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Interdigital (IDT) microsensors are one of the most commonly used periodic microelectrode devices in a wide range of fields such as microelectromechanical systems (MEMS), telecommunications, chemical sensing, etc. IDT biochemical sensors targeted towards the direct detection of immobilized ssDNA (single strand nucleic acid sequences) and the subsequent hybridization with the complementary strand are currently an area of significant research interest. The most common outputs of measurement are changes in resistance and capacitance between electrodes as a result of changes in the conductivity or dielectric constant of a thin layer of material or solution coating the IDT device, which contains the oligomeric DNA of interest. DNA may be immobilized on both the electrode surfaces and the interdigital spaces or only on the latter, depending on the method used for the chemical modification of the sensor surface. In this work, various IDT designs are explored from the point of view of sensitivity to the changes in impedance associated with modifications in the conductivity of the material near the electrodes. The designs are studied by an electroquasistatics, finite element method-based 3D model to simulate the variation of IDT sensor impedance. A range of device geometries are considered, with particular attention paid to the width of the fingers relative to the period, or metallization ratio. Our results show that low metallization ratios lead to better impedance sensitivity. The simulation models have also been checked experimentally with commercially available IDTs, where a good agreement has been obtained between calculated and measured impedance.
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