Eu3+-Doped aluminum Metal-Organic Frameworks: A versatile platform for ratiometric detection of histidine and Water, and visible fingerprint identification

Ratiometric fluorescent sensors possess inherent self-calibration features that enable the mitigation of interference from factors unrelated to the analysis. This characteristic results in heightened sensitivity and more pronounced visual detection during qualitative and quantitative analytical processes. A ratiometric fluorescence probe Eu/Al-MOF has been successfully prepared via Eu3+ doped aluminum metal - organic frameworks. Upon introducing histidine, the fluorescence intensity of Eu3+ showed a noteworthy increase, whereas the intensity originating from the ligand decreased owing to enhancing energy transfer from the ligand to Eu3+ ions in the probe. Eu/Al-MOF could detect histidine over a wider linear range of 0.1-400 mu M and a lower detection limit of 0.04 mu M. Besides, in the presence of water in organic solvents, the excited state of Eu3+ in the probe could be coupled with the O-H oscillation of water molecules, and the excited state energy from Eu3+ would be transferred to the water molecules so that only the fluorescence intensity of Eu3+ gradually decreased. Thus, the proportional detection of trace water could be realized. In ethanol and DMF, the detection range for water was 0.1-20 % and 0.5-20 %, respectively. Moreover, it was found that Eu/Al-MOF could efficiently achieve the visualization identification of fingerprints, providing the possibilities for applying the nano-sensor as a promising multifunctional fluorescence probe.