Table 1.
Summary of the performance of microfabricated reference electrodes in the literature.
| Electrode type | Dimensions | Fabrication | Filling solution | Test solution | Electrode potential (V) | Stability | Year | [Ref.] |
|---|---|---|---|---|---|---|---|---|
| Ag/AgCl | 13mm × 1.5mm × 0.4mm | Photolithography, Sputtering, Electrochemical oxidation | None (quasi-RE) | 0.1 M KCl in 20mM NaOH/KH2PO4 buffer, pH 7 | 90mV vs. commercial Ag/AgCl | < 1mV in 24h, 1mV in 8h with saturated AgCl and KCl in solution | 1998 | [64] |
| Ag/AgCl | 13mm × 1.5mm × 0.9mm | Photolithography, Electrochemical oxidation, Bulk micromachining | Saturated KCl, AgCl. Pin hole liquid junction | 0.1 M KCl in 20mM NaOH/KH2PO4 buffer, pH 7 | 7mV vs. commercial Ag/AgCl | <1mV in 3h. | 1998 | [65] |
| Ag/AgCl | 13mm × 1.5mm × 0.9mm | Photolithography, Electrochemical oxidation, Screen printing | Saturated KCl, AgCl. Hydrophillic Polymer liquid junction | 0.1 M KCl in 50mM NaOH/KH2PO4 buffer, pH 7 | 8mV vs. commercial Ag/AgCl | <2mV in 100h. | 1999 | [66] |
| Ag/AgCl | N/A (macroscopic Ag wire used) | Photo-polymerization for junction polymer | 1M KCl. pDADMAC plug junction | PBS at pH 7.4 with 0.15M NaCl | 19.3mV vs. commercial Ag/AgCl in 3M KCl | <12mV in 30h. | 2006 | [69] |
| Ag/AgCl | N/A | Photolithography, Lift-off, Sputtering, Electrochemical oxidation | Saturated KCl in Agarose supporting gel. | 10mM KCl, pH range 4–10 | 0.45mV vs. commercial Ag/AgCl | <1.5mV in 42h. | 2002 | [34] |
| Ag/AgCl | 2cm×0.1 mm | Electroless plating on glass, Electroplating | None (quasi-RE) | 3M KCl | 13.5mV vs. commercial Ag/AgCl | <30mV in 14 days | 2006 | [67] |
| Ag/AgCl | 106 μm2 | Photolithography, Chemical oxidation | None (quasi-RE) | 1mM KCl | 32mV vs. commercial Ag/AgCl at 1mM KCl, with identical electrode variation of 10mV | <2mV in 5000s | 2006 | [48] |
| Ag/AgCl | 1μm diameter capillary | Pre-made capillary and silver wire. Capillary action for salt bridge and filling solution | 3.3M KCl + AgCl | Distilled water | (−4–0) mV vs. commercial Ag/AgCl | <2 mV in 2400s | 2005 | [1] |
| Ag/AgCl | 1.2mm2 | Photolithography, Lift-off, Plasma chlorination | None (quasi-RE) | PBS (0.1M Na2HPO4, 0.15M NaCl, 0.1 g/l NaN3 at pH 7.4) | 70mV vs. commercial Ag/AgCl electrode in 3M KCl | <13mV in 5h | 2003 | [90] |
| Ag/AgCl | 10mm×20mm | Screen-printing thick film | None (quasi-RE) | Technical buffer with 0.05mM Cl− | ≈230mV vs. commercial Ag/AgCl | <70mV in 12h | 2001 | [91] |
| Ag/AgCl | 2mm×1.8mm (exposed area only) | Sputtering, Ni layer added, Photolithography, Chemical chloridizing | None (quasi-RE) | 50mM Tris buffer (pH 7.4) with 3.5M KCl | 0mV vs. commercial Ag/AgCl | <1mV in 2h | 2004 | [92] |
| Graphite/AgCl | N/A (macroscopic) | None (macroscopic PVC encasing used) | None (quasi-RE) | KCl 0.1M | 40.8mV vs. commercial AgCl in saturated KCl | <0.2mV in 1h | 2005 | [53] |
| Hydrogen | 4mm×7mm | Evaporation, Lift-off, Galvanic platenization of Pt | None. One variant uses pHEMA membrane | KCl 1M | −850mV vs. fabricated pseudo-Ag/AgCl (after 120–1100 s of initialization drifts) | <1.5mV/h | 2000 | [85] |
| Ag/AgI | 1mm diameter | Sputtering, Lift-off, PECVD, RIE, Electrodeposition | None (quasi-RE) | PBS, pH 7.0 | −94mV vs. SCE | <1mV in 20h | 2005 | [73] |
| IrOx | 0.1mm×1mm | Photolithography, Sputtering, CVD, Electrodeposition | None (quasi-RE) | PBS | 195mV vs. Ag/AgCl | <20mV in 9 days, after initial 120 mV/day drift. 4mV std. dev. | 2003 | [30] |
| IrOx | 1500μm2 | Sputtering, Anodic growth (Electrochemical deposition) | None (quasi-RE) | 0.1M PBS | 40mV vs. Ag/AgCl | <100mV in 15 days | 2005 | [29] |