P. Wanichapichart

Electrorotation: Diagnostic Tool for Abnormality of Marine Phytoplankton Cells

This work proposes a method to estimate cell dielectric properties using a rotating electric field. Signals given to four platinum electrodes were from a phase shift unit, which splits an input signal into four of pi/2 phase difference. The unit performs well under frequency below 5 MHz. Rotation patterns of pretreated Tetraselmis sp. were utilized to reveal dielectric information of the cells. The rotation of boiled cells diminished at the lower frequency range, while that of the arsenic pretreated cells was smaller than that of the control when higher arsenic concentration was used. The specific membrane conductance was increased from 0.5 kS.m-1 for the control to 90 kS.m-1 boiled cells. Pretreated cells with arsenic solution at 10 to 100 ppm levels increased the membrane conductance to 8.8 kS.m-1, much less effect compared to the boiled cells. Moreover, 24 hrs pretreatment was long enough for arsenic to penetrate the membrane, and the cytoplasmic permittivity was reduced from 39epsivO to about 13e0, independent of the arsenic levels used. The study can distinguish the viability from the non-viability cells by carefully selected field, frequency, and solution conductivity.

Development of traveling wave dielectrophoretic (twDEP) microfluidic system

In this work, we present a microfluidic system consisting of 16 parallel electrodes array for cell manipulation by traveling wave dielectophoretic force and electronic circuit design for creating driving signal. Polystyrene microspheres suspensions in water were used as the tested cells. Cells respond to the electric field in various mechanisms depending on the frequency of applied AC signals. When the frequency of applied AC fields is in the range where dielectrophoresis (DEP) is negative, cells experience twDEP force in such a way that they were repelled from the electrode rather than being trapped by positive DEP. The driving signals in the system are created by economical electronic circuit. As the frequency of the applied signals is in the range of 50-700 kHz, cells were move under the influence of twDEP force. As the frequency of the applied signals is more than 700 kHz, cells started moving out of the center between electrodes. These results are consistent with the theory. Because of the fact that twDEP force depends on the effective polarizability and size of particle, it gives us a chance to make the device for cells fraction and separation which can be further applied in biological and medical application such as motion control and cell selectivity.

Influence of water compositions on fouling of plane organic membrane in frontal filtration: application to water and wastewater clarification

The aim of this study was to evaluate and quantify the filterability of suspended/soluble organic and suspended inorganic matter in a condition without and with chemical conditioning on membrane fouling using cake filtration model. The experiments were conducted with different feed water concentrations under a given TMP (0.2 to 0.5 bar). The fouling potential was examined and described in terms of resistance coefficient (alpha x W) and specific resistance (alpha). The results showed an increase of alpha x W and alpha within the concentration of wastewater samples tested. The soluble fractions in wastewater induced fouling and its mechanism was due both to the interaction of soluble organic components and also some of the particular colloids in MLSS, causing irreversible fouling, followed by thin film formation on membrane surfaces with low porosity, dense structure and also internal fouling. This phenomenon promoted the values of alpha x W and alpha from final treated wastewater 5-20 times higher than in bentonite suspension and on reservoir surface water. Higher pressure than 0.2 bar induced greater hydraulic resistance values than lower applied pressure. The pore size of the porous membrane did not show any difference in the values of alpha x W and alpha obtained, but they mostly depended on the water composition tested. The hydraulic resistance values appeared largely to minimise when using chemical conditioning because of cake forming as a dynamic membrane that reduced the irreversible fouling phenomena giving a constant filtration rate.

Film Formation of Inclusion Complexes between Acetyl-Beta-Cyclodextrin and Chitosan

In this research, the films which were prepared from inclusion complexes (ICs) of acetyl-beta-cyclodextrin (Acetyl-β-CD) with chitosan were characterized and the membrane properties were investigated. Acetyl-β-CD either improved the solubility of chitosan or increased the salt rejection of the membrane. The crystalline ICs, were formed and found on the membrane surface. There were isolated and characterized by scanning electron microscopy (SEM), X-ray diffraction and atomic force microscopy (AFM). The stability and conformation of the inclusion complexes in solvent and limited number of acetyl-β-CD threaded on chitosan molecules were studied and compared the results on a molecular level of the pseudopolyrotaxane.

Cells Separation by Traveling Wave Dielectrophoretic Microfluidic Devices

In this work, we present a microfluidic device with a 16 parallel electrode array and microchamber for cell separation by using travelling wave dielectophoretic force. The dielectrophoretic PDMS chamber was fabricated using standard microfabrication techniques. The Cr/Au parallel electrode array of 100 µm wide and 300 nm thick was patterned on a glass slide by sputtering through microshadow mask. In order to test twDEP devices, two different size of polystyrene microspheres suspension in deionized water were used as the tested cells. Each type of polystyrene was tested in both the separated and mixed solution. Cells response to the electric field in various mechanisms depending on the applied voltage and frequency of AC signals. For 4.5 µm polystyrene, cells were forced to locate in the center between electrode array and move along the channel and the traveling wave dielectrophoresis occur, when the applied voltage was 10 V and the frequency of the applied signals is in the range of 50 kHz-700 kHz. For 10 µm polystyrene the twDEP occurs when the applied voltage was 7 V and frequency was in the range 30 kHz-1MHz. For the mixed solution containing equal amount of 4.5 and 10 µm microspheres, the big microspheres were moved under twDEP force when the applied voltage was 7 V and the frequency was in the range 25 kHz-1MHz while the small microspheres were attached to the electrodes. Therefore, the twDEP device can separate the microspheres with different sizes and it can be further applied for cells separation and manipulation.

An RC-Model for Dielectrophoresis of Ellipsoidal Cells: A Method for Determnination of Dielectric Properties

This work proposes an RC-model representing an ellipsoidal cell being induced in an AC electric field. The frequency dependent complex function of the induced cell dipole moment is expressed in terms of real and imaginary parts, which explains cell dielectric properties. This approach provides a simpler method so that only three values are required from experimentation. There are two critical frequencies at the lower (fclscr) and the higher (fch ) boundary which determine cross over points from negative to positive DEP force exerting on the cell and vice versa. By increasing the solution conductivity (sigmas), these frequencies converge and join as soon as the sigmas, reaches a critical value(sigmact). Under this critical conductivity the cell experiences a zero force, and the conductivity of the cytoplasm (sigmac) can be predicted. This work reveals permittivity and conductivity of the membrane and the cytoplasm of yeasts.