Self-Powered Environmental Monitoring Using Insect-Mountable Biofuel Cell
Authors: Shoji Kan , Akiyama Yoshitake , Nakamura Nobuhumi , Ohno Hiroyuki , Morishima Keisuke 
Published: February 2020

This paper reports the first demonstration of a self-powered environmental monitoring robot which backpacked a biofuel cell (BFC) and a micro wireless sensor module on an insect. Electric power was generated from blood sugar in its hemolymph by the BFC and temperature and humidity was monitored by the wireless sensor module.
Insect cyborgs, which are micro robots controlled by electric stimulation for their brain and muscles, are desired to be utilized as a search robot and an environmental monitoring robot. However, coin batteries which are currently used for power sources of insect cyborgs have issues for practical use of insect cyborgs. They not only interfere with insect’s locomotion because of their size and weight but also they have to be recharged or replaced to drive an integrated circuit for a long time. Our group has already reported a BFC using trehalose found in insect hemolymph and succeeded in driving some IC devices. In this paper, we proposed an insect-mountable BFC (imBFC) and developed the self-powered and autonomous distribute sensor robot by mounting the BFC and the wireless sensor module onto insect.
The imBFC consisted of two chambers (top: length, 18 mm; width, 9mm; depth, 0.5 mm, bottom: length, 18 mm; width, 9mm; depth, 1 mm) separated by dialysis membrane (MWCO: 500-1000) and enzymatic electrodes (surface area, 118 mm2). The chambers were fabricated with a 3D printer (RVS-S1, Real Vision Systems Inc.) and a 500 nm thick parylene layer was deposited on the surface of the chambers. Trehalose molecules found in insect hemolymph are curried to the chamber connected to insects by diffusion and the trehalose molecules are decomposed to glucose molecules by trehalase. Then, the glucose molecules are oxidized by glucose dehydrogenase (GDH) immobilized on an anode and oxygen is reduced by bilirubin oxidase (BOD) immobilized on a cathode. As a result of these processes, electricity is generated. A maximum power output of 333 µW (285 µW/cm2) was obtained at 0.5 V in the imBFC. Because electrodes were not implanted in the insect but mounted on the insect, larger electrodes could be used in the imBFC and the maximum power output reached 333 µW.
Then, we developed the micro wireless sensor module and demonstrated to monitor environmental conditions by mounting the sensor and the BFC on the insect. The wireless sensor module consisted of a power circuit (ADP5090, Analog Devices Inc.) which boosted the voltage from around 400 mV to 2.5 V, a wireless transmitter (carrier frequency, 315 MHz), a temperature and humidity sensor (SHT20, Sensirion AG) and a microcomputer (PIC16LF1824, Microchip Technology Inc.). The voltage of the imBFC was boosted to 2.5 V by the power circuit and charged to tantalum capacitors (total capacity, 2200 µF). First, the capacitor was charged until the start-up voltage of the wireless sensor module and the microcomputer. Then, the microcomputer and the sensor were driven and temperature and humidity were measured. These processes were repeated until the power output of the imBFC was reduced bellow the energy consumption of the wireless sensor device. The size and weight of the wireless sensor are 10 mm × 10 mm × 8 mm and 1.3 g, respectively. The insect, which backpacked the BFC and the wireless sensor module, walked autonomously and first temperature and humidity data were transmitted about 26 min after the imBFC was connected to the wireless sensor module. Then, the temperature and humidity data were transmitted 3 times for 8 min. We succeeded in the first demonstration of the self-powered environmental monitoring robot which generates electric power from its body fluid and activates the wireless sensor by the electric power.
This study investigated the self-powered bio-hybrid robots which generate electric power from their body fluid and monitor the environmental conditions by the wireless sensor backpacked insect. The maximum power output of the imBFC reached 333 µW at 0.5 V. To the best of our knowledge, our imBFC has the highest performance of any living battery. Furthermore, we succeeded in monitoring the environmental conditions by using the insect which was mounted the BFC and the micro wireless sensor module. These results indicate that self-powered sensor robots have potential to be applied an autonomous distributed sensor network for environmental monitoring. Furthermore, the power generation mechanism of the imBFC can be applied to all living organisms because all living organisms utilize sugar as energy for their activity. In future work, the BFC might be utilized as a battery of biomedical devices, sensors and robots implanted into human beings.

Figure 1