Table 2.
Comparison of sensor responses of 433.92 MHz SAW coated with SWCNTs and MWCNTs dispersed separately in ethanol and toluene. Adapted with permission from [97], copyright (2005) Elsevier.
| Type of VOC | SWCNTs Dispersed into Ethanol | MWCNTs Dispersed into Ethanol | ||||||
| Sensitivity (∆f/f)/c (ppm/ppm) | Sensitivity ∆f/c (kHz/ppm) | LOD (ppm) | Absolute Sensitivity ∆f/c/∆fw (Hz/ppm/kHz) | Sensitivity (∆f/f)/c (ppm/ppm) | Sensitivity ∆f/c (kHz/ppm) | LOD (ppm) | Absolute Sensitivity ∆f/c/∆fw (Hz/ppm/kHz) | |
| Ethanol | 15.88 | 6.89 | 1.3 | 34.45 | 4.13 | 1.79 | 5.0 | 8.95 |
| Ethyl Acetate | 7.67 | 3.32 | 2.7 | 16.6 | 2.09 | 0.90 | 10.0 | 4.50 |
| Toluene | 7.32 | 3.17 | 2.8 | 15.85 | 2.33 | 1.01 | 9.0 | 5.05 |
| SWCNTs Dispersed into Toluene | MWCNTs Dispersed into Toluene | |||||||
| Sensitivity (∆f/f)/c (ppm/ppm) | Sensitivity ∆f/c (kHz/ppm) | LOD (ppm) | Absolute Sensitivity ∆f/c/∆fw (Hz/ppm/kHz) | Sensitivity (∆f/f)/c (ppm/ppm) | Sensitivity ∆f/c (kHz/ppm) | LOD (ppm) | Absolute Sensitivity ∆f/c/∆fw (Hz/ppm/kHz) | |
| Ethanol | 14.62 | 6.34 | 1.4 | 31.70 | 2.02 | 0.87 | 10.2 | 4.35 |
| Ethyl Acetate | 12.58 | 5.45 | 1.6 | 27.25 | 3.99 | 1.73 | 5.2 | 8.65 |
| Toluene | 17.22 | 7.47 | 1.2 | 37.35 | 4.67 | 2.02 | 4.4 | 10.10 |
Measurements were conducted at room temperature 20°C, relative humidity 15%, exposure time of 10 min, noise level 3 kHz at S/N of 3. (∆f/f) represent fractional frequency shift, ∆f frequency shift, c concentration of vapors, (∆fw) frequency shift due to coating of CNTs.