Implantable biofuel cells have been suggested as sustainable micropower sources operating in living organisms, but such bioelectronic systems are still exotic and very challenging to design. Very few examples of abiotic and enzyme-based biofuel cells operating in animals in vivo have been reported. Implantation of biocatalytic electrodes and extraction of electrical power from small living creatures is even more difficult and has not been achieved to date. Here we report on the first implanted biofuel cell continuously operating in a snail and producing electrical power over a long period of time using physiologically produced glucose as a fuel. The "electrified" snail, being a biotechnological living "device", was able to regenerate glucose consumed by biocatalytic electrodes, upon appropriate feeding and relaxing, and then produce a new "portion" of electrical energy. The snail with the implanted biofuel cell will be able to operate in a natural environment, producing sustainable electrical micropower for activating various bioelectronic devices.

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An ultrasensitive method for the detection of the cholera toxin (CT) using electrochemical or microgravimetric quartz crystal microbalance transduction means is described. Horseradish peroxidase (HRP) and GM1-functionalized liposomes act as catalytic recognition labels for the amplified detection of the cholera toxin based on highly specific recognition of CT by the ganglioside GM1. The sensing interface consists of monoclonal antibody against the B subunit of CT that is linked to protein G, assembled as a monolayer on an Au electrode or an Au/ quartz crystal. The CT is detected by a "sandwich-type" assay on the electronic transducers, where the toxin is first bound to the anti-CT-Ab and then to the HRP-GM1ganglioside-functionalized liposome. The enzyme-labeled liposome mediates the oxidation of 4-chloronaphthol (2) in the presence of H 2 O 2 to form the insoluble product 3 on the electrode support or the Au/quartz crystal. The biocatalytic precipitation of 3 provides the amplification route for the detection of the CT. Formation of the insulating film of 3 on the electrode increases the interfacial electron-transfer resistance, R et , or enhances the electrode resistance, R′, parameters that are quantitatively derived by Faradaic impedance measurements and chronopotentiometric analyses, respectively. Similarly, the precipitate 3 formed on the Au/quartz crystal results in a mass increase on the transducer that is reflected by a decrease in the resonance frequency of the crystal. The methods allow the detection of the CT with an unprecedented sensitivity that corresponds to 1.0 × 10 -13 M.

An enzyme-based biofuel cell with a pH-switchable oxygen electrode, controlled by enzyme logic operations processing in situ biochemical input signals, has been developed. Two Boolean logic gates (AND/OR) were assembled from enzyme systems to process biochemical signals and to convert them logically into pH-changes of the solution. The cathode used in the biofuel cell was modified with a polymer-brush functionalized with Os-complex redox species operating as relay units to mediate electron transport between the conductive support and soluble laccase biocatalyzing oxygen reduction. The electrochemical activity of the modified electrode was switchable by alteration of the solution pH value. The electrode was electrochemically mute at pH > 5.5, and it was activated for the bioelectrocatalytic oxygen reduction at pH < 4.5. The sharp transition between the inactive and active states was used to control the electrode activity by external enzymatic systems operating as logic switches in the system. The enzyme logic systems were decreasing the pH value upon appropriate combinations of the biochemical signals corresponding to the AND/OR Boolean logic. Then the pH-switchable electrode was activated for the oxygen reduction, and the entire biofuel cell was switched ON. The biofuel cell was also switched OFF by another biochemical signal which resets the pH value to the original neutral value. The present biofuel cell is the first prototype of a future implantable biofuel cell controlled by complex biochemical reactions to deliver power on-demand responding in a logical way to the physiological needs.