Читать книгу Biofuel Cells - Группа авторов - Страница 28

One of the great limitations of enzymatic biofuel cells is the low energy output compared to the well-established inorganic counterparts. However, together with their mild operation conditions, this has made them a suitable candidate as an implantable power source [21].

Besides the obvious applications in energy conversion, enzymatic biofuel cells have been proposed as so called “self-powered” biosensors. Katz’s original idea was to use the open circuit potential as an indicator of the concentration of the fuel (glucose or lactate) [132]. However, subsequent developments used an amperometric approach, in which a constant resistance would be connected to the fuel cell and the measured current across it taken as analytical signal [146]. It must be noted, however, that the term “self-powered biosensor” is somewhat misleading. While it is true that it is not necessary to apply a potential difference to the electrochemical cell (i.e. they are galvanic cells), measurement of the electrochemical response does require external power. Recently, Pellitero and coworkers developed a true self-powered biosensor based on an enzymatic biofuel cell. They ingeniously coupled a mediated GOx anode with a transparent indium tin oxide cathode in which Prussian blue is reduced to its colorless form (sometimes referred to as Prussian white). The geometrical arrangement of their electrodes and electrolyte (loaded in a lateral flow membrane) allows to use their cathode as an electrochromic display, in which the discolored distance is proportional to the glucose concentration of the sample [176].

Finally, it must be noted that, in parallel with the advances in enzymatic electrodes for fuel cells, significant research has been conducted in the use of enzymatic bioelectrodes as components of electrolytic biosensors [177]. The main difference is that, in this case, electrodes are used as part of an electrolytic cell, rather than a galvanic one. Therefore, a potential is typically applied and chronoamperometric measurements used to obtain the analytical signal. Although seemingly distinct, both fields share many common interests and challenges, including increasing the current output and achieving better stability.