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For Popeye, he's "strong to the finish, ‘cause [he] eats his spinach," and many nutritionists would agree, as the vegetable contains vitamin A, vitamin C, vitamin K, iron, calcium, and folic acid. Another nutrient in spinach, nitrate, has even been found to increase fast-twitch muscle strength in mice by acting on two proteins, CASQ1 and DHPR, involved in calcium-dependent contraction.1 Despite this trial's results being observed after a week of nitrate consumption, luckily for pugnacious Popeye, a can of spinach is always handy whenever he needs an instant boost.
Recently, a team of researchers from Vanderbilt University have taken a page from the Popeye comic book by incorporating a photosynthetic protein of spinach into a biohybrid solar cell.2 The plant protein, Photosystem 1 (PS1), can convert light into electrochemical energy and maintain this function after its extraction.3 As reported in Advanced Materials, the team of chemists and engineers applied these qualities by combining the material typically used for solar cells, silicon, with a PS1 solution to make a unique device, one that produces nearly two and a half times more current than any prior biohybrid cell.
To explain this higher performance, it is helpful to have some background on how the PS1 protein works. Each plant PS1 protein operates by absorbing photons from sunlight and using them to transfer electrons across a thylakoid membrane to generate energy. In natural conditions, PS1 proteins, their thylakoid membranes, and the electrical gradients the membranes create are all aligned in the same direction, such that high levels of energy are generated. In this experiment's biohybrid cells, however, the PS1 proteins are randomly oriented, as after they were extracted from the spinach, they were mixed into a solution and poured over wafers of silicon. In other experiments with metal substrates, these random orientations caused the various currents to cancel each other out.
For these PS1-silicon cells, though, the team "doped" the silicon wafers by implanting positive electrically-charged atoms in them before pouring the PS1 solution over them. This doping gives the wafers an overall positive charge and promotes a more standardized electron transfer that helps compensate for the random orientation of the PS1 proteins. To give a comparison, while a PS1-gold electrode device was able to produce a charge of 0.35 microamps/cm2, the p-doped PS1-silicon cell generated a charge of 875 microamps/cm2, representing a 2,500 fold improvement.
Considering that the materials for the biohybrid cell are inexpensive and readily available, this high efficiency is energizing in itself. More research on PS1-silicon cells is necessary before they could become commercially available, especially regarding PS1 protein degradation, but this alternate solar design has some serious potential. In the 1951 cartoon "Double-Cross Country Race," Popeye hilariously saves a sabotaged car by feeding it spinach, going on to win a cross-country race with the subsequent surge of energy. Apparently, outside of the funny papers, spinach fuel now is no laughing matter.
Image credit: Image of comic book cover with Popeye growing spinach is from Flickr's Felix_Nine.
1. Hernández, A., Schiffer, T. A., Ivarsson, N., Cheng A. J., Bruton, J. D., Lundberg, J. O., Weitzberg, E., & Westerblad H. (2012). Dietary nitrate increases tetanic [Ca2+]i and contractile force in mouse fast-twitch muscle. The Journal of Physiology, 590, 3575-3583 PMID: 22687611
2. Leblanc, G., Chen, G., Gizzie, E. A., Jennings, G. K. & Cliffel, D. E. (2012). Enhanced photocurrents of Photosystem I films on p-doped silicon. Advanced Materials. PMID: 22945835
3. Salisbury, D. "Spinach Power Gets Major Boost." Research News @ Vanderbilt. September 4, 2012.
