Table 1.
Photophysical properties of some typical pH indicators and the sensors reported herein.
| Sensors a) | Types of fluorophores | λmax, abs (nm) | λmax, em (nm) | Stokes Shift (nm) b) | pKa | Fmax/Fminc) | Specificity | ref |
|---|---|---|---|---|---|---|---|---|
| Fluorescein | Fluorescein | 472 (pH 5.0) 490 (pH 9.0) |
515 (pH 5.0) 515 (pH 9.0) |
43 (pH 5.0) 25 (pH 9.0) |
6.4 | ~10 | Cell impermeable | 49 |
| Oregon Green 488 Carboxylic acid | Fluorescein | 472 (pH 3.0) 490 (pH 8.1) |
513 (pH 3.0) 515 (pH 9.0) |
41 (pH 3.0) 25 (pH 9.0) |
4.7 | ~8 | Cell impermeable | 49 |
| Intracellular pH sensors | ||||||||
| Carboxylic SNARF-1 | Seminaphtharh odafluor | 515 (pH 6.0) 575 (pH 9.0) |
590 (pH 6.0) 650 (pH 9.0) |
75 (pH 6.0) 75 (pH 9.0) |
7.5 | ~8 | Physiological pH | 49, 50 |
| LysoTracker Red DND 99 | Dipyrromethen e-boron difluoride | 577 (pH 4.0) 577 (pH 8.0) |
590 (pH 4.0) 590 (pH 8.0) |
13 (pH 4.0) 13 (pH 8.0) |
NA | ~1 | Lysosomes | 35, 49, 51 |
| LysoTracker Green DND 26 | Dipyrromethen e-boron difluoride | 504 (pH 4.0) 504 (pH 8.0) |
511 (pH 4.0) 511 (pH 8.0) |
7 (pH 4.0) 7 (pH 8.0) |
NA | ~1 | Lysosomes | 35, 49, 51 |
| LysoSensor Blue DND 167 | Anthracene | 373 (pH 3.1) 373 (pH 6.1) |
425 (pH 3.1) 425 (pH 6.1) |
52 (pH 3.1) 52 (pH 6.1) |
5.1 | ~6 | Lysosomes | 35, 49, 51 |
| LysoSensor Green DND 153 | Benzimidazo-[2, 1, a]-benz-[d,e]-isoquinolin-7-one | 442 (pH 4.1) 442 (pH 8.9) |
505 (pH 4.1) 505 (pH 8.9) |
63 (pH 4.1) 63 (pH 8.9) |
7.5 | ~5 | Lysosomes | 35, 49, 51 |
| LysoSensor Green DND 189 | Benzimidazo-[2, 1, a]-benz-[d,e]-isoquinolin-7-one | 452 (pH 2.9) 442 (pH 7.1) |
505 (pH 2.9) 505 (pH 7.1) |
53 (pH 2.9) 63 (pH 7.1) |
5.2 | ~7 | Lysosomes | 35, 49, 51 |
| 4 | Naphthalimide | 387 (pH 3.0) 402 (pH 9.0) |
527 (pH 3.0) 527 (pH 9.0) |
140 (pH 3.0) 125 (pH 9.0) |
6.8 | 182 | Lysosomes | This work |
| SM1 | Naphthalimide | 387 (pH 3.0) 402 (pH 9.0) |
527 (pH 3.0) 527 (pH 9.0) |
140 (pH 3.0) 125 (pH 9.0) |
6.0 | 180 | Lysosomes | This work |
| SM2 | Naphthalimide | 387 (pH 3.0) 402 (pH 9.0) |
527 (pH 3.0) 527 (pH 9.0) |
140 (pH 3.0) 125 (pH 9.0) |
5.9 | 64 | Lysosomes | This work |
| SM3 | Naphthalimide | 387 (pH 3.0) 402 (pH 9.0) |
527 (pH 3.0) 527 (pH 9.0) |
140 (pH 3.0) 125 (pH 9.0) |
6.8 | 100 | Lysosomes | This work |
| Extracellular pH sensors | ||||||||
| CHFOE | Fluorescein | 470 (pH 5.0) 526 (pH 10.0) |
523 (pH 5.0) 545 (pH 10.0) |
53 (pH 5.0) 19 (pH 10.0) |
7.1 | ~10 | 7 | |
| DHFA | Fluorescein | 470 (pH 5.0) 516 (pH 10.0) |
516 (pH 5.0) 540 (pH 10.0) |
46 (pH 5.0) 24 (pH 10.0) |
8.4 | ~10 | 7 | |
| AMPN | Naphthalimide | 400 (pH 3.0) 432 (pH 9.0) |
517 (pH 3.0) 517 (pH 9.0) |
117 (pH 3.0) 85 (pH 9.0) |
7.5 | ~5 | 8 | |
| P1 | Naphthalimide | 388 (pH 3.0) 412 (pH 9.0) |
512 (pH 3.0) 521 (pH 9.0) |
114 (pH 3.0) 109 (pH 9.0) |
5.2 | 11 | This work | |
| P2 | Naphthalimide | 388 (pH 3.0) 412 (pH 9.0) |
512 (pH 3.0) 521 (pH 9.0) |
114 (pH 3.0) 109 (pH 9.0) |
5.2 | 5.5 | This work | |
| P3 | Naphthalimide | 388 (pH 3.0) 412 (pH 9.0) |
512 (pH 3.0) 521 (pH 9.0) |
114 (pH 3.0) 109 (pH 9.0) |
7.0 | 13.5 | This work | |
a)
Chemical structures of the sensors reported by other scientists were given in supplementary data (S-Figure 1).
b)
Stokes shift is the difference of the emission maximum (λmax, em) and absorption maximum (λmax, abs), e.g. λmax, em − λmax, abs.
c)
The ratios of the maximum fluorescence intensity (Fmax) divided by the minimum fluorescence intensity (Fmin) indicate the sensors’ sensitivities.