low-voltageoperation

1. Outline • Introduction and motivation • Electrochemical sensing • Microscopic picture of graphene-based electrochemical sensors • Low-voltage operation of graphene-based sensors • Future directions

2. Why electrochemical sensors? • Simple structures and easy to miniaturize: high spatial resolution • Simple operation: direct analyte detection without surface modification, inexpensive instrumentation • Inherent specificity using potential sweep methods • Potential for high temporal resolution

3. Basic experimental set up with an electrochemical sensor Working electrode Reference electrode Electrolytic solution

4. Background current (1/3) Ionic solution + + + Conductive material (Electrode) + + + + Diffusive layer Helmholtz Layer

5. Background current current (2/3) Applied ramp potential + A V - Recorded current [1]

6. Background current current (3/3) Applied waveform Measured current i(t) [1]

7. Fast-scan cyclic voltammetry FSCV waveform Time Current Voltage RedoxCurrent Current [2] Voltage Voltage

8. Macroscopic model of electrochemical sensor General sequence of an electrochemical reaction [1].

9. Electron transfer microscopic model • Schematic showing the insight of the electron transfer process[3].

10. Quantum mechanical tunneling • The tunneling current can be calculated as: Φ1 Φ2 Φ1 Φ2

11. Graphene-based sensorDefect as electrochemical active sites • Example of structural defect in a graphene-based sensor [4].

12. Device fabrication

13. Dopamine measurement

14. Graphene-based sensorNew microscopical model (experimental results)

15. Graphene-based sensorNew microscopical model (theory) [8]

16. Graphene-based sensorNew microscopical model (theory)

17. Graphene-based sensorNew microscopical model (theory)

18. Low-voltage operation of graphene-based sensors Measured background current at Vpeak= 1.3 V Measured background current at Vpeak= 0.6 V

19. Enhanced sensitivityExperimental results Electrochemical currents obtained measuring dopamine at different anodic voltages

20. Enhanced sensitivityPhysical explanation Diffusive layer Helmholtz Layer Graphitic sensor

21. Enhanced sensitivityAgreement between simulations and experimental results

22. Serotonin voltage dependence

23. N-shape waveformSuppression of the main oxidation peak of 5-HT

24. Monotonically voltage dependence of serotonin

25. Generality of voltage dependence

26. Low-voltage operationImproved specificity

27. Low voltage operationHigh background current stability and robustness to bio-fouling

28. Future directions (1/2)In vivo measurements Example of fabricated neural probe with 8 graphene-based sensors

29. Moiré period depends on the twisted angle The moire’lattice depends on the twisted angle. The lattice constant can be found as: https://www.youtube.com/watch?v=DsRiC9d2-cU

30. References • A. J. Bard, L. R. Faulkner, J. Leddy, and C. G. Zoski. Electrochemical methods: fundamentals and applications Vol. 2. wiley New York, 1980. • Roberts, James G., et al. "Real-time chemical measurements of dopamine release in the brain." Dopamine. Humana Press, Totowa, NJ, 2013. 275-294 • H Gerischer.In Adv. Electrochem. Electrochem. Eng.; P. Delahay, Ed 1961 • Wu, T., Alharbi, A., Kiani, R. and Shahrjerdi, D., 2019. Quantitative Principles for Precise Engineering of Sensitivity in Graphene Electrochemical Sensors. Advanced Materials, 31(6), p.1805752. • Kim, K., DaSilva, A., Huang, S., Fallahazad, B., Larentis, S., Taniguchi, T., Watanabe, K., LeRoy, B.J., MacDonald, A.H. and Tutuc, E., 2017. Tunable moiré bands and strong correlations in small-twist-angle bilayer graphene. Proceedings of the National Academy of Sciences, 114(13), pp.3364-3369.