A Review of Fluorescent pH Probes: Ratiometric Strategies, Extreme pH Sensing, and Multifunctional Utility
Abstract
1. Introduction
- (a)
- Intramolecular Charge Transfer (ICT)
- (b)
- Photoinduced Electron Transfer (PET)
- (c)
- Fluorescent Resonance Energy Transfer (FRET)
2. Acidic Fluorescent Probes
2.1. Strongly Acidic Fluorescent Probes
2.2. Weakly Acidic Fluorescent Probes
2.3. Wide-Range Acidic Fluorescent Probes
3. Alkaline Fluorescent Probes
3.1. Strongly Alkaline Fluorescent Probes
3.2. Weakly Alkaline Fluorescent Probes
3.3. Wide-Range Alkaline Fluorescent Probes
4. Near-Neutral Fluorescent Probes
5. Wide-Range pH Fluorescent Probes
6. Summary and Outlook
7. Future Work
- (1)
- Probe enhancement strategies: Key strategies for advancing fluorescent probes include optimizing ICT efficiency through stronger electron donor/acceptor groups or nano-assemblies with signal amplification capabilities, and designing universal probes operable across broad pH ranges (e.g., pH 0–14) or specialized probes with ultra-high sensitivity at extreme values (e.g., pH > 13 or pH < 1).
- (2)
- Hysteresis characteristics of pH sensors: To enhance sensor reversibility and long-term stability, optimize sensing membrane design—including functional groups and cross-linking density—while analyzing OH− ion accumulation kinetics. Additionally, explore surface modification or buffering agents to minimize OH− retention and improve stability.
- (3)
- Stability: Structural modification of probe molecules (such as introducing large steric hindrance groups, oxidation/reduction resistant groups) or encapsulating them in stable carrier materials (such as silica and metal organic framework (MOFs)) to enhance their long-term photostability and chemical stability in specific harsh environments, such as strong acids/bases and highly reactive oxygen species.
- (4)
- Multi-functionality of sensors: In addition to pH detection, fluorescent sensors can also be used to detect other environmental parameters such as temperature, humidity, and ion concentration. In the future, sensor design based on multifunctional fluorescent materials can be explored to achieve simultaneous detection of multiple parameters and improve the application value of sensors.
- (5)
- Mechanical performance of sensors: The deployment of fiber optic sensors in mechanically demanding environments necessitates enhanced durability—a currently understudied aspect. Future work must: (a) engineer organic–inorganic hybrid coatings with gradient modulus, optimizing interfacial binding energy through MD simulations to ensure structural integrity under extreme stress; and (b) develop multi-scale mechanical models quantifying deformation-induced optical signal drift, enabling rational anti-interference design.
- (6)
- Frontier biomedical applications: Engineer a theranostic probe by merging the detection function of this sensor with photodynamic therapy (PDT) or photothermal therapy (PTT) capabilities, enabling concurrent diagnosis and treatment.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Probe | Core Fluorophore | Mechanism | Excitation Wavelength (nm) | Emission Wavelength (nm) | Ratio | pH Response Range | Applications | Ref. |
---|---|---|---|---|---|---|---|---|
1 | Camphor | ICT | 355 | 416, 486 | I486/I416 | 1.04–2.35 | Fabrication of hybrid cellulose hydrogel, and measurement of vinegar and fruit acids | [42] |
2 | Coumarin | PET | 385 | 460 | - | 3.06–0.80 | Fluorescent imaging of E. coli | [43] |
3 | Coumarin | ICT | 365 | 563 | - | 1.3–1.8 | Response to N2H4 | [44] |
4 | Imidazole [1, 2-A] indole | ICT | 350 | 450 | - | 3.2–4.4 | Fluorescent imaging of saccharomyces cerevisiae | [51] |
5 | Pyrazole, pyridine | ICT | - | 487, 585 | I585/I487 | 3.0–5.5 | Freshness assessment of pork and chicken breast, fluorescent imaging in HeLa cells and zebrafish | [52] |
6 | Rhodamine | FRET | 365 | 480, 590 | I590/I480 | 3.9–5.3 | Lysosomal pH detection in MCF-7 cells | [53] |
7 | Rhodamine B | ICT | 526 | 585 | - | 5.0–6.0 | Fluorescent imaging of TM3 cells | [54] |
8 | Fe doped carbon dots | Static quenching (SQE) | 410 | 475 | - | 2.0–7.0 | Response to NO2− | [55] |
9 | Benzindole | ICT | 436 | 418, 545 | I545/I418 | 2.1–7.4 | Freshness assessment of food samples (milk, shrimp, and scallops). Fluorescent imaging in zebrafish and onion epidermal cells | [56] |
10 | N,S-CQDs | - | 365 | 420 | - | 2.01–5.11 | Gastric fluid pH Measurement | [57] |
11 | Naphthylimide | ICT | 405 | 525 | - | 10.5–12.5 | Fabrication of PVA hydrogel for pH detection in concrete | [60,61] |
12 & 13 | Naphthylimide | ICT | 365 | 520&530 | - | 9.0–13.0 | Measurement of concrete simulated pore fluid pH | [62] |
14 | Coumarin | ICT | 365 | 459, 577 | I459/I577 | 9.0–13.0 | Environmental water samples, pH test strips | [63] |
15 | Benzo[d]imidazole | ICT | - | 607 | - | 7.0–9.30 | - | [68] |
16 | Quinoline | ICT | 488 | 630 | - | 6.50–10.00 | Mitochondrial pH detection in HeLa, HepG2, and L-O2 cells | [69] |
17 | Coumarin | PET | 400 | 476 | - | 6.50–9.98 | Fluorescent imaging in zebrafish | [70] |
18 | Naphthalimide | ICT | 380 | 479 | - | 7.4–12.0 | Fabrication of test strips for fluorescent imaging in HeLa cells, and detection in real water/food samples | [71] |
19 | Myristaldehyde | ICT | 400 | 580 | - | 7.45–12.89 | Fluorescent imaging in HeLa cells and zebrafish | [72] |
20 | Coumarin | FRET | 420 | 485, 608 | I485/I608 | 6.0–8.0 | Mitochondrial pH detection in HeLa cells | [66] |
21 & 22 | Fluorescein | ESIPT, ICT | 320 | 518 & 516 | - | 5.40–7.30 6.50–8.00 | - | [76] |
23 & 24 & 25 | Hemicyanine | ICT | 460 | 530, 560 | I530/I560 | 6.47, 6.47 & 6.40 | Fluorescent imaging in HeLa cells with H2O2 response | [77] |
26 | Benzothiazole | ICT | 600 | 672 nm, 715 nm | I672/I715 | 6.2–7.8 | pH detection in real water/human serum, freshness assessment of pork/chicken breast, fluorescent imaging in HeLa cells with viscosity response | [78] |
27 | Coumarin | PET | 545 | 650 | - | 2.00–6.65, 6.65–12.00 | Lysosomal fluorescent imaging in HeLa and SH-SY5Y cells | [79] |
28 | 8-Hydroxyquinoline | ICT | 365 | 665, 710 | I710/I665 | 5.0–13.0 | - | [80] |
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Xu, W.; Ma, Z.; Tian, Q.; Chen, Y.; Jiang, Q.; Fan, L. A Review of Fluorescent pH Probes: Ratiometric Strategies, Extreme pH Sensing, and Multifunctional Utility. Chemosensors 2025, 13, 280. https://doi.org/10.3390/chemosensors13080280
Xu W, Ma Z, Tian Q, Chen Y, Jiang Q, Fan L. A Review of Fluorescent pH Probes: Ratiometric Strategies, Extreme pH Sensing, and Multifunctional Utility. Chemosensors. 2025; 13(8):280. https://doi.org/10.3390/chemosensors13080280
Chicago/Turabian StyleXu, Weiqiao, Zhenting Ma, Qixin Tian, Yuanqing Chen, Qiumei Jiang, and Liang Fan. 2025. "A Review of Fluorescent pH Probes: Ratiometric Strategies, Extreme pH Sensing, and Multifunctional Utility" Chemosensors 13, no. 8: 280. https://doi.org/10.3390/chemosensors13080280
APA StyleXu, W., Ma, Z., Tian, Q., Chen, Y., Jiang, Q., & Fan, L. (2025). A Review of Fluorescent pH Probes: Ratiometric Strategies, Extreme pH Sensing, and Multifunctional Utility. Chemosensors, 13(8), 280. https://doi.org/10.3390/chemosensors13080280