attributed to Zhan Chen.

28 records · Page 2Linked to original sources

PubMed2004

Demonstrating the feasibility of monitoring the molecular-level structures of moving polymer/silane interfaces during silane diffusion using SFG.

In this paper, the feasibility of monitoring molecular structures at a moving polymer/liquid interface by sum frequency generation (SFG) vibrational spectroscopy has been demonstrated. N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane (AATM, NH2(CH2)2NH(CH2)3Si(OCH3)3) has been brought into contact with a deuterated poly(methyl methacrylate) (d-PMMA) film, and the interfacial silane structure has been monitored using SFG. Upon initial contact, the SFG spectra can be detected, but as time progresses, the spectral intensity changes and finally disappears. Additional experiments indicate that these silane molecules can diffuse into the polymer film and the detected SFG signals are actually from the moving polymer/silane interface. Our results show that the molecular order of the polymer/silane interface exists during the entire diffusion process and is lost when the silane molecules traverse through the thickness of the d-PMMA film. The loss of the SFG signal is due to the formation of a new disordered substrate/silane interface, which contributes no detectable SFG signal. The kinetics of the diffusion of the silane into the polymer have been deduced from the time-dependent SFG signals detected from the AATM molecules as they diffuse through polymer films of different thickness.

Journal Article↗

PubMed2003

Detection of amide I signals of interfacial proteins in situ using SFG.

In this Communication, we demonstrate the novel observation that it is feasible to collect amide signals from polymer/protein solution interfaces in situ using sum frequency generation (SFG) vibrational spectroscopy. Such SFG amide signals allow for acquisition of more detailed molecular level information of entire interfacial protein structures. Proteins investigated include bovine serum albumin, mussel protein mefp-2, factor XIIa, and ubiquitin. Our studies indicate that different proteins generate different SFG amide signals at the polystyrene/protein solution interface, showing that they have different interfacial coverage, secondary structure, or orientation.

Absorption↗

PubMed2003

Sum frequency generation studies on the surface structures of plasticized and unplasticized polyurethane in air and in water.

This study characterizes the molecular surface structures of polyurethane (PU) and plasticized PU films in air, in water, and in albumin solution in situ using a nonlinear optical technique, sum frequency generation (SFG) vibrational spectroscopy. Two different plasticizers are investigated: dioctyl sebacate (DOS) and o-nitrophenyl octyl ether (NPOE). Plasticization of PU is common for biosensors to achieve better adhesion, malleability, elasticity, and permeability; however, this can adversely affect biocompatibility. Our research indicates that plasticizers can segregate to the PU surface not only in air but also in water. In addition, plasticizer content can affect protein adsorption behaviors of PU surfaces. This is the first time surface-sensitive SFG has been applied to deduce plasticizer surface behavior in situ. More specifically, we found that DOS dominates the surface of the film with DOS surface concentrations higher than DOS bulk concentrations both in air and in contact with an aqueous environment. NPOE has a reduced effect at the surface compared to DOS in both air and aqueous environments. Addition of either DOS or NPOE to PU was also found to cause a change in albumin adsorption.

Journal Article↗

PubMed2003

The effect of surface coverage on conformation changes of bovine serum albumin molecules at the air-solution interface detected by sum frequency generation vibrational spectroscopy.

The air-BSA solution interface has been investigated by various techniques for years. From these studies we know that BSA molecules segregate at the BSA solution-air interface, and the surface coverage increases with the increase of the bulk solution concentration. However, questions still remain as to whether the protein changes conformation, orientation, or a combination of the two upon adsorption. In this paper, by using sum frequency generation (SFG) vibrational spectroscopy we found that the conformation of interfacial BSA molecules changes dramatically at the solution-air interface, compared to that of the native BSA in solution. The hydrophobic methyl groups of BSA molecules at this interface tend to align along the surface normal. The degree of such conformational changes of surface BSA molecules depend on the surface coverage, indicating that the protein-protein interaction plays a very important role in determining the conformation of interfacial protein molecules. At very low surface concentration, the adsorbed BSA molecules unfold substantially. Our results can provide a molecular interpretation of results obtained from other studies such as protein layer thickness and surface tension measurements of protein solution.

Journal Article↗

PubMed2003

Expression and identification of type 1 diabetes associated autoantigen IA-2.

OBJECTIVES: To obtain prokaryotic expressed IA-2 recombinant protein and to identify its immunological activity. METHODS: The complimentary DNA (cDNA) coding for the intracytoplasmic part of IA-2 (IA-2ic) was amplified from human fetal brain RNA, and was subcloned into the PinPoint Xa-1 T vector to construct recombinant expression plasmid, and was then expressed in E. coli JM109 cells as a fusion protein with a biotinylated peptide sequence at the aminoterminus. The biotinylated fusion protein was then purified by affinity chromatography and was subsequently dialyzed. Finally, its immunogenicity was evaluated by enzyme linked immunosorbent assay (ELISA). RESULTS: The purified IA-2ic fusion protein resolved on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) as a single Coomassie brilliant blue stained band with a molecular weight of 59 kDa and its immunogenicity was confirmed by ELISA. CONCLUSIONS: E. coli expressed IA-2ic fusion protein has immunological activity. It can be used for detection of IA-2 autoantibodies (IA-2A) and for further studies on type 1 diabetes in future.

Animals↗

PubMed2002

Molecular responses of proteins at different interfacial environments detected by sum frequency generation vibrational spectroscopy.

Sum frequency generation (SFG) vibrational spectroscopy has been applied to investigate molecular responses of bovine serum albumin (BSA) molecules adsorbed at different interfacial environments. Molecular level and in situ SFG studies demonstrate that albumin molecules have different adsorption behaviors when contact with fused silica, polystyrene, and poly(methyl methacrylate). Adsorbed albumin molecules exhibit different structural changes when exposed to different chemical environments, including air, water, and hydrophobic solvents. This paper provides direct molecular insight into protein responses to different interfacial environments.

Adsorption↗

PubMed2002

Measuring polymer surface ordering differences in air and water by sum frequency generation vibrational spectroscopy.

Molecular structures of poly(n-butyl methacrylate) (PBMA) at the PBMA/air and PBMA/water interfaces have been studied by sum frequency generation (SFG) vibrational spectroscopy. PBMA surfaces in both air and water are dominated by the methyl groups of the ester side chains. The average orientation and orientation distribution of these methyl groups at the PBMA/air and PBMA/water interfaces are different, indicating that surface restructuring occurs when the PBMA sample contacts water. Analysis shows that the orientation distribution of side chain methyl groups on the PBMA surface is narrower in water than that in air, indicating that the PBMA surface can be more ordered in water. To our knowledge, this is the first time that quantitative comparisons between molecular surface structures of polymers in air and in water have been made. Two assumptions on the orientation distribution function, including a Gaussian distribution and a formula based on the maximum entropy approach, are used in the analysis. It has been found that the orientation angle distribution function deduced by the Gaussian distribution and the maximum entropy distribution are quite similar, showing that the Gaussian distribution is a good approximation for the angle distribution. The effect of experimental error on the deduced orientational distribution is also discussed.

Journal Article↗

PubMed2002

General solution for Poisson-Boltzmann equation in semiinfinite planar symmetry.

A unique, simple, and general analytical solution for the nonlinear Poisson-Boltzmann equation in semiinfinite planar symmetry with any unmixed electrolyte is reported. This is an exact solution for symmetrical and z-2z/2z-z asymmetrical electrolytes and an approximate solution for other asymmetrical electrolytes (z-3z/3z-z or 2z-3z/3z-2z). To evaluate the accuracy of the approximate solution, the solution was compared with the numerical results obtained from the Galerkin weighted residual finite element method. The error of the approximate solution for asymmetrical z-3z/3z-z or 2z-3z/3z-2z electrolytes is not more than 1%. This new solution unifies all the cases in semiinfinite planar symmetry with any unmixed electrolyte into one expression without increasing the mathematical complexity. The general solution can serve as a functional approximation for potential distribution of two interacting electric double layers when calculating electrostatic interaction energy if the superposition approximation is used.

Journal Article↗

PubMed2002

Interaction of fibrinogen with surfaces of end-group-modified polyurethanes: a surface-specific sum-frequency-generation vibrational spectroscopy study.

Fibrinogen adsorption on polyurethanes with different surface-modifying end groups (SMEs) has been studied with sum-frequency-generation vibrational spectroscopy (SFG). The results show very different protein adsorption properties for different SMEs on the same backbone polymer. Fibrinogen binds weakly on the hydrophilic backbone of a poly(dimethyl siloxane) (PDMS)-modified polyurethane surface but leaves the hydrophobic PDMS part untouched. On sulfonate end-group-modified (SO(3(-) )) polyurethane surfaces, fibrinogen adsorbs well. However, on poly(ethylene oxide) (PEO)-modified surfaces, it adsorbs poorly. The protein-resistant character of PEO is probably due to steric repulsion. This work demonstrates the utility of SFG in the study of protein adsorption on polymeric biomaterials at the molecular level and the ability of SMEs to mediate protein adsorption.

Adsorption↗

PubMed2001

Studies of polymer surfaces by sum frequency generation vibrational spectroscopy.

Recently, sum frequency generation (SFG) vibrational spectroscopy has been developed into a powerful technique to study surfaces of polymer materials. This review summarizes the significant achievements in understanding surface molecular chemical structures of polymer materials obtained by SFG. It reviews in situ detection at the molecular level of surface structures of some common polymers in air, surface segregation of small end groups, polymer surface restructuring in water, and step-wise changed polymer blend surfaces. Studies of surface glass transition and surface structures modified by rubbing, plasma deposition, UV light irradiation, oxygen ion and radical irradiation, and wet etching are also discussed. SFG probing of polymer surfaces provides valuable insights into the relations between polymer surface structures and surface properties, which will assist in the design of polymer materials with desired surface properties.

Journal Article↗