Biopower-on-Skin: Electricity generation from sweat-eating bacteria for self-powered E-Skins

Electronic skins or ‘e-skins’ have recently emerged as a novel platform for electronics, taking on more important roles in health diagnostics, therapeutics, and monitoring. Stand-alone and self-sustained e-skins are essential to providing reliable, effective and sometimes life-saving functions. A stable power supply is the most critical factor in developing practical e-skins because their performance depends significantly on power availability. A realistic and accessible power source is urgently needed for the next generation of smart, stand-alone, always-on e-skin systems. This is by no means a simple challenge because intimately integrating technologically advanced e-skins with human skin requires generating power from an extremely complicated, harsh environment. Skin is cool, dry, acidic and has few potential energy sources. In this work, we create the ability to generate an innovative, practical, and longstanding power from human sweat, which is one of the few available energy resources on skin. We use the metabolisms of sweat-eating bacteria that exist on human skin, Staphylococcus epidermidis, Staphylococcus capitis, and Micrococcus luteus. We also test a microorganism, Nitrosomonas europaea, that oxidizes the ammonia in sweat, but is not usually found on the skin. Bioelectrogenesis from all the bacterial species were observed at levels comparable to that of a well-known wild-type electrogenic bacteria, Shewanella oneidensis MR1, which inhabits the natural environment. A biobattery, or a microbial fuel cell, that uses bacteria as a biocatalyst, transforms the chemical energy of sweat into electrical power through bacterial metabolism. The skin-mountable biobattery is pre-inoculated with the sweat-eating bacteria and operates with human sweat, delivered by an integrated battery-free skin-interfaced microfluidic system. Given that the total non-human microbial cells inhabiting in and on our bodies outnumber the human cells by at least a factor of 10, the direct use of the microbial cells to produce power is conceivable for e-skins. The significance of this work stems from the demand for self-sustainable and stand-alone e-skin systems for healthcare, security, fitness, and environmental monitoring applications.