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Hydrogen sensing is important in many industrial, biomedical, environmental, and energy applications. Realizing a practical, reliable, and inexpensive hydrogen sensor, however, is an ongoing challe...

Hydrogen (H2) sensing is crucial in a wide variety of areas, such as industrial, environmental, energy and biomedical applications. However, engineering a practical, reliable, fast, sensitive and cost-effective hydrogen sensor is a persistent challenge. Here we demonstrate hydrogen sensing using aluminumdoped zinc oxide (AZO) metasurfaces based on optical read-out. The proposed sensing system consists of highly ordered AZO nanotubes (hollow pillars) standing on a SiO2 layer deposited on a Si wafer. Upon exposure to hydrogen gas, the AZO nanotube system shows a wavelength shift in the minimum reflectance by ∼13 nm within 10 minutes for a hydrogen concentration of 4%. These AZO nanotubes can also sense the presence of a low concentration (0.7%) of hydrogen gas within 10 minutes. Their rapid response time even for a low concentration, the possibility of large sensing area fabrication with good precision, and high sensitivity at room temperature make these highly ordered nanotube structures a promising miniaturized H2 gas sensor.

We demonstrate optical hydrogen sensing using metasurfaces based on aluminum-doped zinc oxide (AZO) nanotubes. The sensing system shows 2-13 nm of resonance wavelength shift upon exposure to hydrogen gas of concentration 0.7-4.0 % within 10 minutes.

In this work, we demonstrate a novel low-cost, self-powered paper-based biosensor for glucose monitoring. The device operating mechanism is based on a glucose/oxygen enzymatic fuel cell using an electrochemical energy conversion as a transducing element for glucose monitoring. The self-powered glucose biosensor features (i) a 3D origami paper-based structure for easy system integration onto paper, (ii) an air-cathode on paper for low-cost production and easy operation, and (iii) a screen printed chitosan/glucose oxidase anode for stable current generation as an analytical signal for glucose monitoring. The sensor showed a linear range of output current at 1–5 mM glucose (R2=0.996) with a sensitivity of 0.02 µA mM−1. The advantages offered by such a device, including a low cost, lack of external power sources/sophisticated external transducers, and the capacity to rapidly generate reliable results, are well suited for the clinical and social settings of the developing world.

This work describes the development and operation of a microliter-sized microbial fuel cell-based biosensor for monitoring toxic substances in water. The biosensor features the integration of (i) a three-electrode configuration to provide electrochemical sensing functionality for improving sensitivity and reliability in water quality testing and (ii) an air-bubble trap to prevent all unwanted bubbles from entering the sensing surface for maximizing bacterial growth and their subsequent electron transfer. The miniaturization of the biosensor produced favorable conditions for (i) reducing measurement time with high probability of cell attachment/biofilm formation in the micro-sized chamber and (ii) enhancing the reaction sensitivity with large surface area-to-volume ratio and increased reaction kinetics. When formaldehyde was introduced as a toxic component, the rapid and sensitive current responses were obtained over a concentration range from 0.001% to 0.1% in the biosensor with 0.2 V (versus solid-state thin film Ag/AgCl reference electrode) applied on the anode.

In this paper, we report a multianode paper-based microbial fuel cell (MFC) capable of generating a power density of 28.4 μW/cm 2 . 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/cm 2 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.

Microbial fuel cells (MFCs) are an alternative electricity generating technology and efficient method for removing organic material from wastewater. Their low power densities, however, hinder practical applications. A primary limitation in these systems is the anode. The chemical makeup and surface area of the anode influences bacterial respiration rates and in turn, electricity generation. Some of the highest power densities have been reported using large surface area anodes, but due to variable chemical/physical factors (e.g., solution chemistry, architecture) among these studies, meaningful comparisons are difficult to make. In this work, we compare under identical conditions six micro/nano-structured anodes in micro-sized MFCs (47 μL). The six materials investigated include carbon nanotube (CNT), carbon nanofiber (CNF), gold/poly (ϵ-caprolactone) microfiber (GPM), gold/poly(ϵ-caprolactone) nanofiber (GPN), planar gold (PG), and conventional carbon paper (CP). The MFCs using three dimensional anode structures (CNT, CNF, GPM, and GPN) exhibited lower internal resistances than the macroscopic CP and two-dimensional PG anodes. However, those novel anode materials suffered from major issues such as high activation loss and instability for long-term operation, causing an enduring problem in creating widespread commercial MFC applications. The reported work provides an in-depth understanding of the interplay between micro-/nano-structured anodes and active microbial biofilm, suggesting future directions of those novel anode materials for MFC technologies.

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-?L 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.

We present a microfabricated paper-based microbial fuel cell (MFC) generating a maximum power of 5.5 μW/cm(2). The MFC features (1) a paper-based proton exchange membrane by infiltrating sulfonated sodium polystyrene sulfonate and (2) micro-fabricated paper chambers by patterning hydrophobic barriers of photoresist. Once inoculum and catholyte were added to the MFC, a current of 74 μA was generated immediately. This paper-based MFC has the advantages of ease of use, low production cost, and high portability. The voltage produced was increased by 1.9 × when two MFC devices were stacked in series, while operating lifetime was significantly enhanced in parallel.

In this work, a microfabricated anode based on gold coated poly(ϵ-caprolactone) fiber was developed that outperformed gold microelectrode by a factor of 2.65-fold and even carbon paper by 1.39-fold. This is a result of its ability to three-dimensionally interface with bacterial biofilm, the metabolic “engines” of the microbial fuel cell (MFC). We also examined unavoidable issues as the MFC is significantly reduced in size (e.g. to the microscale); (1) bubble production or movement into the microchamber and (2) high sensitivity to flow rate variations. In fact, intentionally induced bubble generation in the anodic chamber reduced the MFC current density by 33% and the MFC required 4 days to recover its initial performance. Under different flow rates in the anode chamber, the current densities were almost constant, however, the current increased up to 38% with increasing flow rate in the cathode.

We developed a stackable and integrable paper-based microbial fuel cell (MFC) for potentially powering on-chip paper-based devices. Four MFCs were prepared on a T-shaped filter paper which was eventually folded three times to connect these MFCs in series. Each MFC was fabricated by sandwiching multifunctional paper layers for two-chambered fuel cell configuration. One drop of bacteria-containing anolyte into the anodic inlet and another drop of potassium ferricyanide for cathodic reaction flowed through patterned fluidic pathways within the paper matrix, both vertically and horizontally, reaching each of the four MFCs and filling the reservoir of each device. Bacterial respiration then transferred electrons to the anode, which traveled across an external load to the cathode where they combined with protons. The MFC stack connected in series generated a high power density (1.2μW/cm(2)), which is two orders of magnitude higher than the previous report on the paper-based MFC stack. This work will represent the fusion of the art of origami and paper-based MFC technology, which could provide a paradigm shift for the architecture and design of paper-based batteries.

We demonstrate the use of a paper-based sensing platform for rapid and high-throughput characterization of microbial electricity-generating capabilities. For the first time, a 48-well microbial fuel cell (MFC) array was fabricated on paper substrates, providing 48 high-throughput measurements and highly comparable performance characteristics in a reliable manner. Spatially distinct 48 wells of the sensor array were prepared by patterning 48 hydrophilic reservoirs in paper with hydrophobic wax boundaries. The paper-based platform exploited the ability of paper to quickly wick fluid and promote bacterial attachment to the gold anode pads, resulting in an instant current generation upon loading of bacterial inoculum and catholyte. This paper-based 48-well MFC array does not require external pumps/tubings and represents the most rapid and the highest throughput test platform for electrogenic bacterial screening.

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.

We report a nine-well MEMS-based parallel analyses platform for testing electricity generation capacity of eight microbial consortia, which provides high throughput characteristics for bacterial electrogenic screening. The presented device features independent fluidic access to each analysis unit allowing for long term analysis ability without contamination from chamber to chamber during operation. The device contains vertically stacked 57μL anode/cathode chambers separated by a proton exchange membrane (PEM) and each device component is thermally assembled without mechanical supporting frames/bolts/nuts. This device will create a compact screening system individually addressable for identification and characterization of electrochemically active microbes.

Integration of electrochemical analytical functionality into a micro-sized microbial fuel cell is demonstrated. Screen-printed carbon ink based working (anode) and counter (cathode) electrodes and Ag/AgCl ink based reference electrode were deployed for sensing. Using such three-electrode configuration, in-situ cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were successfully performed to study the behavior of microbial electron transfer at the anode and to evaluate electrochemical properties of the MFC. In this work, coupling of electrochemical studies to the MFC platform has provided valuable information leading to a quantitative understanding of bacterial redox potential mass transport and the electrode/bacteria electron transfer kinetics.

We report a microfabricated paper-based bacteria-powered battery generating 10 μW/cm 2 . Only four batteries connected in series provided desired values of current and potential to power an LED for more than 30 minutes without power management interface circuits. The battery features (i) a low-cost paper-based proton exchange membrane directly patterned on commercially available parchment paper with laser treatment and (ii) paper reservoirs for holding the anolyte and the catholyte for extended period of time. Since sewage or soiled water in a puddle can become an excellent source for extracting bioelectricity through bacterial metabolism, this paper-based bacteria-powered battery is expected to be a simple, low-cost, and easy-to-use power source for single-use paper-based diagnostic devices in resource-limited settings.

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/cm 2 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.

We report a multi-anode paper-based microbial fuel cell (MFC) capable of generating a power density of 28.4 μW/cm2. This MFC features (i) flexible multilayered carbon anodes for bacterial attachment and (ii) paper reservoirs for holding the anolyte and catholyte for an extended period of time. By using the multi-anode MFC, the power and current densities increased by 5x and 3x, respectively, compared to 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.

We report a paper-based microbial fuel cell (MFC) generating a maximum power of 5.5 μW/cm2. The MFC features (1) a paper-based proton exchange membrane by infiltrating sulfonated sodium polystyrene sulfonate and (2) micro-fabricated paper chambers by patterning hydrophobic barriers of photoresist. Once a sample was added to the device, a current of 74 μA generated without any startup time. This paper-based MFC has the advantages of ease of use, low production cost, and high portability. The voltage produced was increased by 1.9× when two MFC devices were linked in series while operating lifetime was significantly enhanced in parallel.

Due to an increased concern about the global energy crisis and environmental pollution, microbial fuel cells (MFCs) have been a major focus for renewable energy production. To date, however, a surprisingly small number of bacterial strains and their optimal growth conditions have been investigated for use in MFCs, revealing a crucial lack of fundamental knowledge as to which bacteria species or consortia may be best suited for generating power in MFCs. This lack of knowledge is due to the fact that current screening methods are depending on larger scale two-bottle MFCs that require long start-up times, as well as the inability of conventional MFC arrays to generate electricity in a reliable, robust, and reproducible manner. In particular, the influence of light on the bacterial growth conditions and their power generation has not been fully reported because conventional MFC's opaque device/anode configuration leads to inefficient light penetration. This paper presents a miniaturized high-throughput parallel analyses platform not only for the screening/characterization of the electrochemical activities of electrogenic bacteria but also for investigation of the effect of light on bioelectricity generated from eight different microbial consortia in anode or cathode compartment; wild-type Shewanella oneidensis MR-1, Synechocystis sp. PCC 6803, wild-type Pseudomonas aeruginosa PAO1, and isogenic nirS, lasl, bdlA, and rpoS mutants, respectively. The array consists of nine MFC units with (i) transparent thin gold anode on PMMA layers for efficient light penetration and (ii) independent microfluidic accesses allowing for long term analysis ability without contamination from chamber to chamber during operation. Each MFC unit contains vertically stacked 57 μl anode/cathode chambers separated by a proton exchange membrane. S. oneidensis displayed the highest current generation among all the consortia, 4-fold higher than that of wild-type P. aeruginosa PAO1. However, all the other mutants produced significantly low current outputs. Current production by Synechocystis sp. PCC 6803 demonstrated a positive response upon illumination and a subsequent decrease of output in the dark while other MFC units showed negligible light responses.

Application of micro-scale microbial fuel cells (MFCs) to power electronics is limited due to the high internal resistances associated with membranes. Laminar flow MFCs (LFMFCs) provide an advantage over conventional designs because the anode and the cathode are naturally separated due to the laminar flow regime that develops within the reactor, eliminating the need for membranes. However, our ability to fully harness the potential of LFMFC technology lags from a lack of in-depth understanding of anode/cathode analyte mixing and fundamental factors that maximize LFMFC's power-generating capabilities. We, therefore, investigated the anode colonization and respiration of the known exoelectrogenic bacterium, Geobacter sulfurreducens, in a micro-scale LFMFC. Current production was dependent on the location of the anode relative to the influent in continuous-flow operation, with the highest current density of 6.5 μA/cm2 recorded closest to the influent. Lateral diffusion of anode/cathode analytes, in addition to upstream substrate consumption, likely resulted in the observed differences in current production. As current increased, the number of bacterial cells on the anode measured using simultaneous microscopic observation, also increased. Although the current density obtained here was substantially lower than other micro-sized MFCs, these findings show that micro-scale LFMFCs adapted to microscopic observation can provide a unique tool for better understanding real-time anode colonization and overall reactor performance.