# Graphene-Based Flexible Electrode for Electrocardiogram Signal Monitoring
## 3 Discussions and Outlook
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Categories** & **Electrodes (Dry/Wet)** & **Sheet Resistance or Contact Impedance** & **Flexibility** & **Advantages** \\ \hline Commercial electrode & Ag/AgCl gel (wet) [88] & 15 k\(\Omega\) at 1 kHz & Depends on its substrate & Widely used, low cost \\ \hline \multirow{6}{*}{Bionic graphene ECG electrodes} & Gecko-inspired electrode (dry) [36] & \(-\)100 \(\Omega\)-cm & Stretchable and bendable & \(-\)1.3 N/cm\({}^{2}\) adhesion force \\ \cline{2-5}  & Amphibian- and & & Can be attached to skin conformally & 6.6 N/cm\({}^{2}\) adhesion force, waterproof \\ \cline{2-5}  & octopus-inspired electrode (dry) [40] & \(/\) & & \\ \cline{2-5}  & Avian-nest-inspired electrode (dry) [42] & \(-\)150 \(\Omega\)/square & More than 10 attaching and \(\,\)detaching cycles & 30 dB signal-to-noise ratio \\ \cline{2-5}  & Self-healing electrode (wet) [43] & \(/\) & \(>\)5000\% stretchability & High healing efficiency \\ \hline \multirow{6}{*}{Fabric-based graphene ECG electrodes} & Cotton-textless-based electrode (dry) [45] & \(-\)104 \(\Omega\)/square & Over 2000 bending cycles & \begin{tabular}{c} 130 g/m\({}^{2}\) lightweight \\ \end{tabular} \\ \cline{2-5}  & Silk-based electrode (wet) [47] & 96 \(\pm\) 8 \(\Omega\)/square & Can be stretched, compressed, and twisted & High healing efficiency (3 s, 100\%) \\ \cline{2-5}  & Nanofiber-based electrode (dry) [51] & 25 \(\Omega\)/square & More than 3000 repeated uses & Hydrophobic \\ \cline{2-5}  & Nylon-textile-based electrode (dry) [53] & 87.5 k\(\Omega\) to 55 k\(\Omega\) in the 10–50 Hz range & Flexible & Have been integrated into garments \\ \hline \multirow{6}{*}{Biodegradable graphene ECG electrodes} & Ultra-high & \multirow{2}{*}{\(75\,\Omega\)/square, 45.12 k\(\Omega\) at 100 Hz} & Young’s modulus of 8.598 MPa & 60 dB signal-to-noise ratio \\ \cline{2-5}  & Geraphene-PHA (dry) [58] & \(-\)20 k\(\Omega\) along & Flexible & Can be kept for 1–2 years \\ \hline \multirow{6}{*}{Laser-induced/scribed graphene ECG electrodes} & Porous LIG electrode (dry) [62] & 360 \(\Omega\)/cm\({}^{2}\),700 \(\Omega\) & Flexible & Cost-effective \\ \cline{2-5}  & Water-stable & \(-\)4 k\(\Omega\) & Flexible & \begin{tabular}{c} 70 dB signal-to-noise ratio, \\ 100 h monitoring in \\ harsh environment \\ \end{tabular} \\ \cline{2-5}  & Polyaziridine- & 98 2 k\(\Omega\) at 4 Hz to & Bendable & 13.5 dB signal-to-noise ratio \\ \cline{2-5}  & electrode (dry) [65] & 90.35 k\(\Omega\) at 1 kHz & & Bendable \\ \cline{2-5}  & Stretchable LIG electrode (dry) [67] & 51.08 k\(\Omega\) at 10 Hz & High strain sensitivity of 2075 & 20.14 dB initial \\ \hline \multirow{6}{*}{Modified-graphene-based ECG electrodes} & Chemically-modified graphene-CNT electrode (dry) [68] & 75 \(\Omega\)/square, 45.12 k\(\Omega\) at 100 Hz & Flexible & High comfortability and \\ \cline{2-5}  & Environmentally friendly & \multirow{2}{*}{/} & \multirow{2}{*}{Flexible} & \multirow{2}{*}{\
\begin{tabular}{c} ECG signal was received \\ after 30 days of monitoring \\ \end{tabular} } \\ \cline{1-1} \cline{2-5}  & Ecg electrodes & (dry) [69] & & \\ \hline \multicolumn{5}{c}{Intercalation doping electrode (dry) [71]} & 40 \(\Omega\)/square & Can sustain 80\% strain &
\begin{tabular}{c} Durable over 2000 cycles at \\ 30\% strain \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Electrical and mechanical properties of the flexible, graphene-based ECG electrodes mentioned above, with their decided advantages. Through the joint efforts of many researchers, graphene ECG electrodes have developed rapidly in recent years. Their electrical properties, mechanical properties, and stability have been greatly improved. Of course, graphene ECG electrodes still have a lot of room for improvement, and many scientific and engineering issues need to be resolved before they can be used on a scale similar to today's commercial Ag/AgCl gel electrodes.