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Electrochemical-transducer compounds are encapsulated in biocompatible hydrogel structures.

The upper part of the figure depicts a typical sensor array; the lower part of the figure depicts some essential features of the fabrication of the array. Fabrication begins with the formation of microdisk electrodes and associated conductors in gold film on a flexible polyimide sheet by use of established deposition and photolithography techniques. The microdisk electrodes are functionalized with a monolayer of 11 mercaptoundecanoic acid (MUA) then coated with POs-EA, which adheres by strong electrostatic attraction to the MUA. The POS-EA layer is further coated with a mixture comprising PEG-DA, a solution containing GOX, and a photopolymerization initiator. Exposure to ultraviolet light causes cross-linking of the PEG-DA to form the PEG-DA hydrogel that encapsulates GOX.

In tests of a five-element array of individually electrically addressable sensors like the one shown in the figure, no cross-talk between adjacent electrodes was observed. It was found that when sampled together, the electrodes behaved as one large electrode with peak current equivalent to the sum of the currents of the individual electrodes — a characteristic that is especially important for diagnosis of failure of one of the sensors in an array. In other tests, an array was shown to exhibit the desired linear sensitivity to the concentration of glucose in the range of biological interest.

This work was done by Michael V. Pishko of Pennsylvania State University for the Army Research Laboratory. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp under the Bio-Medical category. ARL-0017

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Implantable Electrochemical Sensors for Metabolic Monitoring (reference ARL-0017) is currently available for download from the TSP library.

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