Microelectrodes are multi-purpose electrochemical / electronic devices that can be operated under diverse environmental conditions for an enormous variety of applications. We use mainly three types of chip based 2D multi-electrode systems for the detection of analyte molecules including silicon based multi-electrode array (MEA), flexible multielectrode array (flexMEA) and interdigitated electrode (IDE) array. All types of electrode chips are fabricated by cleanroom microfabrication technology at the Helmholtz Nanoelectronic facility (HNF) of the Forschungszentrum Juelich GmbH.

Multi-electrode array (MEA)

Our MEA chip has a size of (24 × 24) mm² and the electrode array is located in the central sensor area with the size of (1.4 × 1.4) mm² possessing 64 equidistant gold microelectrodes. Each microelectrode can be independently electrically addressed and used to record simultaneously up to 64 channels. The electrodes are arranged in an array pattern of 8×8 electrodes. The chip is passivated by a dielectric layer against the analyte solution. The active areas of the microelectrodes are defined by small hole-like openings in the dielectric layer with a diameter ranging from 3 µm to 24 μm. MEAs own many advantages over macroelectrodes, such as enhanced signal-to-noise ratio, high mass-transfer rate, spatial resolution, and redundant sensor signals. We modify the electrode surface by various receptor molecules such as aptamers to facilitate multi-targets detection of related biomarkers or neurotransmitters.

Microelectrode arrays — MEA chip (24 × 24 mm2) and the electrode array (1.4 × 1.4 mm2) possessing 8x8 gold microelectrodes and the active area of the microelectrode with small hole-like opening (diameter of 3µm - 24μm).

Flexible multielectrode array (flexMEA)

The manufacturing of the multi-electrode arrays (MEA) on soft polymer substrates promises low fabrication costs, and allows a relatively ease realization of a multi-target detection by a single biosensor. We have developed a flexible multielectrode array (flex-MEA) that can be partially divided into four sets of electrodes. The partially divided sets of electrodes of the flex-MEA chip can be incubated separately in different aptamer solutions. The resulting sensor chip carries then individually addressable electrodes with different receptors which can be used to detect label-free multiple biomarkers as demonstrated with the developed multi-target malaria aptasensor.

Interdigitated electrodes (IDEs)

Interdigitated electrodes (IDEs) are an array of nano- or microelectrodes with a zipper-like or comb-shaped arrangement. Depending on the design, IDEs can be utilized as impedance or capacitance biosensors for analyte detection or as electrode arrays to perform electrical characterization of objects with very small dimensions (neurons, conductive protein fibers, and conductive polymers). Impedimetric or capacitive biosensors are extremely sensitive even to low concentrations of analyte and can be relatively easily and cheaply produced. Such electrodes usually have two, rarely three terminals. In arrays of IDEs for electrical characterization each electrode can be addressed separately. This gives a huge advantage in the possibility of assessing charge transport over various distances without moving the sample. This also allows estimating contact resistance and finding the best place of contact of a sample with the electrodes. IDEs are very promising for designing miniaturized sensors and investigating intrinsic properties of electrically-conductive biological structures on a very small scale.