Self-calibrating ratiometric fluorescence detection of formaldehyde based on an L-histidine-functionalized lanthanide metal–organic gel

Formaldehyde (FA), the simplest and widely-applied aldehyde, can pose serious health issues when present at elevated concentrations. Herein, this study proposes a self-calibrating ratiometric sensing strategy for the sensitive detection of FA, which is based on the dual-functional ligands and multi-metal synergistic effects of L-Histidine (L-His)-functionalized Lanthanide metal-organic gels (MOGs). In this strategy, L-His and 1,3,5-benzenetricarboxylic acid (BTC) served as functional ligands coordinating with Zr 4+ , Eu 3+ , and Tb 3+ metal centers, forming three MOGs with superior photoluminescence properties: ZrEuTb-His-MOG, ZrEu-His-MOG, and ZrTb-His-MOG. Notably, ZrEuTb-His-MOG exhibits a prominent multi-metal synergistic effect: a stable self-calibration signal is generated through Zr 4+ -(L-His) ligand-to-metal charge transfer (LMCT), while the antenna effect of BTC to Tb 3+ facilitates a FA-responsive specific fluorescent signal. The synergistic interaction between these two mechanisms establishes a highly reliable self-calibrating detection system. This sensor achieves high sensitivity with a detection limit of 8.4 nM, a broad linear range of 0.001 μM–60 μM, and excellent selectivity against common interfering species. Moreover, ZrEuTb-His-MOG exhibits outstanding regenerability and long-term signal stability, qualifying it as an efficient and recyclable fluorescent probe for FA detection. Additionally, we developed a portable fluorescent test strip based on ZrEuTb-His-MOG, enabling “on-off” visual detection of both aqueous and gaseous FA with a fast response. This work provides a novel and reliable strategy for on-site FA monitoring in environmental monitoring, food safety, and public health protection.