Freeze-drying extends paper biobatteries’ shelf-life

Paper-based batteries fueled by bacteria have the potential to be a low-cost power source for biosensors that diagnose diseases. But such batteries’ shortcomings include limited shelf lives of a couple of days. Seokheun (Sean) Choi, an electrical engineer at Binghamton University, has extended the shelf life of paper-based biobatteries by freeze-drying electric bacteria in paper and then rehydrating them to turn the batteries on. He presented the work Sunday at the American Chemical Society national meeting in Boston in a symposium in the Division of Analytical Chemistry.

Choi made biobatteries by embedding electric bacteria, so-called exoelectrogens, in pores in paper. As a byproduct of their respiration, these bacteria export electrons that can be harvested and stored in batteries. Choi engineered the paper to be conductive by adding a water-dispersed conducting polymer mixture, which improved performance relative to previous biobatteries by creating a conductive anodic reservoir that allowed electrons to be harvested from more of the bacteria. Previously, electrons could be harvested only from bacteria near the anode. In previous work, he used multiple paper layers to make biobatteries. In this work he fabricated multiple battery cells on a single sheet of paper and folded the paper to yield seven battery cells connected in series.

For long-term storage, Choi freeze-dried the batteries after adding the bacteria. But he didn’t just freeze-dry the bacteria, which has been done before. He also included a pouch of cell-culture medium, which can be released by manually squeezing. The medium rehydrated the cells and provided them an energy source. He was able to store the batteries for four weeks. He didn’t optimize the storage conditions, so he doesn’t know the maximum storage time.

Each seven-cell battery pack produced about 88 microwatts. Three of the seven-cell battery packs produced enough power to run a red light-emitting diode, and two of the battery packs powered an electric calculator.

George M. Whitesides, a Harvard University pioneer in paper-based devices, was impressed with the power density Choi achieved with the paper batteries. He also pointed out that under the right conditions the cellulose in the paper could potentially serve as a food source for bacteria in addition to serving as a scaffold.