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Biomedical subjects

Baohong Liu

Publications and source records attributed to Baohong Liu.

18 recordsLinked to original sources
PubMed2006

Construction of a biomimetic surface on microfluidic chips for biofouling resistance.

A biomimetic surface has been formed on the poly(methyl methacrylate) (PMMA) microfluidic chips for biofouling resistance on the basis of a simple modification. Accordingly, an amphiphilic phospholipid copolymer of 2-methacryloyloxyethyl phosphorylcholine and n-butyl methacrylate (PMB) was developed to introduce the phosphorylcholine functional groups onto the PMMA surface via the anchoring of hydrophobic n-butyl methacrylate units. The 2-methacryloyloxyethyl phosphorylcholine segments could form hydrophilic domains, considered to be located on the surface, to provide a biocompatible surface. X-ray photoelectron spectroscopy and Fourier transform infrared spectra confirmed the success of surface functionalization. The PMB-modified microchips containing phosphorylcholine moieties exhibited more stable electroosmotic mobility compared with the untreated one. In addition to being characterized for minimized nonspecific adhesion of serum proteins and plasma platelets, the PMB-functionalized microchannels have been exemplified by electrophoresis of proteins. This one-step procedure offers an effective approach for a biomimetic surface design on microfluidic chips, which is promising in high-throughput and complex biological analysis.

Biomimetics↗
PubMed2006

Zeolite nanoparticle modified microchip reactor for efficient protein digestion.

An enzymatic microreactor has been fabricated based on the poly(methyl methacrylate) (PMMA) microchchip surface-modified with zeolite nanoparticles. By introducing the silanol functional groups, the surface of PMMA microchannel has been successfully modified with silicalite-1 nanoparticle for the first time due to its large external surface area and high dispersibility in solutions. Trypsin can be stably immobilized in the microchannel to form a bioreactor using silica sol-gel matrix. The immobilization of enzyme can be realized with a stable gel network through a silicon-oxygen-silicon bridge via tethering to those silanol groups, which has been investigated by scanning electron microscopy and microchip capillary electrophoresis with laser-induced fluorescence detection. The maximum proteolytic rate constant of the immobilized trypsin is measured to be about 6.6 mM s(-1). Using matrix assisted laser desorption and ionization time-of-flight mass spectrometry, the proposed microreactor provides an efficient digestion of cytochrome c and bovine serum albumin at a fast flow rate of 4.0 microL min(-1), which affords a very short reaction time of less than 5 s.

Amino Acid Sequence↗
PubMed2006

Multilayer-assembled microchip for enzyme immobilization as reactor toward low-level protein identification.

A microchip reactor has been developed on the basis of a layer-by-layer approach for fast and sensitive digestion of proteins. The resulting peptide analysis has been carried out by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Natural polysaccharides, positively charged chitosan (CS), and negatively charged hyaluronic acid (HA) were multilayer-assembled onto the surface of a poly(ethylene terephthalate) (PET) microfluidic chip to form a microstructured and biocompatible network for enzyme immobilization. The construction of CS/HA assembled multilayers on the PET substrate was characterized by AFM imaging, ATR-IR, and contact angle measurements. The controlled adsorption of trypsin in the multilayer membrane was monitored using a quartz crystal microbalance and an enzymatic activity assay. The maximum proteolytic velocity of the adsorbed trypsin was approximately 600 mM/min mug, thousands of times faster than that in solution. BSA, myoglobin, and cytochrome c were used as model substrates for the tryptic digestion. The standard proteins were identified at a low femtomole per analysis at a concentration of 0.5 ng/muL with the digestion time <5s. This simple technique may offer a potential solution for low-level protein analysis.

Adsorption↗
PubMed2006

Controlled nanozeolite-assembled electrode: remarkable enzyme-immobilization ability and high sensitivity as biosensor.

An enzyme-immobilized nanozeolite-assembled electrode was prepared by controlled assembly of nanometer-sized Linder type-L zeolite (nano-LTL-zeolite) on an indium tin oxide (ITO) glass electrode surface, and subsequent immobilization of cytochrome c. Cyclic voltammetric (CV) and amperometric experiments showed that, relative to other reported electrodes, the enzyme-immobilized electrodes possess fast electron-transfer rates (2.2 s(-1)), a broad linear range (15-540 micromol L(-1)), a low detection limit (3.2 nmol L(-1)), a remarkably long lifetime (5 months), and high stability in the pH range 5-10. These characteristics could be due to the fact that nanozeolites assembled on ITO have high immobilization ability and facilitate interaction with enzymes. The function controllability of these enzyme electrodes, resulting from the facile manipulability of nanozeolite-assembled layers, may provide a possibility to rationally design biosensors.

Biosensing Techniques↗
PubMed2005

Immunoassays based on microelectrodes arrayed on a silicon chip for high throughput screening of liver fibrosis markers in human serum.

A novel immunoassays for screening of disease markers in human serum are presented by miniaturizing interdigitated array (IDA) of microelectrodes via micro electro-mechanical system (MEMS) on a silicon chip for multi-channel electrochemical measurement. Different selected antibodies (Abs) are incorporated site-specifically into the electrochemically deposited polypyrrole (PPy) formed on the IDA of the silicon chip, which was characterized by fluorescence microscope photo and the electrochemical quartz crystal microbalance (EQCM) measurements. The selective recognition of Ab to the corresponding antigen (Ag) is monitored through the measurable conductivity change, which is directly visualized by cyclic voltammograms (CVs) in presence of the redox probe, Fe (CN)6(3-/4-). By using the strategy presented here, three liver fibrosis markers, hyaluronic acid (HA), lamin (LN) and collagen type IV (IV-C), are detected simultaneously and specifically at the surface of the chip with calibration curves, y = 21.75 + 0.84x (R = 0.995), y = 57.54 + 0.47x (R = 0.999) and y = 37.92 + 0.28x (R = 0.999), separately. Either the standard or the serum samples can be detected at ng/mL concentration level in a tiny amount of volume, approximately 50 microL. The chip-based immunoassay shows the advantages of high sensitivity, good specificity, high throughput, low sample consumption, and the stability offered via batch production by MEMS as well, which is expected to benefit the multi-target screening of desired clinical analytes.

Biomarkers↗
PubMed2005

Photoelectric performance of bacteria photosynthetic proteins entrapped on tailored mesoporous WO3-TiO2 films.

Novel three-dimensional wormlike mesoporous WO(3)-TiO(2) films with tailored pore size (approximately 7.1 nm) were applied to prepare the bio-photoelectrodes (Bio-PEs) through direct entrapping the bacteria photosynthetic reaction center (RC) proteins. These mesoporous WO(3)-TiO(2) films exhibited unique characteristics in the specific loading of RC with high activity retained. Moreover, well-matched energy levels of WO(3)-TiO(2) and RC contributed to the photoelectric performance, especially in the red to near-infrared (NIR) region, of the derived Bio-PEs. Such strategy of manipulating the Bio-PEs based on well-designed mesoporous metal oxides and RC provides an alternative system to probe the photoinduced multiple-pathway electron transfer of photosensitive chromophores, which may open a new perspective to develop versatile bio-photoelectric devices.

Adsorption↗
PubMed2005

Controlled switchable surface.

The macroscopic properties of a surface can be intelligently controlled by alternating the states of the modified molecules, such as polymers, metallic oxide, or self-assembled monolayers (SAMs). This article reviews various approaches to create a switchable surface and different types of external stimuli used to switch the surface properties. This area is of potential benefit for biomaterials, biosensors, information storage, microfluidic systems, adhesive materials, nanolithography, and so on.

Journal Article↗
PubMed2004

Microfluidic enzymatic-reactors for peptide mapping: strategy, characterization, and performance.

The design and characterization of two kinds of poly(dimethylsiloxane)(PDMS) microfluidic enzymatic-reactors along with their analytical utility coupled to MALDI TOF and ESI MS were reported. Microfluidic devices integrated with microchannel and stainless steel tubing (SST) was fabricated using a PDMS casting technique, and was used for the preparation of the enzymatic-reactor. The chemical modification was performed by introducing carboxyl groups to PDMS surface based on ultraviolet graft polymerization of acrylic acid. The covalent and physical immobilization of trypsin was carried out with the use of the activation reagents 1-ethyl-3-(3-dimethyl aminopropyl)carbodiimide(EDC)/N-hydroxysuccinimide (NHS) and a coupling reagent poly(diallyldimethylammonium chloride)(PDDA), respectively. The properties and success of processes of trypsin immobilization were investigated by measuring contact angle, infrared absorption by attenuated total reflection spectra, AFM imaging and electropherograms. An innovative feature of the microfluidic enzymatic-reactors is the feasibility of performing on-line protein analysis by embedded SST electrode and replaceable tip. The lab-made devices provide an excellent extent of digestion of several model proteins even at the fast flow rate of 3.5 microL min(-1) for the EDC/NHS-made device and 0.8 microL min(-1) for the PDDA-made device, which afford very short residence times of 5 s and 20 s, respectively. In addition, the lab-made devices are less susceptive to memory effect and can be used for at least 50 runs in one week without noticeable loss of activity. Moreover, the degraded PDDA-made device can be regenerated by simple treatment of a HCl solution. These features are the most required for microfluidic devices used for protein analysis.

Dimethylpolysiloxanes↗
PubMed2004

Stable microstructured network for protein patterning on a plastic microfluidic channel: strategy and characterization of on-chip enzyme microreactors.

Chemical modification of a poly(methyl methacrylate) (PMMA) microchannel surface has been explored to functionalize microfluidic chip systems. A craft copolymer was designed and synthesized to introduce the silane functional groups onto the plastic surface first. Furthermore, it has been found that, through a silicon-oxygen-silicon bridge that formed by tethering to these functional groups, a stable patterning network of gel matrix could be achieved. Thus, anchorage of proteins could be realized onto the hydrophobic PMMA microchannels with bioactivity preserved as far as possible. The protein homogeneous patterning in a microfluidic channel has been demonstrated by performing microchip capillary electrophoresis with laser-induced fluorescence detection and confocal fluorescence microscopy. To investigate the bioactivity of enzymes entrapped within stable silica gel-derived microchannels, the suggested scheme was employed to the construction of immobilized enzyme microreactor-on-a-chip. The proteolytic activity of immobilized trypsin has been demonstrated with the digestion of cytochrome c and bovine serum albumin at a fast flow rate of 4.0 microL/min, which affords the short residence time less than 5 s. The digestion products were characterized using MALDI-TOF MS with sequence coverage of 75 and 31% observed, respectively. This research exhibited a simple but effective strategy of plastic microchip surface modification for protein immobilization in biological and proteomic research.

Amino Acid Sequence↗
PubMed2004

Controlled protein assembly on a switchable surface.

The strategy presented in this work supplies a general method of controlling protein assembly on a switchable low-density SAM, which may open a new way to design functional biocomposite films for biosensors or protein chips.

Protein Engineering↗
PubMed2003

Ultrathin alumina sol-gel-derived films: allowing direct detection of the liver fibrosis markers by capacitance measurement.

A capacitive immunoassay based on antibody-embedded ultrathin gamma-alumina sol-gel films (approximately 20 to 40 nm) was successfully prepared in this work. The nanofilms greatly increased the capacitance change initiated by the recognition between the immobilized antibody and the target antigen, which allowed capacitive measurements capable of directly determining the antigen more sensitive than that of thick films. Meanwhile, the inorganic films with high permittivity significantly increased the time constant (i.e., RC value) of the films, which rendered the potentiostatic step method with acceptable S/N ratio. These two advantages enabled the immunosensor to be readily employed in a multichannel capacitance analysis system. An eight-channel hIgG capacitive sol-gel-derived immunoassay based on this system was constructed to illustrate the application. Compared with the detection limits of SiO2 sol-gel-derived hIgG capacitive immunosensors or the conventional ELISA immunoassay, the immunoassay based on thin alumina gel film showed a lower detection limit of 1 ng mL(-1). The novel immunoassay was employed to co-determine two liver fibrosis markers (hyaluronan and laminin) in mixed samples from approximately 0.5 to 50 ng mL(-1). The little derivation caused by the interfered antigen indicated that the sensitive, specific, low-cost sol-gel-derived multichannel immunosensors might be a promising approach in the application of screening disease markers.

Aluminum Oxide↗
PubMed2003

Covalently coupling the antibody on an amine-self-assembled gold surface to probe hyaluronan-binding protein with capacitance measurement.

Hyaluronan-binding proteins (HABPs), the important structural components of extracellular matrices, served important structural and regulatory functions during development and in maintaining adult tissue homestats. A sensitive, specific and rapid-responsing immunosensor to probe hyaluronan-binding cartilage protein was presented in this work. The novel immunosensor supplied a label-free detection method for HABP, which was based on measuring the capacitance change in-between the unlabeled HABP (antigen) and rabbit-anti-HABP (Ra-HABP, antibody). The HABP immunosensor was prepared by covalently coupling Ra-HABP on an amine-self-assembled gold surface with glutaraldehyde. The capacitance change corresponding to the concentration of HABP, the target antigen, was evaluated by an electrochemical approach called potentiostatic-step in microseconds. The immunosensor showed a specific response to HABP in the range 10-1000 ng/ml. The presented work supplied a promising clinical screening method.

Adsorption↗
PubMed2002

TiO2 sol-gel derived amperometric biosensor for H2O2 on the electropolymerized phenazine methosulfate modified electrode.

A novel hydrogen peroxide biosensor was developed based on the immobilization of horseradish peroxidase (HRP) in a TiO(2) sol-gel matrix on an electropolymerized phenazine methosulfate (PMS) modified electrode surface. Such membranes are of interest due to their high surface area, biological compatibility, and ease of fabrication. HRP entrapped in the TiO(2) matix was stable and retained its activity to a large extent. Cyclic voltammetry and amperometric measurements were employed to demonstrate the feasibility of electron transfer between immobilized HRP and the glassy carbon electrode via electropolymerized PMS. The influence of various experimental parameters such as operating potential, pH, temperature, and stability was investigated for optimum analytical performance. The biosensor provided a wide linear calibration range from 4.0x10(-6) M to 1.0x10(-3) M, with a detection limit of 8.0x10(-7) M at a signal-to-noise ratio of 3. The sensor retained 80% of its original activity after two months of operation.

Biosensing Techniques↗
PubMed2002

A BOD biosensor based on a microorganism immobilized on an Al2O3 sol-gel matrix.

A novel BOD biosensor has been fabricated from a microbial membrane on an oxygen electrode; a porous inorganic Al2O3 sol-gel matrix was used to immobilize the yeast. Use of the sensor is convenient and rapid compared with the official BOD5 method. The gelation time required to form the microorganism membrane was less than 15 min. There was linear relationship between the response (sensor current) and BOD values ranging from 10-50 mg x L(-1). The lifetime of the BOD biosensor was more than 30 days at ambient temperature.

Aluminum Oxide↗
PubMed2002

Differentiating the orientations of photosynthetic reaction centers on Au electrodes linked by different bifunctional reagents.

The photosynthetic reaction center (RC) composite film was fabricated by self-assembled monolayers (SAMs) on the Au electrode with two different bifunctional reagents, 4-aminothiophenol (ATP) and 2-mercaptoethylamine (MEA), respectively. The square wave voltametry (SWV), bulk electrolysis and photocurrent test were employed for characterizing the composite film. The dramatic different electrochemical characteristics were observed for the two types of films, which strongly suggested an orientational difference for RC arising from the structural difference between the two bifunctional reagents. For RC-MEA film, three redox peaks which implying electron transfer (ET) between the primary donor (P) and the bacteriopheophytin (Bphe) were observed. While for RC-ATP film, two redox peaks implying ET between the nonheme iron and the primary quinone (Q(A)) were observed. The ET behavior driven by electric field also supported the result that the RC could be linked to the electrode at different sites. The site-specific immobilization approach reported here supplies a method to differentiate the protein orientation.

Aniline Compounds↗
PubMedDate not supplied

Titania and alumina sol-gel-derived microfluidics enzymatic-reactors for peptide mapping: design, characterization, and performance.

The design and characterization of titania-based and alumina-based Poly(dimethylsiloxane) (PDMS) microfluidics enzymatic-reactors along with their analytical features in coupling with MALDI-TOF and ESI-MS were reported. Microfluidics with microchannel and stainless steel tubing (SST) were fabricated using PDMS casting and O(2)-plasma techniques, and were used for the preparation of an enzymatic-reactor. Plasma oxidation for the PDMS microfluidic system enabled the channel wall of the microfluidics to present a layer of silanol (SiOH) groups. These SiOH groups act as anchors onto the microchannel wall linked covalently with the hydroxyl groups of trypsin-encapsulated sol matrix. As a result, the trypsin-encapsulated gel matrix was anchored onto the wall of the microchannel, and the leakage of gel matrix from the microchannel was effectively prevented. A feature of the microfluidic enzymatic-reactors is the feasibility of performing on-line protein analysis by attached SST electrode and replaceable tip. The success of trypsin encapsulation was investigated by AFM imaging, assay of enzymatic activity, CE detection, and MALDI-TOF and ESI-MS analysis. The lab-made devices provide an excellent extent of digestion even at a fast flow rate of 7.0 microL/min, which affords the very short residence time of ca. 2 s. With the present device, the digestion time was significantly shortened compared to conventional tryptic reaction schemes. In addition, the encapsulated trypsin exhibits increased stability even after continuous use. These features are required for high-throughput protein identification.

Aluminum Oxide↗
PubMedDate not supplied

Strategy for allosteric analysis based on protein-patterned stationary phase in microfluidic chip.

An effective method is presented for the on-chip analysis of chiral interactions with a successful depression of nonspecific adsorption. The alumina gel-derived protein network on poly(methyl methacrylate) (PMMA) microchannel was explored to form a protein-stationary phase and then used to carry out electrophoresis for fast enantioseparation coupled with electrochemical detection. On the basis of the chemical modification of a synthesized copolymer containing silane-functionalized scaffold, alumina sol-gel could react readily with the silane groups and form steady microstructure on the chip surface achieving the encapsulation of functional biomolecules. Compared with the native PMMA microchannels, the modified surfaces exhibited much better wettability, more stable and enhanced electroosmotic mobility, and less nonspecific adsorption. The water contact angle and EOF of alumina-gel-derived PMMA substrate were 22 degrees and 4.3 x 10(-4) cm(2) V(-1) s(-1), compared to those of 73 degrees and 1.9 x 10(-4) cm(2) V(-1) s(-1) from the untreated one, respectively. Bovine serum albumin, acting as a target protein, could be stably and homogeneously immobilized in the modified PMMA microchannel to fabricate a protein-stationary phase. Under a mild condition, D- and L-tryptophan were efficiently separated with a resolution of 1.57. The as-prepared microchip can perform chiral separations within short time, indicating that the general protocol has the potential to provide a platform for high throughput screening of enantiomer candidates such as those biochemical drugs with protein targets and the research of receptor interactions.

Adsorption↗