The activity of cytokines in the human body can be associated with certain diseases such as cancer, autoimmune, and infectious disease [1]. Recent studies found that it was possible to non-invasively detect certain cytokines such as Il6 through human saliva and sweat [2]. However, detection of cytokine in such bodily fluid poses a challenge due to very low cytokine concentration, ranging from fg/ml to pg/ml. Thus, signal amplification is necessary to achieve high sensitivity in cytokine detection. In this study, we propose a microfabricated electrochemical sensor with array of platinum micro-well as working electrode (Figure 1a and b). The charge transfer current density is compared to commonly used interdigitated electrode configuration (Figure 1c). A COMSOL model was developed to analytically compare charge transfer current for both electrode type. The electrodes were then compared experimentally through square wave voltammetry measurement.

Method

The microelectrode chips consist of platinum electrode and silicon nitride as insulation layer was fabricated using standard microfabrication techniques. The well array electrode consists of 1024 (32x32) array of 50 μm diameter well (counter electrode) and 2 μm ledge width for ring working electrode. The interdigitated electrode has 30 μm width and 1000 μm length with 10 parallel fingers. Square wave voltammetry measurement was carried using 20 mM Potassium Ferricyanide/ Ferrocyanide as redox probe, dissolved in 1x PBS and Ag/AgCl used as a reference electrode. Scanning range was set between 0 to 0.5 V with 5 mV step size, 25 mV pulse amplitude, and scanning 10 Hz frequency.

Results and Conclusions

Based on experimental results the well microelectrode configuration has 187% higher current density compared to its interdigitated electrode counterpart. The low current amplitude issue of well microelectrode is solved by having an array of 1024 well microelectrode (32x32) which amplify the signal from nanoampere to microampere scale.

References

[1] Monastero, R. N., & Pentyala, S. (2017). Cytokines as Biomarkers and Their Respective Clinical Cutoff Levels. International Journal of Inflammation, 2017, 1–11. doi:10.1155/2017/4309485

[2] Dutta, N., Lillehoj, P. B., Estrela, P., & Dutta, G. (2021). Electrochemical Biosensors for Cytokine Profiling: Recent Advancements and Possibilities in the Near Future. Biosensors, 11(3), 94. https://doi.org/10.3390/bios11030094