|Fig. 1: Bacillus Spores. (Source: Wikimedia Commons)|
The purpose of this publication is to spread the work of Ozgur Sahin and his team at Columbia University on a rather new concept of converting energy. Sahin and team have created a technology that, when placed above a water source, uses the evaporation from the water to produce energy. Sahin and his team at Columbia have only used it in small scale to power linear locomotion and power light sources. This energy transfer takes place through pores in a particular bacterium that function like muscles and produce energy. Fig. 1 to the right shows an image of these bacteria spores. This process will be explained later on. If this process can be harnessed and manipulated in the right way by maximizing pore capacity it could be turned into a very productive energy source. Mainly, this technology would be advantageous in powering technologies such as sensors and technologies that function in the natural environment.
Bacillus spores are dormant cells that can be found in plants and other organisms that are water responsive structures. These dormant cells can withstand harsh environments while containing their functionality of responding to changes in humidity levels. According to Sahin and his team's research, as the humidity increases the spores increase in diameter, very similar to the flexion of ones muscle in the body. This flexion and extension due to the humidity change produces work. A large amount of these spores are dried and placed on silicon microcantilevers and latex rubber sheets that curve with the "strain" of the spores as humidity levels change. This curving of the latex is used in combination with a hygrovoltaic generator to gather the energy current. Sahin and his team have used this current to propel light locomotion and small windmill like structures. 
Throughout the numerous tests that the Columbia University team ran, the main challenge is identifying the specific pores that will produce the greatest energy output. Different types of spores have different sizes, number of layers, and distance to the cortex. All these factors affect the amount of strain or stretching the spores can handle. The larger the strain leads to the larger energy current. The next challenge for Sahin and his team is to continue to develop more advanced technology to increase spore capacity on the latex sheets to increate the output current to be able to apply this technology to larger machines. 
© Greg Taboada. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 X. Chen et al., "Bacillus Spores as Building Blocks for Stimuli-Responsive Materials and Nanogenerators," Nat. Nanotechnol. 9, 137 (2014).
 X. Chen et al., "Scaling up Nanoscale Water-driven Energy Conversion into Evaporation-Driven Engines and Generators," Nature Communications 6, 73346 (2015).