Table 1.
Summary of various electrode materials with key properties.
| Electrode materials | Electrical properties (impedance @1 kHz) | Biocompatibility | Stability | Biodegradability/ Bioresorbability | Mechanical flexibility/ be-ndability | Young's modulus | Optical Transmission (400–700 nm) | References | |
|---|---|---|---|---|---|---|---|---|---|
| Nanopillars | 13.1 ± 2.7 kΩ-1172.3 ± 241.6 kΩ (0–22.5 μm height) | 14 days in vitro | |||||||
| GNPs | Nanorods | 1.847 kΩ (10,000 μm2 area) | Cytotoxic (depend on the size of GNPs) | 20 times (agarose gel insertion) | Biodegradable | Bendable | 1–10 GPa | Opaque | Zhou et al., 2009; Kim et al., 2010b; Nick et al., 2014; Lee et al., 2016b |
| Nanoflakes | 11.9 ± 1.47 kΩ-249 ± 28.1 kΩ (5–50 μm diameter) | A month | |||||||
| Pt black | 3.5 kΩ (4 mm length, ~100 μm diameter) | Biocompatible | 3 days in vivo | N/A | Bendable | N/A | Opaque | Zhang et al., 2015; Lee et al., 2017a; Zátonyi et al., 2018 | |
| Au/Pt alloy | 0.23 MΩ (20 nm diameter) | Biocompatible | 7 times (ultrasonic treatments) | N/A | N/A | 113.8 GPa | Opaque | Zhao et al., 2016 | |
| Ir/Pt alloy | 80 ± 18 kΩ (13 mm length, 75 μm diameter) | Biocompatible | 12 weeks in vivo | N/A | Bendable | 185.5–189.6 GPa | Opaque | Cassar et al., 2019 | |
| Si nanowires | ~20 MΩ (100 nm−200 nm tip diameter) | Biocompatible | 8 days (rodent neurons) 6 weeks (hiPSC-derived neurons) |
Biodegradable | N/A | 60–240 GPa | Transparent | Sohn et al., 2010; Marcon and Boukherroub, 2014; Liu et al., 2017a | |
| Si NMs | ~50 kΩ-~250 kΩ (2002-5002 μm2) | Biocompatible | A month in vivo | Bioresorbable | Flexible | 3.25–180 GPa (2 nm−25 nm thickness) | Transparent | Yu et al., 2016; Bai et al., 2019 | |
| ITO/PEDOT:PSS | ~ 40 kΩ-~100 kΩ (10–80 μm diameter) | Biocompatible | 4 weeks in vitro | N/A | Flexible | ~77 GPa (on glass) | Transparent (> 80 %) | Li and Chang, 2014; Yang et al., 2017 | |
| PEDOT:PSS/nanostructur-ed Pt | 9.2 kΩ (500 μm diameter) | Biocompatible | 1,500 CV cycles | N/A | Flexible | N/A | Opaque | Boehler et al., 2017 | |
| PPy nanotubes/GNP | ~5 kΩ (300 μm diameter) | Biocompatible | Stable | Biodegradable | Flexible/benda-ble | N/A | N/A | Kojabad et al., 2019 | |
| Diamond | ~ 207.9 kΩ (0.0079 mm2 area) | Biocompatible | Stable | N/A | Flexible (on Parylene C) | ~103 GPa | Opaque | Fan et al., 2020 | |
| Graphene | 243.5 ± 15.9 kΩ (~200 μm diameter) | Biocompatible | 70 days in vivo | N/A | Flexible | ~1 TPa | Transparent (>90%) | Lee et al., 2013a; Park et al., 2014 | |
| CNFs | ~1 MΩ (2 cm length, 25.7 ×16.6 μm2) | Biocompatible | 4 weeks in vivo | Unbiodegradable | Flexible | 6–207 GPa | N/A | Lawrence et al., 2008; Guo et al., 2017; Farzamfar et al., 2019 | |
| CNTs | ~64.5 Ω mm−2 | Biocompatible | Stable | Unbiodegradable | Flexible | 530–700 GPa | Transparent (~60%) | Lawrence et al., 2008; Su et al., 2010; Deng et al., 2011 | |
| Glassy carbon | 11.0 ± 5.4 kΩ (300 μm diameter) | Biocompatible (12 days) | Stable | N/A | Flexible | 20 GPa | Opaque | Vomero et al., 2016, 2017 | |