Epidermal biofuel cells: energy harvesting from human perspiration.

The healthcare industry has recently experienced a major paradigm shift towards wearable biomedical devices. Such devices have the ability to monitor vital physiological parameters, such as heart rate or blood pressure. Particular recent attention has been directed towards skin-worn electronic devices fabricated by novel hybrid techniques for the measurement of these vital signs. Despite dramatic technological advances, further progress in the arena of on-body biomedical devices has been hindered by the lack of effective wearable power sources able to scavenge sufficient energy from the wearer. Major efforts have thus been directed towards the identification of a suitable wearable power source that offers conformal integration with the wearer s body. This activity has resulted in the development of flexible thin-film batteries, piezoelectric nanogenerators, wearable solar cells, mircosupercapacitors, and endocochlear-potential-based biobatteries. Nevertheless, new body-worn conformal power sources able to extract biochemical energy from the wearer s body (and his/her epidermis, in particular) are still highly desired. Herein we demonstrate the ability to generate substantial levels of electrical power from human perspiration in a noninvasive and continuous fashion through the use of epidermal biofuel cells based on temporary transfer tattoos (tBFCs). Enzymatic BFCs have attracted considerable interest owing to their ability to generate power from the bioelectrocatalytic reaction of common chemicals and metabolites, such as glucose and alcohol, under physiological conditions. Recent efforts resulted in implantable glucose BFCs that can generate significant power densities in small animals, such as snails, insects, and rats. However, there are no reports on harvesting the chemical energy from a human in connection with the rapidly developing field of wearable electronics. The successful development of non-invasive tBFCs requires the judicious integration of new manufacturing processes and advanced surface functionalization for efficient power generation from lactate present in the wearer s perspiration. The development of the tBFC builds on our recent introduction of epidermal electrochemical sensors. The two electrode constituents of the new wearable tBFC were designed in the shape of “UC” (acronym for “University of California”; Figure 1; see Figure S1 in the Supporting