Hsiang-Yu Wang

Micro-sized microbial fuel cell: A mini-review

This review presents the development of micro-sized microbial fuel cells (including mL-scale and μL-scale setups), with summarization of their advantageous characteristics, fabrication methods, performances, potential applications and possible future directions. The performance of microbial fuel cells (MFCs) is affected by issues such as mass transport, reaction kinetics and ohmic resistance. These factors are manipulated in micro-sized MFCs using specially allocated electrodes constructed with specified materials having physically or chemically modified surfaces. Both two-chamber and air-breathing cathodes are promising configurations for mL-scale MFCs. However, most of the existing μL-scale MFCs generate significantly lower volumetric power density compared with their mL-counterparts because of the high internal resistance. Although μL-scale MFCs have not yet to provide sufficient power for operating conventional equipment, they show great potential in rapid screening of electrochemically microbes and electrode performance. Additional possible applications and future directions are also provided for the development of micro-sized MFCs.

Flow-through electroporation based on constant voltage for large-volume transfection of cells.

Genetic modification of cells is a critical step involved in many cell therapy and gene therapy protocols. In these applications, cell samples of large volume (10(8)-10(9)cells) are often processed for transfection. This poses new challenges for current transfection methods and practices. Here we present a novel flow-through electroporation method for delivery of genes into cells at high flow rates (up to approximately 20 mL/min) based on disposable microfluidic chips, a syringe pump, and a low-cost direct current (DC) power supply that provides a constant voltage. By eliminating pulse generators used in conventional electroporation, we dramatically lowered the cost of the apparatus and improved the stability and consistency of the electroporation field for long-time operation. We tested the delivery of pEFGP-C1 plasmids encoding enhanced green fluorescent protein into Chinese hamster ovary (CHO-K1) cells in the devices of various dimensions and geometries. Cells were mixed with plasmids and then flowed through a fluidic channel continuously while a constant voltage was established across the device. Together with the applied voltage, the geometry and dimensions of the fluidic channel determined the electrical parameters of the electroporation. With the optimal design, approximately 75% of the viable CHO cells were transfected after the procedure. We also generalize the guidelines for scaling up these flow-through electroporation devices. We envision that this technique will serve as a generic and low-cost tool for a variety of clinical applications requiring large volume of transfected cells.

Microfluidic electroporation for delivery of small molecules and genes into cells using a common DC power supply

Electroporation is an efficient method of introducing foreign impermeant molecules such as drugs and genes into cells. Conventional electroporation has been based on the application of short electrical pulses (electropulsation). Electropulsation requires specialized equipment and cannot be integrated easily with techniques such as electrophoresis which is based on constant voltage. Here we demonstrate the delivery of small molecules and genes into cells, using a microfluidic electroporation technique based on constant direct current (DC) voltage that we developed earlier. We demonstrate the delivery of two molecules into Chinese hamster ovary (CHO‐K1) cells: a membrane impermeable nucleic acid dye (SYTOX® Green) and a plasmid vector carrying the gene for green fluorescent protein (pEGFP‐C1). Our devices can exert field variations to flowing cells that are analogous to the application of single or multiple pulses by having different geometries. We investigate the effects of the electrical parameters and different geometries of the device on the transfection efficiency and cell viability. Our technique provides a simple solution to electroporation‐based drug and gene delivery by eliminating the need for a pulse generator. We envision that these simple microscale electroporation devices will have the potential to work in parallel on a microchip platform and such technology will allow high‐throughput functional screening of drugs and genes. Biotechnol. Bioeng. 2008;100: 579–586.

A microfluidic cell array with individually addressable culture chambers

Microfluidic arrays of living cells have raised a lot of interests recently due to their potential for high throughput screening of cell-based assays. This report presents a microfluidic cell array with individually addressable chambers controlled by pneumatic valves for cell culture and treatment. There are two modes for the cell array to be operated. In the first mode, different groups of cells are directed into designated chambers for culturing and observation. We demonstrate the delivery and culture of enhanced green fluorescent protein (EGFP) expressing and nonfluorescent Chinese hamster ovary (CHO) cells into specific chambers in the array. In the second mode, the chambers are first seeded with the same cell type and different reagents are delivered to specific chambers for cell treatment. We treat cells in designated chambers with Calcein AM and CellTrace calcein red-orange AM to demonstrate the principle. We envision that this microfluidic cell array technology will pave the way to automated high-throughput screening of biomolecules and drugs based on observing cellular phenotypes and responses.

Membraneless microfluidic microbial fuel cell for rapid detection of electrochemical activity of microorganism

A membraneless microfluidic microbial fuel cell (μMFC) for rapid detection of microorganism electroactivity is demonstrated in this study. Owing to the merit of laminar flow, the proposed μMFC has well-separated anode and cathode without applying proton exchange membrane. The highest open circuit voltages (OCVs) produced by different anodal solutions: fresh medium, inactivated and untreated microflora, were 102, 131, and 246 mV, respectively. These results show that the membraneless μMFC is capable of identifying the electric potential resulting from the imbalanced compositions between two streams (29 mV) and from the electrochemical activity of microflora (115 mV). When samples obtained along a batch cycle of H-type MFC were tested, the membraneless μMFC produced similar OCVs with those from the H-type MFC. In conclusion, the proposed μMFC has comparable abilities in detecting electroactivity with the conventional H-type MFC; moreover, it can distinguish the source of collected electricity.

Microalgae harvesting and subsequent biodiesel conversion.

Chlorella vulgaris ESP-31 containing 22.7% lipid was harvested by coagulation (using chitosan and polyaluminium chloride (PACl) as the coagulants) and centrifugation. The harvested ESP-31 was directly employed as the oil source for biodiesel production via transesterification catalyzed by immobilized Burkholderia lipase and by a synthesized solid catalyst (SrO/SiO2). Both enzymatic and chemical transesterification were significantly inhibited in the presence of PACl, while the immobilized lipase worked well with wet chitosan-coagulated ESP-31, giving a high biodiesel conversion of 97.6% w/w oil, which is at a level comparable to that of biodiesel conversion from centrifugation-harvested microalgae (97.1% w/w oil). The immobilized lipase can be repeatedly used for three cycles without significant loss of its activity. The solid catalyst SrO/SiO2 worked well with water-removed centrifuged ESP-31 with a biodiesel conversion of 80% w/w oil, but the conversion became lower (55.7-61.4% w/w oil) when using water-removed chitosan-coagulated ESP-31 as the oil source.

Rapid and in vivo quantification of cellular lipids in Chlorella vulgaris using near-infrared raman spectrometry.

A rapid and noninvasive quantification method for cellular lipids in Chlorella vulgaris is demonstrated in this study. This method applied near-infrared Raman spectroscopy to monitor the change of signal intensities at 1440 cm(-1) and 2845-3107 cm(-1) along the nitrogen depletion period, and calibration curves relating signal intensity and cellular lipid abundance were established. The calibration curves show that signal intensity at 2845-3107 cm(-1) and cellular lipid abundance were highly correlated. When the calibration curve was applied on the lipid quantification of two unknown samples, the differences between lipid abundances estimated by the calibration curve and measured by gas chromatography were less than 2 wt %. Carotenoids produced a strong and broad peak near 1440 cm(-1), and it weakened the correlation between signal intensity and lipid abundance. The consistency of detection and effects of cellular contents and water on the Raman spectrogram of Chlorella vulgaris were also addressed. The sample pretreatment only involved centrifugation, and the time required for lipid quantification was shortened to less than 1.5 h. The rapid detection has great potential in high-throughput screening of microalgae and also provides valuable information for monitoring the quality of microalgae culture and determining parameters for the mass production of biodiesel from microalgae.

Microfluidic chemical cytometry based on modulation of local field strength.

A simple microfluidic device was demonstrated to analyze intracellular contents from single cells with high throughput based on having different field strengths in geometrically defined sections of a microchannel for electrical lysis and electrophoresis.

Current developments in high‐throughput analysis for microalgae cellular contents

Microalgae have emerged as one of the most promising feedstocks for biofuels and bio‐based chemical production. However, due to the lack of effective tools enabling rapid and high‐throughput analysis of the content of microalgae biomass, the efficiency of screening and identification of microalgae with desired functional components from the natural environment is usually quite low. Moreover, the real‐time monitoring of the production of target components from microalgae is also difficult. Recently, research efforts focusing on overcoming this limitation have started. In this review, the recent development of high‐throughput methods for analyzing microalgae cellular contents is summarized. The future prospects and impacts of these detection methods in microalgae‐related processing and industries are also addressed.

The application of temperature-sensitive paints for surface and fluid temperature measurements in both thermal developing and fully developed regions of a microchannel

This work presents the experimental analysis of heat transfer in a straight polydimethylsiloxane microchannel with cross-sectional width/depth ratio of 8.47 using the temperature-sensitive paint (TSP) technique. The TSP technique is capable of acquiring temperature profiles for both the surface and the fluid with a detailed resolution of 144 µm per pixel through the microchannel under the constant wall temperature condition. The acquired temperature data have been analyzed to study the heat transfer and Nusselt numbers in both thermal developing and fully developed regions. The estimation of thermal entrance length from the experimental results shows good agreement with the empirical equation of the parallel-plate system, while the Nusselt numbers in the fully developed region deviate. This deviation is attributed to the small scale of the channel, which amplifies the effects of the electric double layer and the surface boundary condition. These results demonstrate the great potential of the TSP technique in providing detailed and valuable information for heat transfer investigation inside microdevices.