Hankeun Lee

A Multianode Paper-Based Microbial Fuel Cell: A Potential Power Source for Disposable Biosensors

In this paper, we report a multianode paper-based microbial fuel cell (MFC) capable of generating a power density of 28.4 μW/cm2. This MFC features: 1) flexible multilayered carbon cloth anodes for bacterial attachment and 2) paper reservoirs for holding the anolyte and catholyte for an extended period of time. The hydrophobic barriers in the anodes and paper-based reservoirs were patterned by impregnating and selectively polymerizing photoresist through UV lithography. Upon inoculum/catholyte introduction, a current of 211 μA/cm2 was immediately generated. By using the multianode MFC, the power and current densities increased by 5× and 3×, respectively, compared with a single anode one. The paper-based MFC is expected to be a simple and easy-to-use power source for single-use diagnostic biosensors because even sewage or soiled water in a puddle can become an excellent source for operating MFCs and harvesting electricity through bacterial metabolism.

A microsized microbial fuel cell based biosensor for fast and sensitive detection of toxic substances in water

We report a microliter-sized (140 μL) microbial fuel cell (MFC)-based biosensor integrated with a three-electrode configuration and an air-bubble trap, in which microorganisms act as the sensor for toxic substances in water. The small-scale MFC biosensor produced favorable conditions for (i) reducing measurement time by increasing the probability of cell attachment and biofilm formation in the micro-sized chamber and (ii) enhancing sensitivity and reliability by providing a stable anodic potential and preventing air bubbles on the sensing surface. Using formaldehyde as a toxic component, the rapid current responses were obtained over a concentration range from 0.001% to 0.1% in a single chambered MFC biosensor with 0.2 V (versus Ag/AgCl reference electrode) applied on the anode.

A Microsized Microbial Solar Cell: A demonstration of photosynthetic bacterial electrogenic capabilities.

This article focuses on a microsized microbial solar cell (MSC) that can produce sustainable energy through photosynthetic reactions of cyanobacteria Synechocystis PCC 6803 in the anode. The MSC has 57-μL anode/cathode chambers defined by laser-machined poly(methyl methacrylate) (PMMA) substrates. We obtained a maximum power density of 7.09 nW/cm2, which is 170 times more power than previously reported microelectromechanical system (MEMS) MSCs. The importance of the light intensity was demonstrated by the higher values of generated current during the day than at night, indicating light-dependent photosynthetic processes. Considering that sunlight offers an unlimited source of energy, the development of self-sustainable MSCs that rely on light as an energy source will become an increasingly important area of research in the future. In accordance with the MSC, we developed a photosynthetic cathode-based microbial fuel cell (MFC), showing that the use of cyanobacteria can be useful as well as efficient and sustainable catalysts for the cathode since they act as oxygenators.

A paper-based cantilever array sensor: Monitoring volatile organic compounds with naked eye

Volatile organic compound (VOC) detection is critical for controlling industrial and commercial emissions, environmental monitoring, and public health. Simple, portable, rapid and low-cost VOC sensing platforms offer the benefits of on-site and real-time monitoring anytime and anywhere. The best and most practically useful approaches to monitoring would include equipment-free and power-free detection by the naked eye. In this work, we created a novel, paper-based cantilever sensor array that allows simple and rapid naked-eye VOC detection without the need for power, electronics or readout interface/equipment. This simple VOC detection method was achieved using (i) low-cost paper materials as a substrate and (ii) swellable thin polymers adhered to the paper. Upon exposure to VOCs, the polymer swelling adhered to the paper-based cantilever, inducing mechanical deflection that generated a distinctive composite pattern of the deflection angles for a specific VOC. The angle is directly measured by the naked eye on a 3-D protractor printed on a paper facing the cantilevers. The generated angle patterns are subjected to statistical algorithms (linear discriminant analysis (LDA)) to classify each VOC sample and selectively detect a VOC. We classified four VOC samples with 100% accuracy using LDA.

An origami paper-based bacteria-powered battery with an air-cathod

In this work, we created a stackable, 3-D, paper-based, bacteria-powered battery for potentially powering on-chip paper-based biosensors. The battery generated power from microbial respiration with one drop of bacteria-containing liquid. An air-cathode was also created on paper with activated carbon on the Nickel electrode that was sprayed on the paper. By applying paper-folding techniques, the four on-chip batteries were connected in series to obtain a high operating voltage (0.1V) under a 470kΩ external resistor. Shewanella oneidensis were loaded on to the folded battery stack, through which the bacterial cells were transported into each battery. For operation, the battery stack was unfolded to expose all air-cathodes to the air, thereby maximizing their cathodic reactions.

A biological solar panel

We report a prototype scalable and stackable biological solar panel by installing miniature biological solar cells in an array format. Nine small-scale biological solar cells were integrated in a panel along with a common feed microfluidic channel. The biological solar panel continuously generated electricity from microbial photosynthetic and respiratory activities under day-night cycles. Requiring only sunlight, water, and carbon dioxide to operate, the biological solar panel offers advantages over potentially competing sustainable power sources such as microbial fuel cell stacks or photovoltaic panels because the photosynthetic microorganisms used here a) do not require an organic fuel, and b) are capable of producing power both during the day and at night.

A micro-sized microbial solar cell

We report a micro-sized microbial solar cell (MSC) that can produce sustainable energy through photosynthetic reactions of cyanobacteria, Synechocystis PCC 6803 in the anode. The MSC has 57-μL anode/cathode chambers defined by laser-machined poly(methyl methacrylate) (PMMA) substrates. We obtained a maximum power density of 7.09 nW/cm2 which is one hundred seventy times more power than previously reported MEMS MSCs. The importance of the light intensity was demonstrated by the higher values of generated current during daytimes than those through the nights, indicating light-dependent photosynthetic processes. Considering that sunlight offers an unlimited source of energy, development of self-sustainable MSCs that rely on light as an energy source will become an increasingly important area of research in the future. In accordance with the MSC, we developed a photosynthetic cathode-based microbial fuel cell (MFC) showing that the use of cyanobacteria can be useful as well as efficient and sustainable catalysts for the cathode since they act as oxygenators.