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Biomedical subjects

Baohong Liu

Publications and source records attributed to Baohong Liu.

At least 19 recordsLinked to original sources
PubMed2007

Multianalyte immunoassay based on insulating-controllable PoPD film at arrayed electrodes integrated on a silicon chip.

A novel, simple and label-free multianalyte immunoassay system is presented here by integrating arrayed electrodes on a silicon chip via MEMS. The chip is consisted of six Au disk electrodes, an Au counter electrode and an Ag/AgCl reference electrode. Semi-insulating poly(o-phenylenediamine) (PoPD) was utilized to co-polymerize and immobilize antibodies at the arrayed Au electrodes, and wider linear detection range was obtained than those prepared with completely insulating PoPD. Electrochemical cyclic voltammogram (CV), AC impedance spectroscopy, AFM and fluorescence microscopy were employed to characterize the system. The arrayed electrodes offered exact control of deposition position via electrochemical operation, allowing selectively immobilization of different antibodies at desired positions on a single chip. Specific recognition of antibody (Ab) to corresponding antigen (An) was quantitatively monitored by cyclic voltammograms in the presence of electrochemical redox probe, ferrocene methanol. The proposed immunoassay chips showed sensitive response to three liver fibrosis markers, hyaluronic acid (HA), collagen type IV (IV-C) and lamin (LN) at ng/mL level simultaneously and specifically in a tiny amount of volume, usually 50 microL. The results obtained via chips were well consistent with those obtained by commercial radio immunoassays (RIA).

Antigens↗
PubMed2006

Assembly-controlled biocompatible interface on a microchip: strategy to highly efficient proteolysis.

A biocompatible interface was constructed on a microchip by using the layer-by-layer (LBL) assembly of charged polysaccharides incorporating proteases for highly efficient proteolysis. The controlled assembly of natural polyelectrolytes and the enzyme-adsorption step were monitored by using a quartz-crystal microbalance and atomic force microscopy (AFM). Such a multilayer-assembled membrane provides a biocompatible interconnected network with high enzyme-loading capacity. The maximum digestion rate of the adsorbed trypsin in a microchannel was significantly accelerated to 1600 mM min(-1) microg(-1), compared with the tryptic digestion in solution. Based on the Langmuir isotherm model, the thermodynamic constant of adsorption K was calculated to be 1.6 x 10(5) M(-1) and the maximum adsorption loading Gammamax was 3.6 x 10(-6) mol m(-2), 30 times more than a monolayer of trypsin on the native surface. The tunable interface containing trypsin was employed to construct a microchip reactor for digestion of femtomoles of proteins and the produced peptides were analyzed by MALDI-TOF mass spectroscopy. The efficient on-chip proteolysis was obtained within a few seconds, and the identification of biological samples was feasible.

Biocompatible Materials↗
PubMed2006

Photosynthetic reaction center functionalized nano-composite films: effective strategies for probing and exploiting the photo-induced electron transfer of photosensitive membrane protein.

Photosynthetic reaction center (RC), a robust transmembrane pigment-protein complex, works as the crucial component participating the primary event of the photo-electrochemical conversion in bacteria. Sparked by the high photo-induced charge separation yield (ca. 100%) of RC, great interests have been aroused to fabricate versatile RC-functionalized nano-composite films for exploring the initial photosynthetic electron transfer (ET) of RC, and thus exploiting well-designed bio-photoelectric converters. In this review, we classify and summarize the current status about the concepts and methods of constructing RC-immobilized nano-composite films or devices for probing the photo-induced ET, and applying to novel bioelectronics if it is possible.

Biosensing Techniques↗
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

Deposition of PEG onto PMMA microchannel surface to minimize nonspecific adsorption.

A protein-resistant surface has been constructed on the poly(methyl methacrylate) (PMMA) microfluidic chips based on a one-step modification. The copolymer of butyl methacrylate (BMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) is synthesized to introduce a dense PEG molecular brush-like coating on the PMMA microchannel surfaces via the anchoring effect of the hydrophobic BMA units. The PEGMA segments could produce hydrophilic domains formed on the interface so as to achieve stable electroosmotic flow, and less nonspecific adsorption toward biomolecules. The modification procedure and the properties of the poly(BMA-co-PEGMA)-coated surface have been characterized by FT-IR spectroscopy, confocal fluorescence microscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. The water contact angle and electroosmotic flow of PEG-modified PMMA microchip are measured to be 36 degrees and 5.4 x 10(-4) cm(2) V(-1) s(-1), while those of 73 degrees and 1.9 x 10(-4) cm(2) V(-1) s(-1) for native one, respectively. The PEG-modified microchip has been applied for the electrophoresis separation of proteins, corresponding to the theoretical efficiencies about 16 300 and 412 300 plates m(-1). In the interest of achieving efficient separation while minimizing biofoulings from the serum and plasma, the fabrication of PEG-coated microfluidic chips would provide a biocompatible platform for complex biological analysis.

Adsorption↗
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↗
PubMed2006

On-chip chiral separation based on bovine serum albumin-conjugated carbon nanotubes as stationary phase in a microchannel.

A novel method of chiral separation based on protein-stationary phase immobilized in a poly(methyl methacrylate) microfluidic chip was developed. BSA conjugated with the shortened carboxylic single-walled carbon nanotubes (SWNTs) was employed as the chiral selector. Successful separation of tryptophan enantiomers was achieved in less than 70 s with a resolution factor of 1.35 utilizing a separation length of 32 mm. This is the first example of chiral separation based on SWNTs-BSA conjugates as stationary phase immobilized in microchip channel. The stability of the stationary phase in the channel was examined by microchip electrophoresis with laser-induced fluorescence detection. Factors that influenced the chiral separation resolution were examined. Under the optimized conditions, the proposed modified chip revealed adequate repeatability concerning run-to-run. These results show that the use of SWNTs-BSA conjugates within microfluidic channels hold great promise for a variety of analytical schemes.

Carbon↗
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↗