A nanostructured signal-responsive thin hydrogel membrane was coupled with enzyme-based systems to yield "smart" multisignal-responsive hybrid systems with built-in "logic". The enzyme systems transduce biochemical input signals into structural changes of the membrane, thus resulting in the amplification of the biochemical signals and their transformation into the gated transport of molecules through the membrane. Coupling of the biocatalytic systems with a stimuli-responsive membrane is a promising approach for the development of materials that can regulate transport and release of chemicals/drugs by receiving and processing the biochemical information via biochemical reactions.

A switchable bioelectrocatalytic system for glucose oxidation controlled by external biochemical signals exemplifies interfacing between bioelectronic and biochemical ensembles.

The development of a highly parallel enzyme logic sensing concept employing a novel encoding scheme for the determination of multiple pathophysiological conditions is reported. The new concept multiplexes a contingent of enzyme-based logic gates to yield a distinct 'injury code' corresponding to a unique pathophysiological state as prescribed by a truth table. The new concept is illustrated using an array of NAND and AND gates to assess the biomedical significance of numerous biomarker inputs including creatine kinase, lactate dehydrogenase, norepinephrine, glutamate, alanine transaminase, lactate, glucose, glutathione disulfide, and glutathione reductase to assess soft-tissue injury, traumatic brain injury, liver injury, abdominal trauma, hemorrhagic shock, and oxidative stress. Under the optimal conditions, physiological and pathological levels of these biomarkers were detected through either optical or electrochemical techniques by monitoring the level of the outputs generated by each of the six logic gates. By establishing a pathologically meaningful threshold for each logic gate, the absorbance and amperometric assays tendered the diagnosis in a digitally encoded 6-bit word, defined as an 'injury code'. This binary 'injury code' enabled the effective discrimination of 64 unique pathological conditions to offer a comprehensive high-fidelity diagnosis of multiple injury conditions. Such processing of relevant biomarker inputs and the subsequent multiplexing of the logic gate outputs to yield a comprehensive 'injury code' offer significant potential for the rapid and reliable assessment of varied and complex forms of injury in circumstances where access to a clinical laboratory is not viable. While the new concept of parallel and multiplexed enzyme logic gates is illustrated here in connection to multi-injury diagnosis, it could be readily extended to a wide range of practical medical, industrial, security and environmental applications.

The pH-responsive nanoparticles were coupled with information-processing enzyme-based systems to yield "smart" signal-responsive hybrid systems with built-in Boolean logic. The enzyme systems performed AND/OR logic operations, transducing biochemical input signals into reversible structural changes (signal-directed self-assembly) of the nanoparticle assemblies, thus resulting in the processing and amplification of the biochemical signals. The hybrid system mimics biological systems in effective processing of complex biochemical information, resulting in reversible changes of the self-assembled structures of the nanoparticles. The bioinspired approach to the nanostructured morphing materials could be used in future self-assembled molecular robotic systems.

The logic gates NAND/NOR were mimicked by enzyme biocatalyzed reactions activated by sucrose, maltose and phosphate. The subunits performing AND/OR Boolean logic operations were designed using maltose phosphorylase and cooperative work of invertase/amyloglucosidase, respectively. Glucose produced as the output signal from the AND/OR subunits was applied as the input signal for the INVERTER gate composed of alcohol dehydrogenase, glucose oxidase, microperoxidase-11, ethanol and NAD(+), which generated the final output in the form of NADH inverting the logic signal from 0 to 1 or from 1 to 0. The final output signal was amplified by a self-promoting biocatalytic system. In order to fulfill the Boolean properties of associativity and commutativity in logic networks, the final NADH output signal was converted to the initial signals of maltose and phosphate, thus allowing assembling of the same standard units in concatenated sequences. The designed modular approach, signal amplification and conversion processes open the way toward complex logic networks composed of standard elements resembling electronic integrated circuitries.

The modified electrode for electrocatalytic oxidation of NADH was developed using a pH-switchable redox interface. The operation of the modified electrode was controlled by logic operations performed by enzyme systems processing biochemical input signals. The electrocatalytic oxidation of NADH was activated upon appropriate combinations of the signals processed by the AND/OR logic operations performed by the enzymes. The modified interface was reset in a mute nonactive state by another enzyme reaction. The coupling between the enzyme logic systems and the bioelectrocatalytic interface was achieved by pH changes produced in situ by the enzyme reactions, resulting in different protonation states of the polymeric matrix associated with the electrode surface. The bioelectrocatalytic system integrated with biochemical computing systems opens the way to novel "smart" interfaces for multisignal biosensors and signal-controlled biofuel cells. In a long perspective, this approach will allow physiological control of implantable bioelectronic devices.

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A multi-enzyme biocatalytic cascade processing simultaneously five biomarkers characteristic of traumatic brain injury (TBI) and soft tissue injury (STI) was developed. The system operates as a digital biosensor based on concerted function of 8 Boolean AND logic gates, resulting in the decision about the physiological conditions based on the logic analysis of complex patterns of the biomarkers. The system represents the first example of a multi-step/multi-enzyme biosensor with the built-in logic for the analysis of complex combinations of biochemical inputs. The approach is based on recent advances in enzyme-based biocomputing systems and the present paper demonstrates the potential applicability of biocomputing for developing novel digital biosensor networks.