Coating of fuel cells using carbohydrate solutions

The current popular technique of preservation using cryogenic storage has several disadvantages especially in terms of the specialized equipment required. Preservation at ambient temperatures would eliminate the need for cryogenic equipment and the associated costs. Preservation of Geobacter Sulfurreducens (the bacterial fuel cell) at ambient temperatures would be particularly useful given its potential applications in technology. This has led to preliminary experiments for the preservation of the Geobacter Sulfurreducens in carbohydrate-based glasses using inositol, trehalose and sucrose. Geobacter was suspended in various carbohydrate solutions prepared from a stock solution of 4% D ₂O in PBS and deposited on CaF₂ slides in the form of small (400nl) droplets and dried isothermally at ambient temperatures. FTIR (Fourier Transform Infrared Spectroscopy) analysis of droplets containing the carbohydrate solutions and the Geobacter were performed to determine the desiccation characteristics of the carbohydrate solutions, their coating efficiency and the desiccation induced damage in Geobacter as a function of desiccation conditions. D ₂O in the experimental solutions provided a unique peak around 2500 cm^-1 in the IR spectra, which is used to quantify the water content of the sample. Optical analysis of the desiccated solutions showed heterogeneous conditions within the drying droplets. Comparison of the IR spectra at the center and the periphery of the droplets showed significant differences. This is thought to be a result of the bacteria clumping in the center regions and rejecting the solutes in the carbohydrate solution toward the circumference of the droplet. It was also observed that the peak magnitudes of the trehalose, sucrose and inositol were comparatively larger as compared to the amide-I peak (showing the bacteria concentration) at the circumference than at the center. This is in agreement with the optical observat- - ions showing glassy areas forming at the circumference during drying for the solutions containing sucrose and trehalose. These initial experiments demonstrated the heterogeneities occuring in sessile droplets during desiccation. Research is under way to develop methods that will enable homogeneous desiccation and vitrification of the biopreservation solutions coating the Geobacter. Additionally, mechanisms of desiccation-induced damage in Geobacter, the protection mechanisms of carbohydrates and the thermodynamics of the carbohydrate-based solutions are examined