Miniaturized probe on polymer SU-8 with array of individually addressable microelectrodes for electrochemical analysis in neural and other biological tissues

An SU-8 probe with an array of nine, individually addressable gold microband electrodes (100 mu m long, 4 mu m wide, separated by 4-mu m gaps) was photolithographically fabricated and characterized for detection of low concentrations of chemicals in confined spaces and in vivo studies of biological tissues. The probe's shank (6 mm long, 100 mu m wide, 100 mu m thick) is flexible, but exhibits sufficient sharpness and rigidity to be inserted into soft tissue. Laser micromachining was used to define probe geometry by spatially revealing the underlying sacrificial aluminum layer, which was then etched to free the probes from a silicon wafer. Perfusion with fluorescent nanobeads showed that, like a carbon fiber electrode, the probe produced no noticeable damage when inserted into rat brain, in contrast to damage from an inserted microdialysis probe. The individual addressability of the electrodes allows single and multiple electrode activation. Redox cycling is possible, where adjacent electrodes serve as generators (that oxidize or reduce molecules) and collectors (that do the opposite) to amplify signals of small concentrations without background subtraction. Information about electrochemical mechanisms and kinetics may also be obtained. Detection limits for potassium ferricyanide in potassium chloride electrolyte of 2.19, 1.25, and 2.08 mu M and for dopamine in artificial cerebral spinal fluid of 1.94, 1.08, and 5.66 mu M for generators alone and for generators and collectors during redox cycling, respectively, were obtained.

Automated summary

The SU-8 probe with an array of nine individually addressable gold microband electrodes was used for detecting low concentrations of chemicals and studying biological tissues. The probe, flexible but sharp, could be inserted into soft tissue without noticeable damage. Redox cycling using adjacent electrodes allowed signal amplification without background subtraction, providing information on electrochemical mechanisms and kinetics. Detection limits for specific compounds were successfully obtained.