Table 1.
Comparison of hydrogel based pH sensors .* estimated by characteristic curves
| Sensor type | Data channel | Transducer resolution | Sensitivity per pH unit | Accuracy of measurement | pH working range | Hydrogel | Minimal response time | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|
|
| |||||||||||
| overall | best point | ||||||||||
|
|
|
||||||||||
| Transducer signal | pH unit | Transducer signal | pH unit | Material | Thickness | ||||||
| Refractometric sensor [46] | refractive index | 2.5x10−4 10−5/4x10−2 | 3.11x10−2 | ± 3.75x10- * | ± 1.64x10-3 * | ± 1.1x10-4 | ± 4.8x10-4 | 7-7.75 | HEMA-DMAEMA | 300 nm (dry) | ∼ 80 s |
| Holographic sensor [58] | wavelength | 6x10−3 (1nm/165nm) | 165 nm | ± 5.3 nm * | ± 0.032 * | ± 3.1 nm * | ± 0.019 * | 5 - 7 | PHEMA-co-MAA | 10 μm | ∼ 250 s |
| CCA sensor[55] (Braggdiffraction) | wavelength | 3,3x10−3 (1nm/300nm) | 74.2 nm | - | - | - | - | 4.3-8.5 | PAAm-PCCA | 125 μm | 10 min |
| Conductimetric sensor [63] | resistance | - | 100 Ω | - | - | ± 5.2Ω | ± 0.052 | 7 - 8 | HEMA-DMAEMA | 8 μm | 350 s |
| Quartz crystalmicro balance[64] | frequency damping | 3.3x10−6 (0.1Hz/30kHz) | 13.2 kHz 25.467 kHz | ± 0.62 kHz ± 1.085 kHz | ± 0.047 ± 0.042 | ± 179 Hz ± 89.5 Hz | ± 0.013 ± 3.5x10-3 | 2.55 – 3.45 | PVA-PAA | 390 nm (dry) | 500 ms |
| Magnetoelastic sensor [67] | frequency | 2,4x10−4 0.4Hz/1.7kHz | 506 Hz | ± 66 Hz | ± 0.13 | - | - | 4,4 – 8,5 | poly(AA-co-IOA) | 1.4 μm | 120 s |
| Microcantilever [74] | deflexion | 5x105 (1nm/20μm) | 20.3 μm | ± 1.15 μm * | ± 0.057 * | ± 0.3 μm * | ± 0.015 * | 6 - 6,8 | PMAA-PEGDMA | 2.2 μm | few minutes |
| Microcantilever [75] | deflexion | 2,9x105 (1nm/35μm) | 1000 nm | ± 5 % | ± 0.05 | - | - | 6 - 9 | AAm-DMAEMA | 15 μm | 15 min |
| Bending plate sensor [79] | resistance | 1,67x10-5 (1μV/60mV) | 14.55 mV * | ± 3.5 mV * | ± 0.24 * | ± 1.9 mV * | ± 0.13 * | 5.5 - 11 | PVA-PAA | 40 μm | ∼ 12 min |
HEMA:DMAEMA: 2-hydroxyethyl methacrylate - N,N-dimethylaminoethyl methacrylate
PHEMA-co-MAA: poly(hydroxyethyl methacrylate-co- methacrylic acid) different acidic and basic monomers where also used
PAAm-PCCA: poly(acrylamide) - polymerised crystalline colloidal array
PVA-PAA: poly(vinyl alcohol) – poly(acrylic acid)
poly(AA-co-IOA): poly(acrylic acid-co-isooctyl acrylate)
PMAA-PEGDMA: poly (methacrylic acid)-Poly(ethylene glycol) dimethacrylate
AAm-DMAEMA: acrylamide - N,N-dimethylaminoethyl methacrylate