Design of a calix[4]arene-functionalized metal-organic framework probe for highly sensitive and selective monitor of hippuric acid for indexing toluene exposure.

In the present work, a novel metal-organic framework (MOF) fluorescent probe was prepared by post-synthetic modification of MIL-53-NH(Al) with carboxylatocalix[4]arene (CC[4]A). The introduced CC[4]A could not only enhance the fluorescence performance and the recognition ability of the probe, but also sustain the high stability under UV light and moisture conditions. A method based on the as-synthesized CC[4]A@MIL-53-NH(Al) probe was established for sensing hippuric acid. The detection limit was determined to be as low as 3.7 μg mL. Over the concentration range of 0.005-3 mg mL, the calibration curve was obtained with a satisfactory linearity (R = 0.993). The method was successfully used for rapid and highly selective direct monitor of hippuric acid in human urine. The sensor had great potential to be used as a simple diagnostic tool for hippuric acid in human urine which is regarded as a biological index of toluene exposure.