Graphene-based electrodes for ECG signal monitoring: Fabrication methodologies, challenges and future directions

Figures & data

Figure 1. Fabrication of electrodes using screen printing technique.

Table 1. Electrical properties of the electrodes fabricated by screen printing method

Sl. No.	Material used for electrode fabrication	Ref.	Sheet resistance	Quality of ECG signal
1.	Fine graphene ink prepared from graphene nanoplatelets	(Goyenola et al., 2011)	–	The Pearson correlation co-efficient between this electrode and Ag/AgCl electrode is found to be 99.47%.
2.	Fine graphene ink screen printed onto textile fabric precoated with a polymer layer	(Xu et al., 2020)	418 ± 21 Ω/sq (after one printing process) 96 ± 8 Ω/sq (after four printing process)	–
3.	Graphene oxide (GO) and silver nanowires (AgNWs)	(Xu et al., 2019)	28Ω/sq (after one printing process) and 11.9 Ω/sq (after two printing process)	–
4.	Graphene/graphite and PEDOT:PSS	(Sinha et al., 2019)	5.5 Ω/sq	SNR = 23.71 dB

Figure 2. Fabrication of electrodes following the dip coating method.

Table 2. Electrical properties of electrodes fabricated by the dip coating method

Sl. No.	Material used for electrode fabrication	Quality of ECG signal	Sheet resistance/Conductivity	Ref.	Impedance
1.	Reduced graphene oxide clad textile	The Pearson correlation co-efficient between this electrode and Ag/AgCl electrode is found out to be 97%.	Conductivity 4.5 S/cm	(Yapici et al., 2015)	87.5 kΩ to 11.6 kΩ in the frequency range of 1Hz to 1kHz. For Ag/AgCl electrode 5.9 kΩ to 2.2 kΩ in the same frequency range
2.	Graphene and PEDOT:PDMS coated textile electrode	-	Sheet resistance 11.51 Ω/sq	(Lam et al., 2017)	-
3.	Graphene oxide- porous PDMS thin film	-	Sheet resistance 1.5 kΩ/sq	(Yun et al., 2017)	-
4.	Reduced graphene oxide clad textile as wearable medical garment	Cross-correlation of 88% for the whole waveform and the maximum value of 97% was measured between two P-QRS-T segments when compared between wearable electrodes and conventional wet ECG electrodes	-	(Yapici & Alkhidir, 2017)	87.5 kΩ to 55 kΩ in the frequency range of 10–50 Hz. For Ag/AgCl electrode.9 kΩ to 20 kΩ in the same frequency range 50.9 kΩ to 20 kΩ in the same frequency range

Figure 3. Electrode fabrication using the wet transfer method.

Table 3. Electrical properties of electrodes fabricated by wet transfer method

Sl. No.	Material used for electrode fabrication	SNR Value of ECG signal	Sheet resistance or conductivity	Ref.	Skin Contact Impedance
1.	CVD grown graphene layer transferred on Ag layer	Graphene coated Ambu type electrodes- 27.03 dB Wet Ag/AgCl Ambu type electrodes- 25.21 dB Graphene coated Covidien type electrode- 25.32 dB Wet Ag/AgCl Covidien type electrodes- 21.23 dB	Conductivity 6.94×10^4S/m	(Celik et al., 2016)	In the frequency range of 20 Hz to 1 kHz -Commercial Ag/AgCl electrodes - from 445.05 kΩ to 13.82 kΩGraphene coated electrodes - from 65.82 kΩ to 5.10 kΩ Commercial Ag/AgCl electrodes - from 445.05 kΩ to 13.82 kΩ Graphene coated electrodes - from 65.82 kΩ to 5.10 kΩ
2.	CVD grown graphene layer transferred on PET substrate	Commercial Ag/AgCl electrodes- 31dB Graphene coated PET electrode- 31.6 dB	-	(Lou et al., 2016)	In the frequency range of 10 Hz to 1kHz –Commercial Ag/AgCl electrodes - from 55.1 kΩ to 18.2 kΩGraphene-based electrode - from 281.8 kΩ to 24.8 kΩ Commercial Ag/AgCl electrodes - from 55.1 kΩ to 18.2 kΩ Graphene-based electrode - from 281.8 kΩ to 24.8 kΩ
3.	PEDOT:PSS transferred CVD grown graphene film(PTG)	-	Sheet resistance ~45 Ω/sq	(Zhao et al., 2021)	Conventional Ag/AgCl electrodes- 45 kΩ at 100HzPTG electrodes- 32 kΩ at 100 Hz PTG electrodes- 32 kΩ at 100 Hz

Figure 4. Electrode fabrication following wet transfer and dry patterning technique (Qiao et al., 2018).

Table 4. Electrical properties of electrodes fabricated by wet transfer and dry patterning method

Sl. No	ECG electrodes	SNR of the ECG signal	Bio-Z measurements	Ref.	Skin Contact Impedance
1.	Graphene electronic tattoo (GET)	Graphene-based electrophysiological sensors (GEPS)- 15.22 dB Conventional Ag/AgCl electrodes- 11dB	-	(Lu et al., 2017; Qiao et al., 2018)	The skin contact impedance of graphene epidermal electronic system was comparable with conventional wet Ag/AgCl electrodes
2.	Bilayer graphene electronic tattoo(BiGET)	-	Average standard deviation – BiGET- 3.6 mΩ Ag/AgCl − 4.1mΩ	(Sel et al., 2019)	The fabricated bilayer GETs offered skin contact impedance of 10kΩ at 10kHz which is comparatively lower than the commercial Ag/AgCl electrodes.

Figure 5. Fabrication of electrodes using spray coating technique.

Figure 6. Spin coating technique for fabricating electrodes.

Figure 7. Electrode fabrication using drop casting technique.

Table 5. Electrical properties of electrodes fabricated by drop casting method

Sl. No.	ECG electrode	Quality of the ECG signal	Ref.	Skin contact Impedance
1.	Graphene based PDMS electrode	The average value of the R-wave Ag/AgCl electrode- 0.704 mV Graphene polymer film electrode- 0.662 mV	(Liu et al., 2018)	In the frequency range of .1 Hz to 1kHz, Commercial wet gel electrodes- from 1kΩ to 200 Ω and Graphene-based polymer electrode- from 20k Ω to 30k Ω
2.	Graphene nanoribbon and PVA based electrode (PVA/GNR)	SNR value Ag/AgCl electrodes: 62.22dB PVA/GNR (1%) electrodes: 59.99 dB	(Prasad et al., 2021)	In the frequency range of 10Hz to 1kHzWet Ag/AgCl electrodes from 400 Ω to 250 Ω PVA/GNR electrode- constant skin contact impedance value Wet Ag/AgCl electrodes from 400 Ω to 250 Ω PVA/GNR electrode- constant skin contact impedance value
3.	Laser-reduced graphene oxide(rGO) and PET based electrode	SNR value for rGO bioelectrode is above 70 dB	(Murastov et al., 2020)	4k Ω
4.	Graphene based textile electrode	The ECG signals extracted from GT electrode and Ag/AgCl electrode were comparable.	(Wei et al., 2021)	-
5.	AgNRs/RGO-PDMS flexible dry electrodes	High-quality, distinguishable and stable ECG signal	(Maithani et al., 2022)	In the frequency range of 40Hz to 1 kHzwet Ag/AgCl electrodes- from 28.4 ± 2.7 k Ω to 7.6 ± 0.9 kΩAgNRs/RGO-PDMS flexible dry electrodes - from 7.1 ± .7 k Ω to 5.6 ± 1.7 k Ω wet Ag/AgCl electrodes- from 28.4 ± 2.7 k Ω to 7.6 ± 0 0.9 k Ω AgNRs/RGO-PDMS flexible dry electrodes - from 70.1 ± 0.7 k Ω to 5.6 ± 1.7 k Ω
6.	Flexible 3D porous graphene (3DPG) electrode incorporating PEP	SNR value - 3DPG electrode- 8 dB PEP/3DPG electrode- 13.5 dB Wet Ag/AgCl electrodes- 13.9dB.	(Zahed et al., 2021)	In the frequency range of 4 Hz to 1 kHzPEP/3DPG electrodes- from 198.2k Ω to 90.35k Ω Wet Ag/AgCl electrodes- from 1.68 M Ω to 189.6k Ω PEP/3DPG electrodes- from 198.2k Ω to 90.35k Ω Wet Ag/AgCl electrodes- from 1.68 M Ω to 189.6k Ω
7.	Graphene nanoplatelets (GNPs) nanofillers with polyvinylidene fluoride (PVDF) coated clean fabric textile	SNR value - GNP/PVDF (10%) electrode − 36.5 dB GNP/PVDF (13%) electrode − 38.3 dB Wet Ag/AgCl electrode- 34.6dB.	(Ali et al., 2022)	At 20HzGNP/PVDF (10%) − 98.9k Ω GNP/PVDF (13%)- 98.32k Ω GNP/PVDF (10%) − 98.9k Ω GNP/PVDF (13%)- 98.32k Ω

Figure 8. Fabrication of electrodes using ink-jet printing technique.

Figure 9. Electrospinning technique for electrode fabrication.

Figure 10. Electrode fabrication using vacuum filtration and drying technique.

Goyenola, C., Gueorguiev, G. K., Stafström, S., & Hultman, L. (2011). Fullerene-like CSx: A first-principles study of synthetic growth. Chemical Physics Letters, 506(1–3), 86–91. https://doi.org/10.1016/j.cplett.2011.02.059

 Web of Science ®Google Scholar

Xu, X., Luo, M., He, P., & Yang, J. (2020). Washable and flexible screen printed graphene electrode on textiles for wearable healthcare monitoring. Journal of Physics D: Applied Physics, 53(12), 125402. https://doi.org/10.1088/1361-6463/ab5f4a

 Web of Science ®Google Scholar

Xu, X., Liu, Z., He, P., & Yang, J. (2019, November). Screen printed silver nanowire and graphene oxide hybrid transparent electrodes for long-term electrocardiography monitoring. Journal of Physics D: Applied Physics, 52(45), 455401. https://doi.org/10.1088/1361-6463/ab3869

 Web of Science ®Google Scholar

Sinha, S. K., Alamer, F. A., Woltornist, S. J., Noh, Y., Chen, F., McDannald, A., Allen, C., Daniels, R., Deshmukh, A., Jain, M., Chon, K., Adamson, D. H., & Sotzing, G. A. (2019, September). Graphene and Poly(3,4-ethylene dioxythiophene): Poly(4-styrenesulfonate) on nonwoven fabric as a room temperature metal and its application as dry electrodes for electrocardiography. ACS Applied Materials and Interfaces, 11(35), 32339–32345. https://doi.org/10.1021/acsami.9b05379

 PubMed Web of Science ®Google Scholar

Yapici, M. K., Alkhidir, T., Samad, Y. A., & Liao, K. (2015). Graphene-clad textile electrodes for electrocardiogram monitoring. Sensors and Actuators B: Chemical, 221, 1469–1474. https://doi.org/10.1016/j.snb.2015.07.111

 Web of Science ®Google Scholar

Lam, C. L. (2017). Graphene ink-coated cotton fabric-based flexible electrode for electrocardiography. In 2017 5th International Conference on Instrumentation, Communications, Information Technology, and Biomedical Engineering (ICICI-BME) (pp. 73–75). https://doi.org/10.1109/ICICI-BME.2017.8537771

 Google Scholar

Yun, Y. J., Ju, J., Lee, J. H., Moon, S.-H., Park, S.-J., Kim, Y. H., Hong, W. G., Ha, D. H., Jang, H., Lee, G. H., Chung, H.-M., Choi, J., Nam, S. W., Lee, S.-H., & Jun, Y. (2017, September). Highly elastic graphene-based electronics toward electronic skin. Advanced Functional Materials, 27(33), 1701513. https://doi.org/10.1002/adfm.201701513

 Web of Science ®Google Scholar

Yapici, M. K., & Alkhidir, T. E. (2017). Intelligent medical garments with graphene-Functionalized smart-Cloth ECG Sensors. Sensors, 17(4). https://doi.org/10.3390/s17040875

 PubMed Web of Science ®Google Scholar

Celik, N., Manivannan, N., Strudwick, A., & Balachandran, W. (2016). Graphene-enabled electrodes for electrocardiogram monitoring. Nanomaterials, 6(9). https://doi.org/10.3390/nano6090156

 Web of Science ®Google Scholar

Lou, C., Li, R., Li, Z., Liang, T., Wei, Z., Run, M., Yan, X., & Liu, X. (2016, November). Flexible graphene electrodes for prolonged dynamic ECG monitoring. Sensors (Basel), 16(11), https://doi.org/10.3390/s16111833

 Web of Science ®Google Scholar

Zhao, Y., Zhang, S., Yu, T., Zhang, Y., Ye, G., Cui, H., He, C., Jiang, W., Zhai, Y., Lu, C., Gu, X., & Liu, N. (2021). Ultra-conformal skin electrodes with synergistically enhanced conductivity for long-time and low-motion artifact epidermal electrophysiology. Nature Communications, 12(1), 4880. https://doi.org/10.1038/s41467-021-25152-y

 PubMed Web of Science ®Google Scholar

Qiao, Y., Wang, Y., Tian, H., Li, M., Jian, J., Wei, Y., Tian, Y., Wang, D.-Y., Pang, Y., Geng, X., Wang, X., Zhao, Y., Wang, H., Deng, N., Jian, M., Zhang, Y., Liang, R., Yang, Y., & Ren, T.-L. (2018, September). Multilayer graphene epidermal electronic skin. Agricultural Science & Technology Nano, 12(9), 8839–8846. https://doi.org/10.1021/acsnano.8b02162

 Google Scholar

Lu, N., Ameri, S. K., Ha, T., Nicolini, L., Stier, A., & Wang, P. (2017, April). Epidermal electronic systems for sensing and therapy. Proceedings, 10167, 101670. https://doi.org/10.1117/12.2261755

 Google Scholar

Sel, K., Kireev, D., Brown, A., Ibrahim, B., Akinwande, D., and Jafari, R. (2019). Electrical characterisation of graphene-based e-Tattoos for bio-impedance-based physiological sensing. In 2019 IEEE Biomedical Circuits and Systems Conference (BioCAS) (pp. 1–4). https://doi.org/10.1109/BIOCAS.2019.8919003

 Google Scholar

Liu, B. Y., Luo, Z. Y., Zhang, W. Z., Tu, Q., & Jin, X. (2018). A simple method of fabricating graphene-polymer conductive films. International Polymer Processing, 33(1), 135–138. https://doi.org/10.3139/217.3418

 Web of Science ®Google Scholar

Prasad, A. S., Jayaram, M. N., & N, K. S. (2021). Fabrication of GNR electrode for ECG signal acquisition. IEEE Sensors Letters, 5(9), 1–4. https://doi.org/10.1109/LSENS.2021.3103841

 PubMedGoogle Scholar

Murastov, G., Bogatova, E., Brazovskiy, K., Amin, I., Lipovka, A., Dogadina, E., Cherepnyov, A., Ananyeva, A., Plotnikov, E., Ryabov, V., Rodriguez, R. D., & Sheremet, E. (2020, October). Flexible and water-stable graphene-based electrodes for long-term use in bioelectronics. Biosensors & Bioelectronics, 166, 112426. https://doi.org/10.1016/j.bios.2020.112426

 PubMed Web of Science ®Google Scholar

Wei, Y., Li, X., Wang, Y., Hirtz, T., Guo, Z., Qiao, Y., Cui, T., Tian, H., Yang, Y., & Ren, T.-L. (2021, November). Graphene-based multifunctional textile for sensing and actuating. Agricultural Science & Technology Nano, 15(11), 17738–17747. https://doi.org/10.1021/acsnano.1c05701

 Google Scholar

Maithani, Y., Mehta, B. R., & Singh, J. P. (2022). Implementation of hybrid Ag nanorods embedded RGO-PDMS conductive material for flexible and dry electrocardiography sensor. Materials Letters: X, 15, 100152. https://doi.org/10.1016/j.mlblux.2022.100152

 Google Scholar

Zahed, M. A., Barman, S. C., Sharifuzzaman, M., Zhang, S., Yoon, H., Park, C., Yoon, S. H., & Park, J. Y. (2021, June). Polyaziridine-encapsulated phosphorene-incorporated flexible 3D porous graphene for multimodal sensing and energy storage applications. Advanced Functional Materials, 31(25), 2009018. https://doi.org/10.1002/adfm.202009018

 Web of Science ®Google Scholar

Ali, B., Bidsorkhi, H. C., D’Aloia, A. G., Laracca, M., and Sarto, M. S. (2022). Graphene-based flexible dry electrodes for biosignal detection. In 2022 IEEE International Conference on Flexible and Printable Sensors and Systems (FLEPS) (pp. 1–27). https://doi.org/10.1109/FLEPS53764.2022.9781538.

 Google Scholar