Development of Miniaturized Interdigitated Electrode Sensors and Their Application in Taste Sensing

Abstract

Interdigitated Electrodes (IDEs) or Interdigitated Arrays (IDAs) are frequently used in a variety of sensing mechanisms including electrochemical detection and have been subjected to extensive miniaturization in recent times. Multiple methods involving the fabrication of IDEs have been reported. However, these fabrication methods are often time consuming, multistep, skill intensive, expensive and require clean room conditions. This work reports on the fabrication and comparison of miniaturized IDEs fabricated using two inexpensive and clean room free approaches - inkjet-printing and direct laser writing (DLW) based photolithography. For inkjet-printing approach, a commercially available printed-circuit board (PCB) printer was used with a carbon ink to print the IDEs on a glass slide. For photolithography-based fabrication, a DLW system was used for the fabrication of IDEs on a copper-clad FR4 PCB board. Previously established, validated and reported models were employed for the design of IDEs. The design parameters were selected to optimize sensitivity while striking a balance with the overall size of the sensor. The application of the developed IDE sensors was demonstrated for its taste sensing capability. Sensing of five fundamental tastes, namely salty, sweet, sour, bitter, and umami, was established with electrochemical impedance spectroscopy (EIS). The chemicals which can simulate these fundamental tastes for experimental purposes were identified as sucrose (sweet), sodium chloride (salty), citric acid (sour), L-tryptophan (bitter) and guanosine monophosphate (GMP) (umami). EIS was performed on a benchtop electrochemical workstation with two electrode configurations and data was analysed in the frequency range of 1 Hz to 1 MHz. The obtained data was analyzed for different chemicals at varying concentrations and compared for changes in the response. DLW photolithography-based approach produces IDEs with excellent geometric dimensional repeatability. The IDEs produced on glass slides using Carbon ink-based printing were fabricated in under 2 minutes and cost less than US$ 0.3. Both approaches demonstrate the applications of IDEs with fairly reasonable and benchmarked taste sensing capabilities.Figure: a) Optimised Design b) Carbon ink-based printing c) IDE printed on glass slide d) Photlithography based DLW IDE fabrication e) IDE on a copper cladded FR4 PCR board. Figure 1