Liding Wang

Assay of fish freshness using trimethylamine vapor probe based on a sensitive membrane on piezoelectric quartz crystal

Abstract A trimethylamine (TMA) vapor probe based on the sensitive membrane of chitosan, which encapsulated pimelic acid on piezoelectric quartz crystal has been prepared for the assay of fish freshness. The response of the probe to TMA is rapid and completely reversible at normal temperature and relatively high humidity. The probe has an exponential response to TMA in the concentration range of 5–200xa0ppm, and the relative standard deviations (R.S.D.) were less than 5% for repeated determinations of 50xa0ppm TMA within 6 months. The results of fish freshness assay were consistent with those obtained by other methods and the sensory test.

Engineering three-dimensional cardiac microtissues for potential drug screening applications.

Heart disease is one of the major global health issues. Despite rapid advances in cardiac tissue engineering, limited successful strategies have been achieved to cure cardiovascular diseases. This situation is mainly due to poor understanding of the mechanism of diverse heart diseases and unavailability of effective in vitro heart tissue models for cardiovascular drug screening. With the development of microengineering technologies, three-dimensional (3D) cardiac microtissue (CMT) models, mimicking 3D architectural microenvironment of native heart tissues, have been developed. The engineered 3D CMT models hold greater potential to be used for assessing effective drugs candidates than traditional two-dimensional cardiomyocyte culture models. This review discusses the development of 3D CMT models and highlights their potential applications for high-throughput screening of cardiovascular drug candidates.

Fabrication of a three-layer SU-8 mould with inverted T-shaped cavities based on a sacrificial photoresist layer technique

A novel method for fabricating a three-layer SU-8 mould with inverted T-shaped cavities is presented. The first two SU-8 layers were spin coated and exposed separately, and simultaneously developed to fabricate the bottom and the horizontal part of the inverted T-shaped cavity. Then, a positive photoresist was filled into the cavity, and a wet lapping process was performed to remove the excess photoresist and make a temporary substrate. The third SU-8 layer was spin coated on the temporary substrate to make the vertical part of the inverted T-shaped cavity. The sacrificial photoresist layer can prevent the first two SU-8 layers from being secondly exposed, and make a temporary substrate for the third SU-8 layer at the same time. Moreover, the photoresist can be easily removed with the development of the third SU-8 layer. A polydimethylsiloxane (PDMS) microchip with arrays of T-shaped cantilevers for studying the mechanics of cells was fabricated by using the SU-8 mould.

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. The fracture of the gold electrode was studied through FEA (finite element analysis) simulations, the potentially risk positions on the electrode were shown. The calculation results were tested by bonding experiments and were proven to be consistent with the experiments. Besides, an optimal bonding temperature for PET chip was also presented based on FEA simulations and bonding experiments. Considering the low surface properties of PET, oxygen plasma-assisted thermal bonding technique was used to enhance bonding. Upon treated for 150 s, the PET substrates could be thermally bonded at 62 degrees C without electrode fracture. The fabricated PET chips were demonstrated for detection of standard glucose solution. Satisfactory reproducibility was achieved, and the RSD values of peak height and migration time of the PET CE chips were 0.51% and 2.17%, respectively.

Deviations of Electroosmotic Fluidic Profile from Electric Double Layer Theory

The plug-like fluidic profile is one of most advantages of electroosmotic flow, which influences the reproducibility, sensitivity and separation efficiency of the microfluidic devices. Electroosmotic flow in microchannels with hydraulic diameters of less than 20 microns are investigated experimentally and qualitatively compared with prediction in electric double layer (EDL) theory. Fluidic profiles are obtained using caged-dye based technique with a high degree of resolution near the channel walls. The experimental results indicate the existence of transition zones, which is characterized by a drastic transition in velocity profile as a matching zone between the channel wall and the middle steady flow. The width scale of the transition layer was found to be the same magnitude of hydraulic diameter and much larger than the prediction in EDL theory, which is correlated with the zeta potential and length ratio of Debye length to channels hydraulic diameter, while the middle profile is influenced by pressure force and the viscidity force. The experiments indicate that the deviations from plug-like velocity profile can be avoided by the reduction of pressure gradient and the channels dimensional size

Electric Charge Measurement on Micro-Particles Suspending in Electrokinetic Microfluidic Devices

When microcolloid particles are used as seeds in biologic and chemical experiments, they are often considered to be neutral. However, our experiments have proved that the charge on seeds can be significant in electrickinetic flow even if micro- particles diameter is less than 500nm. A combination method of particle tracking velocimetry (PTV) and current method velocimetry has been proposed to measure the charge on polystyrene microparticles suspending in electrolyte. An equation between electrostatic force and Stokes-Einstein viscosity force applied on particles has been built in simply form of Basset-Boussinesq-Oseen equation. Observed mobility of particles is measured by PTV and electroosmotic mobility of the electrolyte is measured by current method velocimetry. Then the particles electrophoretic mobility is obtained. The charge on the particles can be estimated statistically from the electrophoretic mobility considering electroosmotic mobility. Experiments indicate that the charge on polystyrene latex particles with diameter of 520 nm dispersing in the 20mM borax buffer is 10.1 times 10-17 C. In the pure grain alcohol, it is 2.1 times 10-17 C. The relatively deviation is analyzed to be less than 20 percent of the measurement value. This method is very important to investigate quantificationally electrokinetic microfluidic devices and microparticles dispersing in electrolyte