Biofuel cell as a power source for electronic contact lenses Magnus Falk a,1 , Viktor Andoralov a,1 , Zoltan Blum a , Javier Sotres a , Dmitry B. Suyatin b , Tautgirdas Ruzgas a , Thomas Arnebrant a , Sergey Shleev a,c,n a Biomedical Science, Health & Society, Malm¨ o University, 205 06 Malm¨ o, Sweden b Division of Solid State Physics, The Nanometer Structure Consortium, and Neuronano Research Center, Lund University, 221 00 Lund, Sweden c The Laboratory of Chemical Enzymology, A.N. Bach Institute of Biochemistry, 119 071 Moscow, Russia article info Article history: Received 14 February 2012 Received in revised form 16 April 2012 Accepted 17 April 2012 Available online 4 May 2012 Keywords: Enzymatic fuel cell Direct electron transfer Human lachrymal liquid Electronic contact lens abstract Here we present unequivocal experimental proof that microscale cofactor- and membrane-less, direct electron transfer based enzymatic fuel cells do produce significant amounts of electrical energy in human lachrymal liquid (tears). 100 mm diameter gold wires, covered with 17 nm gold nanoparticles, were used to fashion three-dimensional nanostructured microelectrodes, which were biomodified with Corynascus thermophilus cellobiose dehydrogenase and Myrothecium verrucaria bilirubin oxidase as anodic and cathodic bioelements, respectively. The following characteristics of miniature glucose/ oxygen biodevices operating in human tears were registered: 0.57 V open-circuit voltage, about 1 mW cm 2 maximum power density at a cell voltage of 0.5 V, and more than 20 h operational half- life. Theoretical calculations regarding the maximum recoverable electrical energy can be extracted from the biofuel and the biooxidant, glucose and molecular oxygen, each readily available in human lachrymal liquid, fully support our belief that biofuel cells can be used as electrical power sources for so called smart contact lenses. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Researchers presently working in the field of biofuel cells (BFCs) fully appreciate that basic characteristics of conventional fuel cells (FCs), widely used as electrical power sources in different applica- tions nowadays, are superior compared to even recently fabricated, advanced biodevices that draw on the latest bionanotechnological achievements (Gao et al., 2011; Miyake et al., 2011; Zebda et al., 2011). Nonetheless, it is a widely held notion that particular BFCs could find their own niches in various practical applications. Owing to a number of advantageous properties, e.g., adequate stability, simplicity, low cost, and bioremediation, microbial FCs might be used as green sources of electrical power for miscellaneous inanimate entities (Bath, 1995; Lovley, 2008). Contrary to microbial biodevices, minute discrete enzyme based FCs might be suitable electrical power sources for self-contained implantable electronic devices (Barton et al., 2004; Heller, 2004). However, it should be emphasized that the actual in vivo performance of enzymatic FCs already tested (e.g., in Ref. (Cinquin et al., 2010)) is untenable; based not only on the intrinsic properties of BFCs, i.e., operating voltage, power density, and operational stability, which per se can be significantly improved using bionanotechnological approaches, but also on very serious complications developing as a conse- quence of implantation, i.e., immunoresponse, incapsulation, and much more (Cinquin et al., 2010). One promising biomedical application of BFCs, which has not been realized yet, is the employment of these devices in non- invasive (extra vivo or ex vivo) contact situations, where most of the in vivo shortcomings are non-issues. The term ex vivo will henceforth substitute the previously used illogical term ‘‘semi- implantable’’ regarding attachable, adhesive, floating devices operating in saliva, tears, and sweat, which somehow lies in between in vivo and in vitro situations. Among the many devices operating in contact modes, e.g., electronic skin patches (Duun et al., 2010), one can easily identify exciting devices, viz. ‘‘smart’’ electronic contact lenses (SECLs), with prominent application potentials for e.g., human supervision (Yao et al., 2011), extra vivo biomedical sensing (Chu et al., 2011; Yao et al., 2011), etc. Significant conflicts between the main parameters (voltage and power required vs. ultimate miniaturization) of the major parts of self-contained wireless devices in general, and SECLs in particular (Fig. 1), e.g., the (bio)sensor, light-emitting diodes or liquid crystal based displays, the transmitter/operating system, the electrical power source, have so far prevented its practical realization. One of the largest components in current self-con- tained devices is the power source. Obviously, in the case of thin Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/bios Biosensors and Bioelectronics 0956-5663/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.bios.2012.04.030 n Corresponding author at: Malm ¨ o University, Biomedical Science, Faculty of Health and Society, Jan Waldenstr ¨ oms gata, 205 06 Malm ¨ o, Sweden. Tel.: þ46 40 6657414; fax: þ46 40 665 8100. E-mail address: sergey.shleev@mah.se (S. Shleev). 1 Equally contributed to the present work. Biosensors and Bioelectronics 37 (2012) 38–45