Fundamental Studies of Rapidly Fabricated On-Chip Passive Micromixer for Modular Microfluidics.

Micromixers play an important role in many modular microfluidics. Complex on-chip mixing units and smooth channel surfaces ablated by lasers on polymers are well-known problems for microfluidic chip fabricating techniques. However, little is known about the ablation of rugged surfaces on polymer chips for mixing uses.

Dual-opposite multi-walled carbon nanotube modified carbon fiber microelectrode for microfluidic chip-capillary electrophoresis determination of methyl parathion metabolites in human urine.

Methyl parathion (MP) is a highly toxic organophosphate and its exposure may lead to substantial adverse effects to human health. The existence of 4-nitrophenol (4-NP) in the form of free phenol, glucuronide (4-NP-G) or as a sulfate ester (4-NP-S) can be used as biomarkers to assess the duration and extent of MP exposure. In this work, a MC-CE device incorporating post-CE amperometric detection using multi-walled carbon nanotubes (MWNTs) modified carbon fiber microelectrode (CFME) was fabricated and assessed for simultaneous determination of 4-NP, 4-NP-G, and 4-NP-S in human urine.

Determination of taurine in human tear fluid by capillary electrophoresis with indirect amperometric detection based on electrogenerated bromine.

A new method for the determination of taurine was developed based on indirect amperometric detection after capillary electrophoresis. A serial dual-electrode detector comprising an on column Pt film electrode (upstream electrode) and an end column Pt microdisk electrode (downstream electrode) was utilized to conduct the indirect amperometric detection. Bromide is oxidized to bromine at upstream electrode and reduced back to bromide at downstream electrode.

A serial dual-electrode detector based on electrogenerated bromine for capillary electrophoresis.

A new serial dual-electrode detector for CE has been designed and fabricated for postcolumn reaction detection based on electrogenerated bromine. A coaxial postcolumn reactor was employed to introduce bromide reagent and facilitate the fabrication of upstream generation electrode by simply sputtering Pt film onto the outer surface of the separation capillary. Bromide introduced could be efficiently converted to bromine at this Pt film electrode and subsequently detected by the downstream Pt microdisk detection electrode.

2-D t-ITP/CZE determination of clinical urinary proteins using a microfluidic-chip capillary electrophoresis device.

To replace the time-consuming sample pretreatment procedure, a microfluidic chip-CE device incorporating on-chip sample desalting/preconcentration with transient isotachophoresis (ITP)/capillary zone electrophoresis (CZE) was fabricated to perform sequential on-chip sample pretreatment and CE determination of four urinary proteins in clinical samples. On-chip sample desalting, clean-up and analyte preconcentration enable removing interfering sample matrix prior to transferring analytes to separation capillary for transient ITP/CZE determination. Four important urinary proteins transferrin, β2-microglobulin, human serum albumin (HSA) and immunoglobulin G (IgG), investigated were shown to achieve quantitation limits sufficiently high to meet medical requirements, sensitivity enhancement up to 40-fold and detection limits down to 0.

Capillary electrophoresis with LIF detection for assessment of mitochondrial number based on the cardiolipin content.

Cardiolipin is a mitochondria-specific phospholipid known to be intimately involved with numerous mitochondrial functions. Accordingly, quantitative determination of cardiolipin provides a valuable aspect for assessing mitochondrial content and function. The current study was undertaken to develop a simple and reliable method for direct analysis of cardiolipin with particular application for the assessment of mitochondrial number of HepG2 cells.

Determination of acrylamide in potato crisps by capillary electrophoresis with quantum dot-mediated LIF detection.

Acrylamide or 2-propenamide (AAM), a water-soluble toxic contaminant, has recently caused health concern after it was found in food products made by high-temperature cooking. Due to its weak UV absorption and electrochemically inactive state, common analytical methods do not have sufficient sensitivity to meet the World Health Organization requirement. A LIF detection method mediated by water-soluble CdTe quantum dots capped with mercaptopropyl acid (MPA) is thus developed for AAM quantitation.

Capillary electrophoresis with immobilized quantum dot fluorescence detection for rapid determination of organophosphorus pesticides in vegetables.

Based on the highly sensitive and selective fluorescence enhancement of water-soluble CdTe/CdS core-shell quantum dots (QD) by organophosphorus pesticides (OPs such as mevinphos, phosalone, methidathion and diazinon), a simple, rapid and selective method is developed using CE with QD/LIF detection (473 nm excitation/532 nm fluorescence) to determine OPs in vegetable samples. The method enables the use of a simple pretreatment procedure based only on solvent extraction and eliminates the use of a time-consuming SPE step. A novel procedure is developed to immobilize QD onto the inside capillary surface via the formation of a silane coupling mercaptopropyltrimethoxysilane network.

L-cysteine-capped CdTe quantum dots as a fluorescence probe for determination of cardiolipin.

This paper described the investigation of surface-modified quantum dots (QDs) as a fluorescence probe for the detection of cardiolipin. A single-step method for preparation of non-toxic and photo-stable cadmium telluride (CdTe) QDs capped by L-cysteine in aqueous solution was developed. The prepared QDs were characterized by high-resolution transmission electron microscopy, X-ray diffraction spectrometry, Fourier transform infrared spectrometry and spectrofluorometry.

Separation and determination of metal cations in milk and dairy products by CE.

To prevent casein adsorption and improve between-run repeatability, a CE procedure is developed for cation analysis in milk using a modified imidazole/alpha-hydroxyisobutyric acid (HIBA) BGE system to operate at pH 6 to match the pH of milk and elevate imidazole concentration to enhance its buffer action. The procedure is shown to produce a fast, economic and efficient method for cation separation in milk with only simple dilution. Upon direct hydrodynamic injection of diluted milk sample at 8 cm for 30 s in an uncoated column with a BGE consisting of 10 mM imidazole, 10 mM HIBA and 10% methanol at pH 6.

Piezoelectric quartz crystal sensor for rapid analysis of pirimicarb residues using molecularly imprinted polymers as recognition elements.

A new piezoelectric quartz crystal (PQC) sensor using molecularly imprinted polymer (MIP) as sensing material has been developed for fast and onsite determination of pirimicarb in contaminated vegetables. Three MIPs particles have been prepared by conventional bulk polymerization (MIP-B) and precipitation polymerization in either acetonitrile (MIP-P1) or chloroform (MIP-P2). MIP-P2, with uniform spherical shape and mean diameter at about 50 nm, has shown the best performance as the sensing material for PQC sensor.

Variable selection for discriminating herbal medicines with chromatographic fingerprints.

When discriminating herbal medicines with pattern recognition based on chromatographic fingerprints, typically, the majority of variables/data points contain no discrimination information. In this paper, chemometric approaches concerning forward selection and key set factor analysis using principal component analysis (PCA), unweighted and weighted methods based on the inner- and outer-variances, Fisher coefficient from the between- and within-class variations were investigated to extract representative variables. The number of variables retained was determined based on the cumulative variance percent of principal components, the ratio of observations to variables and the factor indicative function (IND).

Flow analysis coupled with PQC/DNA biosensor for assay of E. coli based on detecting DNA products from PCR amplification.

A flow-through PQC/DNA biosensor system is developed by combining sequential flow polymerase chain reaction (PCR) products denaturing prior to piezoelectric quartz crystal (PQC) detection via hybridization of ssDNA. The PQC/DNA biosensor is fabricated based on complex formation of neutravidin/biotinylated probe in 0.2M NaCl in TE buffer (10mM Tris, 1mM EDTA, pH 7.

Study of adsorption behavior of bilirubin on human-albumin monolayer using a quartz crystal microbalance.

The quartz crystal microbalance was employed to study the adsorption behavior of bilirubin on human-albumin layer, which was chemically bound to the self-assembled monolayer of 4-aminothiophenol on the surface of a gold electrode of the crystal via glutaraldehyde. A long-time adsorption process of bilirubin that took place on a human-albumin-modified surface was observed, and the adsorption kinetic parameters were estimated from the in situ frequency measurements. The amount of adsorbed bilirubin increased with increasing of both hydrogen ions and bilirubin concentration and was larger than that estimated based on the conclusion that there are two affinity sites for bilirubin per albumin molecule.

Capillary zone electrophoresis characterization of low molecular weight heparin binding to interleukin 2.

A method based on capillary zone electrophoresis (CZE) was used to study the interaction between low molecular weight heparin (LMWH) and interleukin 2 (IL-2). The results showed that the increase of the concentration of LMWH led to the decrease of the peak height and the increase of the peak width of IL-2, but the peak areas were kept constant. The binding constant of IL-2 with LMWH was calculated as 1.

Rapid authentication of ginseng species using microchip electrophoresis with laser-induced fluorescence detection.

Ginseng is one of the most expensive Chinese herbal medicines and the effectiveness of ginseng depends strongly on its botanical sources and the use of different parts of the plants. In this study, a microchip electrophoresis method coupled with the polymerase chain reaction (PCR)-short tandem repeats (STR) technique was developed for rapid authentication of ginseng species. A low viscosity hydroxypropyl methylcellulose (HPMC) solution was used as the sieving matrix for separation of the amplified STR fragments.

Simultaneous and ultrarapid determination of reactive oxygen species and reduced glutathione in apoptotic leukemia cells by microchip electrophoresis.

A microchip electrophoresis method coupled with laser-induced fluorescence (LIF) detection was established for simultaneous determination of two kinds of intracellular signaling molecules (reactive oxygen species, ROS, and reduced glutathione, GSH) related to apoptosis and oxidative stress. As the probe dihydrorhodamine-123 (DHR-123) can be converted intracellularly by ROS to the fluorescent rhodamine-123 (Rh-123), and the probe naphthalene-2,3-dicarboxaldehyde (NDA) can react quickly with GSH to produce a fluorescent adduct, rapid determination of Rh-123 and GSH was achieved on a glass microchip within 27 s using a 20 mM borate buffer (pH 9.2).

Genotyping the -6A/G functional polymorphism in the core promoter region of angiotensinogen gene by microchip electrophoresis.

Angiotensinogen (AGT) gene has been regarded as one of the candidate genes for essential hypertension. In our study, the role of AGT gene as a putatively predisposing gene for hypertension was evaluated by genotyping a A (-6) G polymorphism in the core promoter region in 123 patients with essential hypertension and 103 healthy controls. A microchip electrophoresis method coupled with polymorphism chain reaction (PCR)-restriction fragment length polymorphism (RFLP) assay was used for genotyping the A (-6) G single-nucleotide polymorphism.

Determination of volatile components in ginger using gas chromatography-mass spectrometry with resolution improved by data processing techniques.

Ginger is widely used as either a food product or an herbal medicine in the world. In this paper, a method was developed for determining volatile components in essential oils from both dried and fresh ginger by use of gas chromatography-mass spectrometry (GC-MS) and chemometric approaches. With the resolution improvement by chemometric methods upon two-dimensional data from GC-MS, the drifting baseline can be corrected.

Correction of retention time shifts for chromatographic fingerprints of herbal medicines.

In this study, the combination of chemometric resolution and cubic spline data interpolation was investigated as a method to correct the retention time shifts for chromatographic fingerprints of herbal medicines obtained by high-performance liquid chromatography-diode array detection (HPLC-DAD). With the help of the resolution approaches in chemometrics, it was easy to identify the purity of chromatographic peak clusters and then resolve the two-dimensional response matrix into chromatograms and spectra of pure chemical components so as to select multiple mark compounds involved in chromatographic fingerprints. With these mark components determined, the retention time shifts of chromatographic fingerprints might be then corrected effectively.

Analysis of volatile components from Cortex cinnamomi with hyphenated chromatography and chemometric resolution.

In this paper, the combination of hyphenated chromatography and chemometric resolution was investigated as a method to qualitatively and quantitatively determine volatile components in Cortex cinnamomi from four main producing areas. With the help of chemometric resolution approaches, whether the chromatographic elution of chemical components is featured by "first-in-first-out" or embedded peaks could be determined. Upon this useful information obtained, the matrix data generated by hyphenated chromatography could be uniquely resolved into pure chromatogram and spectrum of each chemical component involved followed by qualitative and quantitative analysis.

Capillary zone electrophoresis investigation of the interaction between heparin and granulocyte-colony stimulating factor.

The interaction between standard heparin, low-molecular-weight heparin (LMWH), and granulocyte-colony stimulating factor (G-CSF) was studied by capillary zone electrophoresis. Both qualitative and quantitative characterizations of the heparin-protein binding were determined. The binding constants of the two different groups of heparins with G-CSF, calculated from the Scatchard plot by regression, were 4.

Native fluorescence detection of flavin derivatives by microchip capillary electrophoresis with laser-induced fluorescence intensified charge-coupled device detection.

To widen the scope of laser-induced fluorescence (LIF) for detection in microchip capillary electrophoresis (CE), a microchip CE LIF-ICCD (intensified charge-coupled device) system based on a tunable wavelength dye laser pumped by a pico-second pulse nitrogen laser for excitation and a spectrograph with ICCD for detection had developed to demonstrate the enhancement in detection sensitivity by the following three approaches: direct detection of native fluorescence, improvement of signal-to-noise ratio by pulse laser excitation and time delay detection, and selective spectral acquisition by multi-channel detection. Riboflavin, flavin mononucleotide (FMN) and flavin-adenine dinucleotide (FAD) have been selected as they are dietetically important and microchip CE provides a promising onsite detection method. The results indicate a strong effect of wavelength on detection sensitivity and the need to tune wavelength for direct detection.

DNA diagnosis by capillary electrophoresis and microfabricated electrophoretic devices.

DNA diagnosis is experiencing an impressive progression towards the development of novel technology to identify various clinically relevant categories of genetic changes and to meet the exponential growth of genomics. The introduction of capillary electrophoresis has dramatically accelerated the completion of the first draft of the human DNA sequence in the Human Genome Project, and thus, has become the method of choice for analysis of various genetic variants. The recent development of microfabricated electrophoretic devices has led to the possibility of integrating multiple sample handling with the actual measurement steps required for automation of molecular diagnostics.