Rational design of a functionalized aluminum metal-organic framework as a turn-off fluorescence sensor for α-ketoglutaric acid

A 3D metal-organic framework (MOF) called Al-DUT-5-N2H3 (1) (DUT: Dresden University of Technology) was prepared hydrothermally using Al(III) salt and a hydrazinyl functionalized linker called 2-hydrazinyl-[1,1'-biphenyl]-4,4'-dicarboxylic acid (BPDC-N2H3). Material 1 was successfully characterized by X-ray powder diffraction (XRPD), FT-IR spectroscopy, N-2 sorption (BET) experiment, thermogravimetric analysis (TGA), EDX and FE-SEM analyses. The activated form of material 1 (called 1') was achieved by a direct heating process. Material 1' was successfully employed for the solution-phase fluorescence detection of alpha-ketoglutaric acid (alpha-KG). It showed high detection performance even when there were other competitive analytes present in the mixture. Material 1' is the first MOF-based fluorescent turn-off sensor for the detection of alpha-KG. The response time for alpha-KG is exceptionally low (60 s) as compared to any other reported alpha-KG sensor. The limit of detection (LOD) was found to be 0.61 mu M, which is far better as compared to any other reported sensor for alpha-KG to date. The mechanism for alpha-KG sensing was thoroughly investigated and proposed to be PET (photoinduced electron transfer) process by TD-DFT (time-dependent DFT) calculations.