ZnO nanorods as immobilization layers for interdigitated capacitive immunosensors

• We attached ZnO nanorods to interdigitated capacitor microelectrodes.
• The proposed micrometer approach is an advantage over nanometer immunosensors.
• Antibodies were crosslinked to the ZnO nanorods which were stable during testing.
• The immunosensors identified the target antigen by a decrease in the capacitance.
• Maximum variation of the capacitance of the immunosensor was achieved at 6 kHz.

ZnO nanorod structures were deposited on micrometer interdigitated Au electrodes to function as three-dimensional matrixes for the immobilization of antibodies in a capacitive immunosensor format. As a proof of concept, anti-horseradish peroxidase (anti-HRP) antibodies were immobilized on the ZnO nanostructured surface by a crosslinking process. The ZnO nanorod layer allows distribution of antibodies across the entire region probed by the measuring electric field applied to the microelectrodes. This is an alternative approach to the use of more expensive nanometer electrodes necessary in the detection of smaller layers of antibodies. The new micrometer interdigitated capacitive immunosensor was able to discriminate between HRP antigen in buffer; a non-specific antigen in buffer; or buffer alone, as proven by capacitance measurements. Maximum response of the sensor was achieved in the 5–6 kHz frequency range, opening the possibility for a simplified single frequency detection system for direct antigen detection in complex biological samples.