Team:NYMU-Taipei/Design

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  • Experiment
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  • Functional
    Prototype
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Functional prototype

This year we decided to build a soil-based microbial fuel cell(SMFC) wireless sensor that can generate electricity whenever the genetically engineered Shewanella oneidensis MR-1 JG700. These are the components to build a SMFC wireless sensor

Components

Graphite fiber electrode

For our device to detect salicylic acid, we need to inoculate Shewanella on the anode. In our work, we ordered cathode and anode from Keego Technologies LLC, Stanford, USA. Soil was patted down in MFC up to 1 cm to make a smooth surface and anode was placed on the top of the soil, finally soil sample was added. The cathode was placed on the top of the soil. The graphite fiber electrode allows the bacteria to make more contact with the electrode so that the bacteria can transfer much more electrons to the electrode than graphite electrode. We use titanium wire instead of the copper one since the corrosion resistance of the former is better than the latter in soil and will do less harm to the environment.

External Power source

To deploy our device for a long time period, the wireless sensor network requires an autonomous electrical source in the wild that can recharge and store energy for extended periods of time. We used a solar portable charger to charge to power the wireless sensor. We would like to give a special thanks to Professor You-Yin Chen, a Lecturer in the Department of Biomedical Engineering, for his guidance. We integrated the battery into our device.

Potentiostat

The potentiostat is used to provide and maintain a voltage potential between the working electrode(WE) and reference electrode(RE) of the SMFC. It also interfaces with the counting electrode to provide a measurement for its current flow. This measurement is recorded and sent to a phone app. The working electrode, reference electrode, and counter electrode are made of Au, Ag/AgCl, and Pt respectively. We powered this system by a 3.3V battery. We designed this system with operational amplifiers (OPA), due to their robustness in different operating conditions. We would like to thanks Professor You-Yin Chen, a Lecturer in the Department of Biomedical Engineering, for helping us designing the potentiostat. The design is shown as the diagram bellow

Microcontroller

The measurement from the potentiostat is fed into an Media Tek LinkIt ONE. The analogue is converted using an analog-to-digital converter and stored in the device. Using serial communications, the measurement is transmitted via a USB interface to an Android device. We sample this measurement at 125 kHz, constantly sending new information serially