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PubMed1997

Studies towards a disposable screen-printed amperometric biosensor for progesterone.

A screen-printed carbon electrode (SPCE) has been investigated as the base transducer for a disposable amperometric progesterone biosensor. The biorecognition element was a monoclonal sheep anti-progesterone antibody (mAb). This was immobilized onto the transducer by interaction with a layer of rabbit IgG which had been previously coated onto the SPCE; optimum conditions for these loadings were deduced experimentally. The device was employed in a competitive assay using alkaline phosphatase-labelled progester-one. Three possible substrates for the enzyme were considered, namely, phenyl phosphate, phenolphthalein phosphate and 4-aminophenol phosphate. Cyclic voltammetry and amperometry were carried out on the corresponding aromatic phenols and phenol itself was found to give the best electrochemical characteristics; consequently, phenyl phosphate was employed as the substrate. Chronoamperometry was used to measure the phenol produced by the reaction of bound enzyme-labelled progesterone and substrate. The chronoamperometric response was dependent on unlabelled progesterone over at least three orders of magnitude with a detection limit of about 1 x 10(-9) mol/dm3. This suggests that the device may have applications for the analysis of biological fluids.

Aminophenols↗
PubMed1999

A comparison of 1-naphthyl phosphate and 4 aminophenyl phosphate as enzyme substrates for use with a screen-printed amperometric immunosensor for progesterone in cows' milk.

4-Aminophenyl phosphate (4-APP) and 1-naphthyl phosphate (1-NP) were compared as enzyme substrates for an amperometric milk progesterone biosensor utilising progesterone-conjugated alkaline phosphatase in a competitive immunoassay format. Cyclic voltammetry of the corresponding hydrolysis products, 4-aminophenol and 1-naphthol, at the surface of screen-printed carbon base transducers, uncoated or coated with anti-progesterone monoclonal antibody (mAb) showed well-defined anodic responses for both species, with the more sensitive being 4-aminophenol. Scan rate studies produced evidence that surface mAb could impede the diffusion of 4-aminophenol, but not 1-naphthol, toward the electrode surface. This was supported by computer simulation for the electrochemical rate constant (khet) using 4-aminophenol, which gave values at uncoated and mAb-coated electrodes of 6.5 x 10(-4) and 3.0 x 10(-4) cm s-1, respectively. The applied potential for oxidation of 4-aminophenol was 230 mV lower than for 1-naphthol. Nevertheless, by operating below +400 mV versus a saturated calomel reference electrode, it was possible to obtain a chronoamperometric signal for 1-naphthol in the absence of electrochemical interference from milk. Using mAb-coated SPCEs, calibration curves were obtained for progesterone in oestrus whole cow's milk spiked with standard concentrations over the range 0-50 ng/ml, using either 4-APP or 1NP as enzyme substrate. Precision values for triplicate sensors were 5.3-18.3% for 4-APP and 4.1-12.4% for 1-NP. An assay of real whole milk samples from different cows at various stages of the oestrus cycle produced correlations against a commercial EIA of r = 0.840 and 0.946 for 4-APP and 1-NP, respectively, 1-NP possesses the advantages over 4-APP of being inexpensive, easy to obtain and soluble (1-naphthol cf. 4-aminophenol) at high pH. From these observations, it is concluded that 1-NP is the preferred substrate for use with our proposed milk progesterone biosensor.

Alkaline Phosphatase↗
PubMed2004

Women are silver, women are diamonds: conflicting images of women in the Cambodian print media.

This paper examines 116 articles related to sexual and reproductive health translated into English from the Khmer press from April 1997 to February 2004. These excerpts were found in The Mirror, a publication of the non-governmental organisation Open Forum of Cambodia, which collates and reviews all issues of the Khmer press on a weekly basis. Five major themes were identified: the politics of women's health, government regulation and control, the sex industry in Cambodia, rape, and the HIV epidemic. Discourse analysis of these articles in the context of other sources and experience allows a gendered exploration of the reporting of sexual and reproductive health and rights issues in Cambodia by the Khmer print media. The reports explore the contested political empowerment of women in this strongly hierarchical society, and the mechanisms used to regulate and control sexual activity The expanding sex industry and associated sexual trafficking are reported, together with the corruption of legal structures designed to regulate health systems and protect women and children from sexual exploitation and rape. The growing problem of AIDS and successes in reducing HIV transmission through the collaboration of sex workers in the 100% condom use policy is documented, and the tensions implicit in a cultural representation of women that both protects and constrains women are explored.

Cambodia↗
PubMed2001

137Cs contained in books printed during the 1960s in Japan.

Radioactivity values of 137Cs in printed pages and covers of hardbound books issued during the 1960s in Japan were measured by gamma-ray spectrometry. The result showed that the main source of 137Cs present in the books was rice straw used to make the backing board of covers. The 1965 peak of 137Cs content of the book was explained by the variation of 137Cs content of rice straw with the harvest year and a change of the kind of board.

Journal Article↗
PubMed1999

Isolation of azo-dye-degrading microorganisms and their application to white discharge printing of fabric.

Three bacterial strains, which degraded azo dyes, were isolated from soil and sewage samples. The strains were identified as Bacillus sp. OY1-2, Xanthomonas sp. NR25-2 and Pseudomonas sp. PR41-1. The bacteria produced azo-dyes-degrading enzymes. That catalyzed the reduction of methyl red and produced dimethyl p-phenylenediamine and o-aminobenzoic acid. The enzymes could thus be applied to white discharge printing of azo-dyed fabric by owing to there.

Journal Article↗
PubMed2002

Selective detection of o-diphenols on copper-plated screen-printed electrodes.

Selective detection of o-diphenols (e.g., catechol, dopamine, and pyrogallol) in the presence of simple phenols, m- and p- derivative diphenols, and ascorbic acid has been demonstrated on copper-plated screen-printed electrodes (CuSPEs) in pH 7.4 phosphate buffer solution. The CuSPE showed an unusual catalytic response at -0.05 V versus Ag/AgCl selectively to o-diphenolic compounds. The o-diphenols can thus be determined amperometrically through direct electrochemical oxidation in low potentials (approximately 0 V), where the CuSPE is much less subject to interfering reactions. Such a catalytic phenomenon cannot be observed on conventional Pt and glassy carbon electrodes. The selective mechanism is explained in terms of the formation of cyclic five-member complex intermediate (Cu(II)-o-quinolate). Most important of all, the common drawbacks of electrode fouling through polymerization were completely overcome in this system.

Ascorbic Acid↗
PubMed2002

Photoelectrochemical oxygen sensor using copper-plated screen-printed carbon electrodes.

We report here an efficient photocatalytic amperometric sensor for the determination of dissolved oxygen (DO) in phosphate buffer solution using a disposable copper-plated screen-printed carbon electrode (CuSPE). The photoelectrochemical activity toward DO of the CuSPE was related to the formation of a p-type semiconductor Cu(I)2O. The solution pH and biased potential (E(bias)) were systematically optimized as pH 8 PBS and -0.7 V vs Ag/AgCl, respectively. Under optimized conditions, the calibration plot was linear in the range of 1-8 ppm with sensitivity and regression coefficient of 23.51 (microA cm2)(-1) ppm(-1) and 0.9982, respectively. The reproducibility of the system was good with seven successive measurements of DO yielding a RSD value of 1.87%. Real sample assays for groundwater and tap water were also consistent with those measured by a commercial DO meter. The principle used in DO measurement has an opportunity to extend into various research fields.

Carbon↗
PubMed2003

Flow injection analysis of an ultratrace amount of arsenite using a Prussian blue-modified screen-printed electrode.

We report here a new electrochemical method for the selective detection of ultratrace amount of arsenite (AsO(2)(-), As(3+)) using a Prussian blue-modified screen-printed electrode (designated as PBSPE) by flow injection analysis (FIA) in 0.1 M, pH 4 KCl/HCl carrier solution. The Prussian yellow/Prussian blue redox couple of the PBSPE was found to mediate the As(3+) oxidation. Various factors influencing the determination of As(3+) were thoroughly investigated in this study. Under the optimized FIA conditions, a linear calibration plot in the range of 50 nM-300 microM with a detection limit (S/N = 3) of 25 nM (i.e., 64.9 pg in 20-microL loop) was observed at an operation potential of +0.6 V vs Ag/AgCl. The sensitivity was good enough to detect arsenite at levels lower than the current EPA standard. This modified electrode showed good resistance to interference from common ions, especially Cl(-), which is generally considered as a major interference in the determination of As(3+) by ICPMS. The practical utility of the PBSPE to detect As(3+) was demonstrated in "blackfoot" disease endemic village groundwater from the southwestern coast area of Taiwan (Pei-Men).

Journal Article↗
PubMed2003

Photoelectrocatalytic oxidation of o-phenols on copper-plated screen-printed electrodes.

A novel and sensitive detection method based on photoelectrocatalytic oxidation of o-diphenols was demonstrated on a copper-plated screen-printed carbon electrode (designated CuSPE) in pH 8 phosphate buffer solution. The o-diphenols can be detected amperometrically through electrochemical oxidation at a low applied potential of -0.1 V versus Ag/AgCl, where the CuSPE is much less subject to interfering reactions. The mechanism that induces good selectivity of the CuSPE is explained in terms of the formation of a cyclic five-member complex intermediate (Cu(II)-o-quinolate). A prototype homemade flow through cell design is described for incorporating the photoelectrode and light source. Electrode irradiation results in a large increase in anodic current. The oxidative photocurrents produced by irradiation increase with light intensity presumably because of the formation of semiconductor Cu(2)O. The principle used in this study has an opportunity to extend into various research applications.

Journal Article↗
PubMed2003

A dry process for production of microfluidic devices based on the lamination of laser-printed polyester films.

A new microfabrication process based on a xerographic process is described. A laser printer is used to selectively deposit toner on a polyester film, which is subsequently laminated against another polyester film. The toner layer binds the two polyester films and allows the blank regions to become channels for microfluidics. These software-outlined channels are approximately 6 microm deep. Approximately twice this depth is obtained by laminating two printed films. The resulting devices were not significantly damaged after 24 h of exposure to aqueous solutions of H3PO4, NaOH, methanol, acetonitrile, or sodium dodecyl sulfate. Electric tests with an impedance analyzer and microchannels filled with KCl solution demonstrated that (1) wide channels suffer from deformation of the top and bottom walls due to the lamination of the polyester films and (2) the toner walls are somewhat porous. Although these drawbacks limit the maximum width of a channel and the minimum distance between two channels, the process is an attractive option to other expensive, laborious, and time-consuming methods for microchannels fabrication. The process has been used to implement devices for electrospray tip and capillary electrophoresis with contactless conductivity detection.

Journal Article↗
PubMed2004

Printed circuit technology for fabrication of plastic-based microfluidic devices.

One of the primary advantages of using plastic-based substrates for microfluidic systems is the ease with which devices can be fabricated with minimal dependence on specialized laboratory equipment. These devices are often produced using soft lithography techniques to cast replicas of a rigid mold or master incorporating a negative image of the desired surface structures. Conventional photolithographic micromachining processes are typically used to construct these masters in either thick photoresist, etched silicon, or etched glass substrates. The speed at which new masters can be produced using these techniques, however, can be relatively slow and often limits the rate at which new device designs can be built and tested. In this paper, we show that inexpensive photosensitized copper clad circuit board substrates can be employed to produce master molds using conventional printed circuit technology. This process offers the benefits of parallel fabrication associated with photolithography without the need for cleanroom facilities, thereby providing a degree of speed and simplicity that allows microfluidic master molds with well-defined and reproducible structural features to be constructed in approximately 30 min in any laboratory. Precise control of channel heights ranging from 15 to 120 microm can be easily achieved through selection of the appropriate copper layer thickness, and channel widths as small as 50 microm can be reproducibly obtained. We use these masters to produce a variety of plastic-based microfluidic channel networks and demonstrate their suitability for DNA electrophoresis and microfluidic mixing studies.

DNA↗
PubMed2004

Enzymatic genosensor on streptavidin-modified screen-printed carbon electrodes.

Voltammetric enzyme genosensors on streptavidin-modified screen-printed carbon electrodes (SPCEs) for the detection of virulence nucleic acid determinants of pneumolysin and autolysin genes, exclusively present on the genome of the human pathogen Streptococcus pneumoniae, were described. Alkaline phosphatase (AP) and 3-indoxyl phosphate were used as the enzymatic label and substrate, respectively. The oligonucleotide probes were immobilized on electrochemically pretreated SPCEs through the streptavidin/biotin reaction. The adsorption of streptavidin was performed by deposition of a drop of a streptavidin solution overnight at 4 degrees C on the surface of the SPCEs. After the hybridization reaction with FITC-labeled complementary targets, the enzyme is captured using an anti-FITC antibody conjugated to AP. In nonstringent experimental conditions, these genosensors can detect 0.49 fmol of 20-mer oligonucleotide target and discriminate between a complementary oligo and an oligo with a three-base mismatch. In the presence of 25% formamide in the hybridization buffer, a single-base mismatch on the oligonucleotide target can be detected.

Adsorption↗
PubMed2006

Fabrication of a planar-form screen-printed solid electrolyte modified Ag/AgCl reference electrode for application in a potentiometric biosensor.

This study features the fabrication of a planar-form, solid electrolyte modified, (PSEM) Ag/AgCl reference electrode using a screen-printing method. The PSEM Ag/AgCl reference electrode uses agar gel as the inner electrolyte and chloroprene rubber for the liquid junction and insulator. These common low-cost materials and the simple fabrication processes involved render the proposed reference electrode an ideal candidate for cost-efficient mass production. It is shown that the developed reference electrode is insensitive to most of the physiologically important ionic species, including Na+, K+, Li+, Ca2+, NH4+, and Cl-, under continuous measurement conditions. Moreover, as with conventional commercial reference electrodes, the proposed reference electrode exhibits a reversible response, which is maintained until the agar gel dries out. The PSEM Ag/AgCl reference electrode is integrated with an iridium oxide modified Pt-based pH indicator electrode to form a chip-type pH biosensor. The performance of this biosensor is consistent with that obtained from a pH meter based on a macroscopic commercial Ag/AgCl reference electrode. The experimental results confirm that the proposed biosensor is capable of providing precise pH measurements of various real samples. Accordingly, the PSEM Ag/AgCl reference electrode presented in this study provides a viable alternative to the macroscopic Ag/AgCl reference electrode used in many conventional chip-based pH sensors.

Biosensing Techniques↗
PubMed2006

Antioxidant redox sensors based on DNA modified carbon screen-printed electrodes.

Antioxidant redox sensors based on DNA modified carbon screen-printed electrodes were developed. The carbon ink was doped with TiO2 nanoparticles, onto which double-strand DNA was adsorbed. A redox mediator, namely, tris-2,2'-bipyridine ruthenium(II) [Ru(bpy)3(2+)] was electrooxidized on the electrode surface to subsequently oxidize both the adsorbed ds-DNA and the antioxidants in solution. The resulting oxidation damage of the adsorbed ds-DNA was then detected by square wave voltammetry in a second solution containing only Ru(bpy)3Cl2 at a low concentration (microM). A kinetic model was developed to study the protecting role of antioxidants in aqueous solutions. The electrochemical sensor has been applied to evaluate the redox antioxidant capacity of different molecules.

Antioxidants↗
PubMed1998

Diffraction-based cell detection using a microcontact printed antibody grating.

An optical detector has been fabricated that is specific for targeted bacterial cells, by stamping an antibody grating pattern on a silicon surface. The antibody grating alone produces insignificant optical diffraction, but upon immunocapture of cells, the optical phase change produces a diffraction pattern. This technique eliminates much of the surface modifications and the secondary immunochemical or enzyme-linked steps that are common in immunoassays. Microcontact printing provides an alternative to previously reported photolithographic-mediated antibody patterning processes and uses a photolithographic process simply to produce the elastomeric stamp. We have stamped antibodies directly onto clean native oxide silicon substrates with no other chemical surface treatments. Direct binding of the antibodies to the silicon occurs in a way that still allows them to function and selectively bind antigen. The performance of the sensor was evaluated by capturing Escherichia coli O157:H7 cells on the antibody-stamped lines and measuring the intensity of the first-order diffraction beam resulting from the attachment of cells. The diffraction intensity increases in proportion to the cell density bound on the surface.

Antibodies↗
PubMed1999

An immunomagnetic electrochemical sensor based on a perfluorosulfonate-coated screen-printed electrode for the determination of 2,4-dichlorophenoxyacetic acid.

A disposable immunomagnetic electrochemical sensor involving a magnetic particle-based solid phase and a Nafion film-coated screen-printed electrode (Nafion-SPE) stuck at the bottom of a polystyrene cylinder (microwell of 300 microL) was developed and evaluated in a competitive immunoassay of the widely used herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The competitive binding of 2,4-D and 2,4-D labled with alkaline phosphatase (AP) for a limited amount of polyclonal anti-2,4-D antibody-coated magnetic beads was monitored electrochemically by measuring the AP labled++ activity bound to the beads. The phosphoric acid ester of [[(4-hydroxyphenyl)amino]-carbonyl]cobaltocenium hexafluorophosphate was used as the AP substrate. This anionic substrate (S-) is enzymatically transformed at pH 9.0 into a cationic phenol derivative (P+) which can be easily accumulated in the polyanionic Nafion coating and determined by cyclic voltammetry. During the enzyme reaction, the AP-associated beads were localized on the surface of the Nafion-SPE with the aid of a magnet, thus effectively increasing the concentration of P+ in the Nafion-modified electrode vicinity. The enzyme generation of P+ close to the electrode surface, and thereby to the Nafion film, resulted in a high amplification of the response. A detection limit of 0.01 microgram L-1 2,4-D was thus achieved. The performance of the sensor was successfully evaluated on river water samples spiked with 2,4-D, indicating that this convenient and sensitive technique offers great promise for decentralized environmental applications.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2000

Electrochemistry in nanovials fabricated by combining screen printing and laser micromachining

The coupling of screen-printing and laser micromachining technology has been used to create a nanovial with "built-in" working and reference electrodes. The volume of the nanovial was calculated to be 7.2 nL using dimensions determined by SEM. The electrochemical nanovial was characterized using the ferri/ferrocyanide redox couple. Cyclic voltammetry and chronoamperometry experiments were performed with electrochemical nanovials utilizing 5% (v/v) glycerin in the solutions and a humidified headspace to control evaporation of the small-volume samples. Chronoamperometry experiments gave results consistent with a diffusion-limited process and revealed a working electrode surface area of 2.6 x 10(4) micron 2. The ultrasmall-volume cells represent a simple, reliable, low-cost approach for the fabrication of complete electrochemical nanovials.

Journal Article↗
PubMed2003

Leaching of lead from computer printed wire boards and cathode ray tubes by municipal solid waste landfill leachates.

The proper management of discarded electronic devices (E-waste) is an important issue for solid waste professionals because of the magnitude of the waste stream and because these devices often contain a variety of toxic metals (e.g., lead). While recycling of E-waste is developing, much of this waste stream is disposed in landfills. Leaching tests are frequently used to characterize the potential of a solid waste to leach when disposed in a landfill. In the United States, the Toxicity Characteristic Leaching Procedure (TCLP) is used to determine whether a solid waste is a hazardous waste by the toxicity characteristic. The TCLP is designed to simulate worse-case leaching in a landfill environment where the waste is co-disposed with municipal solid waste (MSW). While the TCLP is a required analysis from a regulatory perspective, the leachate concentrations measured may not accurately reflect the concentrations observed under typical landfill conditions. Another method that can be performed to assess the degree a pollutant might leach from a waste in a landfill is to use actual landfill leachate as the leaching solution. In this study, two lead-containing components found in electronic devices (printed wire boards from computers and cathode ray tubes from computers and televisions) were leached using the TCLP and leachates from 11 Florida landfills. California's Waste Extraction Test (WET) and the Synthetic Precipitation Leaching Procedure were also performed. The results indicated that the extractions using MSW landfill leachates resulted in lower lead concentrations than those by the TCLP. The pH of the leaching solution and the ability of the organic acids in the TCLP and WET to complex with the lead are factors that regulate the amount of lead leached.

Electronics↗