Ratiometric luminescent sensors based on metal-organic frameworks (MOFs) have emerged as a powerful tool in chemical sensing due to their ability to provide self-calibrated, reliable, and interference-resistant signals. Unlike conventional “turn-off” or “turn-on” sensors that rely solely on changes in emission intensity, ratiometric systems utilize two distinct luminescent centers—typically one analyte-responsive and one stable reference—enabling quantitative detection independent of external factors such as excitation power, probe concentration, or environmental fluctuations. This approach significantly enhances signal-to-noise ratio and measurement accuracy, making it ideal for real-world applications.
One of the most effective strategies involves the integration of lanthanide ions (e.g., Eu³⁺ and Tb³⁺) with organic ligands within MOF matrices. These dual-emission systems leverage energy transfer between the components: the organic linker acts as an antenna for lanthanide excitation, while the lanthanide ion emits at characteristic wavelengths. For example, Eu³⁺@UiO-bpydc exhibits dual emission at 530 nm (ligand) and 614 nm (Eu³⁺), allowing temperature sensing via a linear intensity ratio change across 293–353 K. Similarly, Tb³⁺@Zn-MOF shows selective response to PO₄³⁻ within seconds, with the Tb³⁺ emission decreasing due to energy transfer quenching, while the ligand emission increases. When two lanthanides are co-doped—such as Eu³⁺/Tb³⁺ in ln(OH)(bpydc)—the system enables more sophisticated sensing. In this case, rising temperature promotes energy transfer from Tb³⁺ to Eu³⁺, resulting in increased red emission and decreased green emission, enabling precise thermometry over 10–60 °C.
Fluorescent dyes also play a crucial role in dual-emission MOF sensors. By combining dye molecules with MOF hosts that emit at different wavelengths, researchers construct probes where one component serves as a reference and the other responds to analytes. RhB@Zr-MOF is a prime example: it displays emissions at 550 nm (RhB) and 420 nm (MOF), allowing detection of Fe³⁺ through selective quenching of the dye signal. The ratio I₅₅₀/I₄₂₀ remains stable under varying conditions, ensuring reliable quantification. Another notable system is Rh6G@1, which combines blue emission from the ligand (373 nm) and green emission from rhodamine 6G (570 nm). This setup enables ratiometric detection of 2,4,6-trinitrophenol (TNP), with the dye-to-ligand peak height ratio serving as the analytical signal, achieving high sensitivity and visual color changes detectable by the naked eye.CD40 Antibody Formula
Quantum dots further expand the possibilities for ratiometric sensing.ADAM10 Antibody Purity & Documentation CdTe QDs@NH₂-MIL-53(Al) emits at 528 nm (green), while the MOF emits at 425 nm (blue). Upon addition of 6-mercaptopurine, internal filtering quenches the MOF signal, while the QD fluorescence is enhanced due to surface passivation. The resulting ratio I₅₂₈/I₄₂₅ provides a robust readout unaffected by instrument drift. Similarly, BPEI-CQDs/ZIF-8 uses blue-emitting CQDs and ZIF-8’s weak emission to create a Cu²⁺ sensor: Cu²⁺ binds to amine groups on the CQDs, quenching their fluorescence, while the MOF signal remains constant, allowing accurate ratio-based quantification.
Carbon quantum dots (CQDs) offer unique advantages in ratiometric design. Their tunable emission and low toxicity make them ideal for biological and environmental applications.PMID:35196495 C-QDs@UiO-66-(COOH)₂ functions as a temperature sensor, where emission shifts from red (in organic solvents) to blue (in water) due to release of CQDs from the MOF matrix. The ratio I₄₇₀/I₆₁₀ correlates linearly with water content. Likewise, Tb³⁺@p-CDs/MOF exploits the differential response of red-emitting p-CDs and green-emitting Tb³⁺ to water, producing a visible color change in ethanol that can be used for humidity monitoring.
Perovskite quantum dots also contribute to advanced ratiometric systems. CsPbBr₃@ZJU-28 emits green light (518 nm), while ZJU-28 emits blue (442 nm). The ratio I₅₁₈/I₄₄₂ varies linearly with temperature (20–160 °C), offering a highly stable and sensitive thermometer. In contrast, CH₃NH₃PbBr₃@MOF-5 shows reversible fluorescence quenching with increasing temperature, useful for thermal imaging in harsh environments.
Luminescent complexes such as Ru(bpy)₃²⁺ and Ir(ppy)₂(bpy)⁺ are increasingly used in dual-emission MOF platforms. Ru(bpy)₃²⁺@MIL-101(Al)-NH₂ emits red light, while the MOF emits blue. Water vapor increases the blue emission intensity while stabilizing the red signal, enabling ratiometric water detection in organic solvents. MnO₂ nanosheet-coated Ru(bpy)₃²⁺-UiO-66 detects glutathione: MnO₂ oxidizes GSH to Mn²⁺, releasing the complex and restoring fluorescence. The ratio I₅₆₀/I₄₅₀ allows real-time tracking of intracellular GSH levels.
These examples highlight the versatility and robustness of dual-emission MOF sensors. They enable not only detection of ions and small molecules but also monitoring of temperature, humidity, explosives, and biomarkers. Future developments will focus on designing multifunctional, multi-analyte responsive systems using machine learning-assisted data analysis, improving biocompatibility, and enabling wearable or implantable sensing devices. With continued innovation, ratiometric MOF-based sensors are set to become indispensable tools in next-generation diagnostics, environmental monitoring, and smart materials.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com