Nature Communications 2, Article number: 448 (2011); Published: 23 August 2011; Updated: 7 February 2012

This article was published without any declaration of competing financial interests. A revised competing financial interests statement is provided below:

The authors declare competing financial interests. T.K. and J.A.T. are employees with InStep NanoPower, LLC. T.K. is a company President and J.A.T. is a company Vice President.