Fabrication of a polystyrene microfluidic chip coupled to electrospray ionization mass spectrometry for protein analysis.

A highly integrated polystyrene (PS) microfluidic chip coupled to electrospray ionization mass spectrometry for on-chip protein digestion and online analysis was developed. The immobilized enzymatic microreactor for on-chip protein digestion was integrated onto microchip via the novel method of region-selective UV-modification combined with glutaraldehyde-based immobilization. The micro film electric contact for applying high voltage was prepared on chips by using UV-directed electroless plating technique.

A microfluidic chip capable of switching W/O droplets to vertical laminar flow for electrochemical detection of droplet contents.

Analysis of droplet contents is a key function involved in droplet-based microfluidic systems. Direct electrochemical detection of droplet contents suffers problems such as relatively poor repeatability, interference of capacitive current and relatively poor detectability. This paper presents a novel hybrid polydimethylsiloxane-glass chip for highly sensitive and reproducible amperometric detection of droplet contents.

Preparation of hybrid soda-lime/quartz glass chips with wettability-patterned channels for manipulation of flow profiles in droplet-based analytical systems.

Profile switching of two-phase flows is often required in microfluidic systems. Manipulation of flow profiles can be realized by control of local surface energy of micro channel through wettability-patterning of channel surface. This article presents a facile approach for wettability-patterning of the micro channels of glass chips.

Method for fabrication of paper-based microfluidic devices by alkylsilane self-assembling and UV/O3-patterning.

This work presents a novel and facile method for fabricating paper-based microfluidic devices by means of coupling of hydrophobic silane to paper fibers followed by deep UV-lithography. After filter paper being simply immersed in an octadecyltrichlorosilane (OTS) solution in n-hexane for 5 min, the hydrophilic paper became highly hydrophobic (water contact angle of about 125°) due to the hydrophobic OTS molecules were coupled to paper's cellulose fibers. The hydrophobized paper was then exposed to deep UV-lights through a quartz mask that had the pattern of the to-be-prepared channel network.

UV-ablation nanochannels in micro/nanofluidics devices for biochemical analysis.

This paper presents a simple and cost-effective UV-ablation technique for fabrication of size-tunable nanofluidics devices via photochemical decomposition reaction. UV-irradiation through a PET photomask results in continuous decomposition of poly(carbonate) (PC), forming nanochannel and carboxyl groups on the surface of the etched PC. This photochemical decomposition process occurs at molecular scale, therefore, the depth of nanochannels can be controlled at nanometer level.

Thermomodulated cell culture∕harvest in polydimethylsiloxane microchannels with poly(N-isopropylacrylamide)-grafted surface.

Cell culture and harvest are the most upstream operation for a completely integrated cell assay chip. In our previous work, thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) was successfully grafted onto polydimethylsiloxane (PDMS) surface via benzophenone-initiated photopolymerization. In the present work, the PNIPAAm-grafted-PDMS (PNIPAAm-g-PDMS) surface was explored for thermomodulated cell culture and noninvasive harvest in microfluidic channels.

Thermoswitchable electrokinetic ion-enrichment/elution based on a poly(N-isopropylacrylamide) hydrogel plug in a microchannel.

This paper reports a novel protocol consisting of the thermomodulated electrokinetic enrichment, elution, and separation of charged species based upon a thermoswitchable swelling-shrinking property of a poly(N-isopropylacrylamide), PNIPAAm, hydrogel. A 0.2-1 mm long PNIPAAm hydrogel plug was photopolymerized inside a glass microfluidic channel to produce a composite device consisting of the PNIPAAm hydrogel plug and the glass microchannel (abbreviated as plug-in-channel).

On-chip integrated multi-thermo-actuated microvalves of poly(N-isopropylacrylamide) for microflow injection analysis.

An array of thermo-actuated poly(N-isopropylacrylamide) (PNIPAAm) multivalves was designed and fabricated to perform volume-based sample injection for microflow injection analysis on a glass microfluidic chip. The PNIPAAm monolithic plug valves were prepared inside the vinylized glass channels by photopolymerization in water-ethanol (1:1) medium using 2-hydroxy-2-methyl propiophenone (Darocure-1173) as the initiator and a photo-mask for micropattern transferring. Experimental conditions for the photopolymerization were studied, and the thermo-responsive behavior of the synthesized monolithic plug valves was investigated.

Preparation of micro gold devices on poly(dimethylsiloxane) chips with region-selective electroless plating.

A novel protocol for fabrication of micro gold devices on poly(dimethylsiloxane) (PDMS) substrates was developed on the basis of region-selective electroless plating. The layout of a micro gold device was first photochemically patterned onto the PDMS surface through a UV induced poly(acrylic acid) (PAA) grafting process. The carboxylic moieties on the grafted PAA served as the scaffold for a series of wet chemical reactions that led to the immobilization of gold nanoparticles in the UV-exposed region, where electroless plating then occurred under the catalysis of the nanoparticles.

Fracture mechanism of metal electrode integrated on a chip and fabrication of a poly(ethylene terephthalate) electrophoresis microchip.

Thermal bonding is an important technique to fabricate polymer electrophoresis microchip. However, the metal electrodes deposited on polymer substrate can readily fracture during the thermal bonding. In this paper, poly(ethylene terephthalate) (PET) was exploited to fabricate the electrophoresis microchip with an integrated gold electrode for amperometric detection.

Proliferation and multi-differentiation potentials of human mesenchymal stem cells on thermoresponsive PDMS surfaces grafted with PNIPAAm.

The thermo-responsivity of PNIPAAm [poly(N-isopropylcarylamide)]-grafted PDMS [poly(dimethylsiloxane)] surface is a property that could be feasibly used for detaching cells adhered on the surface. We used benzophenone-initiated photopolymerization to graft PNIPAAm on PDMS substrates to construct the PNIPAAm-grafted PDMS surface and this PDMS surface was highly thermo-responsive. hMSCs (human mesenchymal stem cells) were used to analyse the proliferation and multi-differentiation of stem cells on the PNIPAAm-grafted PDMS surface.

Preparation and characterization of thermo-responsive PDMS surfaces grafted with poly(N-isopropylacrylamide) by benzophenone-initiated photopolymerization.

In the preparation of a thermo-responsive, poly(N-isopropylacrylamide) (PNIPAAm)-grafted polydimethylsiloxane (PDMS) surface by means of benzophenone-initiated photopolymerization, we observed that thick (>1 mm) PDMS substrates were much more difficult to be grafted with PNIPAAm than thin ones. Investigations revealed that the shortage of diffused benzophenone molecules in the surface region of the thick substrate might be the reason. By prolonging the time spent for treating the substrate with a benzophenone solution, PNIPAAm could be successfully grafted onto thick PDMS substrates.

Determination of ultra-trace amount methyl-, phenyl- and inorganic mercury in environmental and biological samples by liquid chromatography with inductively coupled plasma mass spectrometry after cloud point extraction preconcentration.

The cloud point extraction (CPE) preconcentration of ultra-trace amount of mercury species prior to reverse-phase high performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry (ICP-MS) detection was studied. Mercury species including methyl-, ethyl-, phenyl- and inorganic mercury were transformed into hydrophobic chelates by reaction with sodium diethyldithiocarbamate, and the hydrophobic chelates were extracted into a surfactant-rich phase of Triton X-114 upon heating in a water bath at 40 degrees C. Ethylmercury was found partially decomposed during the CPE process, and was not included in the developed method.

A gravity driven micro flow injection wetting film extraction system on a polycarbonate chip.

A micro flow injection wetting film liquid-liquid extraction system has been developed for trace analyte concentration and on-chip detection. A hydrophobic channel fabricated on a polycarbonate chip was used to support the wetting film, and hydrostatic pressure generated by the difference in liquid levels was employed to drive the fluids. Sequential injection of segments of aqueous sample solution and organic solvent was conducted by switching the sample- or solvent-containing vials to an on-chip sampling probe, and detection was performed by a co-focused, laser induced fluorescence detector.

Modification of amorphous poly(ethylene terephthalate) surface by UV light and plasma for fabrication of an electrophoresis chip with an integrated gold microelectrode.

Amorphous poly(ethylene terephthalate) (PET), which possess a low softening temperature (T(s)=75 degrees C), was exploited to fabricate the electrophoresis chip with an integrated gold electrode for amperometric detection, with emphases being focused on the PET surface modification via UV light and air plasma. Both UV irradiation and plasma treatment were found to be able to improve the surface wettability, enhance the supported electroosmotic flow (EOF), and increase thermal bonding strength of PET sheets, with the latter being more efficient and less time-consuming than the former in the surface modification. Upon treated with plasma for 2 min, the PET sheets could be thermally bonded at 65 degrees C.

A microchip-based flow injection-amperometry system with mercaptopropionic acid modified electroless gold microelectrode for the selective determination of dopamine.

A novel chip-based flow injection analysis (FIA) system has been developed for automatic, rapid and selective determination of dopamine (DA) in the presence of ascorbic acid (AA). The system is composed of a polycarbonate (PC) microfluidic chip with an electrochemical detector (ED), a gravity pump, and an automatic sample loading and injection unit. The selectivity of the ED was improved by modification of the gold working microelectrode, which was fabricated on the PC chip by UV-directed electroless gold plating, with a self-assembled monolayer (SAM) of 3-mercaptopropionic acid (MPA).

A high-performance polycarbonate electrophoresis microchip with integrated three-electrode system for end-channel amperometric detection.

A fully integrated polycarbonate (PC) microchip for CE with end-channel electrochemical detection operated in an amperometric mode (CE-ED) has been developed. The on-chip integrated three-electrode system consisted of a gold working electrode, an Ag/AgCl reference electrode and a platinum counter electrode, which was fabricated by photo-directed electroless plating combined with electroplating. The working electrode was positioned against the separation channel exit to reduce post-channel band broadening.

A microfluidic chip based liquid-liquid extraction system with microporous membrane.

A robust and simple approach for microfabricated chip based liquid-liquid extraction was developed for on-chip sample pretreatment. The chip based extraction system was composed of two microfabricated glass plates with a microporous membrane sandwiched in between. A simple bonding approach using epoxy was used to achieve bonding and sealing of the L-L extraction chip.

Fabrication of a gold microelectrode for amperometric detection on a polycarbonate electrophoresis chip by photodirected electroless plating.

A novel method of photoresist-free micropatterning coupled with electroless gold plating is described for the fabrication of an integrated gold electrode for electrochemical detection (ED) on a polycarbonate (PC) electrophoresis microchip. The microelectrode layout was photochemically patterned onto the surface of a PC plate by selective exposure of the surface coated without photoresist to 254 nm UV light through a chromium/quartz photomask. Thus, the PC plate was selectively sensitized by formation of reactive chemical moieties in the exposed areas.

Integrated capillary electrophoresis amperometric detection microchip with replaceable microdisk working electrode. II. Influence of channel cross-sectional area on the separation and detection of dopamine and catechol.

The interference of separation high voltage with the electrochemical detection is a major challenge to the microchip capillary electrophoresis-electrochemical detection systems with end-channel detection mode. Using dopamine and catechol as model analytes, the influences of channel cross-sectional area and channel-to-electrode distance on the high-voltage interference, accordingly on the separation and detection performances of the microchip capillary electrophoresis-electrochemical detection system were investigated. With the increase of the channel cross-sectional area from 312 through 450-615 microm2, the apparent half-wave potentials of hydrodynamic voltammetry for dopamine at the field strength of 288 V/cm shifted positively from 285 through 330-400 mV.

Electrokinetically synchronized polymerase chain reaction microchip fabricated in polycarbonate.

This paper presents a novel method for DNA thermal amplification using the polymerase chain reaction (PCR) in an electrokinetically driven synchronized continuous flow PCR (EDS-CF-PCR) configuration carried out in a microfabricated polycarbonate (PC) chip. The synchronized format allowed patterning a shorter length microchannel for the PCR compared to nonsynchronized continuous flow formats, permitting the use of smaller applied voltages when the flow is driven electrically and also allowed flexibility in selecting the cycle number without having to change the microchip architecture. A home-built temperature control system was developed to precisely configure three isothermal zones on the chip for denaturing (95 degrees C), annealing (55 degrees C), and extension (72 degrees C) within a single-loop channel.

Determination of thiamine in pharmaceutical preparations by sequential injection renewable surface solid-phase spectrofluorometry.

Fluorometric determination of thiamine requires the conversion of the analyte to fluorescent thiochrome by hexacyanoferrate(III) oxidation in alkaline solution and the isolation of the produced thiochrome from the reaction medium by solvent extraction. It was observed that thiochrome could be concentrated and separated from the reaction medium by solid-phase extraction. The thiochrome sorpted on the surface of octadecyl-alklylated poly[styrene/divinylbenzene] (C18-PS/DP) microbeads emitted strong fluorescence upon excitation, the maximum excitation and emission wavelengths being 385 nm and 433 nm, respectively.

Flow injection photochemical spectrofluorimetry for the determination of carbamazepine in pharmaceutical preparations.

Upon on-line photochemical reaction carbamazepine (CBZ) can be converted to a strong fluorescent compound which has a maximum emission wavelength of 478 nm and maximum excitation wavelength of 254 nm. Acidity of reaction medium and the acid type were found to be critical for the on-line photochemically induced fluorescence, dilute hydrochloric acid being the most suitable. Based on these observations, a flow injection photochemical spectrofluorimetric approach for determination of the drug was developed.