Applications Of Metal-organic Frameworks MIL-88(Fe) In The Assay Of Dopamine

Dopamine（DA）, as an important catecholamine neurotransmitter in the central nervous system, is closely associated with locomotion and cognitive functions, as well as the endocrine regulation; deficits in brain dopamine cause Parkinson’s disease in humans. Moreover, dopamine as an adrenergic drug also plays an important role in the treatment of diseases. Therefore, the development of rapid, sensitive and accurate methods for the assay of DA is significant. Metal-organic frameworks（MOFs）, as a new type of porous hybrid materials, have many excellent chemical and physical properties owing to the diversity of center metal ions, ligands and synthetic methods. MOFs have generated many practical applications including catalysis, sensing and so on. In this paper, two kinds of iron involved metal-organic frameworks via a reported hydrothermal strategy have been utilized in the spectroanalysis of dopamine by using their catalytic and fluorescent properties. The detailed results are summarized as follows:Fe-MIL-88NH₂ as a novel peroxidase mimic and used for colorimetric detection of dopamine Uniform Fe-MIL-88NH₂ Nanoparticles with intrinsic peroxidase- like activity has been prepared according to literature, and used for colorimetric detection of dopamine. Fe-MIL-88NH₂ was employed to quickly catalyze the oxidation of the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine（TMB） to generate a blue colored oxidized TMB（oxTMB） by decomposing H₂O₂ to produce ·OH radicals. However, DA induced an inhibitory effect on the oxidation by competitive ly consuming ·OH, thus resulting in the shallow color. Therefore, the content of DA could be calculated according to colorimetric s, and the he linear range is from 50 nM to 30μM. Furthermore, the proposed method has been successfully employed for selective detection of DA in human urine with satisfactory results through the standard addition method.Fe-MIL-88NH₂ as a fluorescent sensor and used for fluorometric detection of dopamine Fe-MIL-88NH₂ has strong fluorescence attributable to the organic ligand2-aminoterephthalic acid. DA can be easily oxidized by ambient O₂ in alkaline solution（pH 8.0） to form quinones which is the good electron acceptor. Thus, Fe-MIL-88NH₂ would exhibit a dramatic fluorescent quenching resulting from the effective electron transfer from the Fe-MIL-88NH₂ to the oxidized dopamine-quinone. Herein, a simple fluorescence method for DA detection with excellent selectivity was developed, and the linear response range was from 1 μM to 0.1 mM and 0.3 mM to 6 mM with detection limit 0.83 nm. Moreover, the proposed method has been applied to detect DA in dopamine hydrochloride injection and human blood serum with satisfactory results.Assay for dopamine based on the turn-on fluorescence of Fe-MIL-88 metal-organic frame works–hydrogen peroxide–o-phenylenediamine system Fe-MIL-88 with intrinsic peroxidase- like catalytic activity tended to oxidize the nonfluorescent OPD into the fluorescent 2,3-diaminophenazine（DAP） with the presence of H₂O₂ to exhibit a weak fluorescence. When DA was introduced, the autoxidation of DA to yield hydroxyl radical（·OH） was further enhanced by Fe³⁺site in Fe3-μ3-oxo clusters exiting in Fe-MIL-88 MOFs, meanwhile the generated Fe²⁺appeared to involve a Fenton type reaction in the present of H₂O₂ to cause a continuous production of ·OH radicals which greatly enhanced the conversion efficiency of the OPD to fluorescent DAP. Thus, the turn-on fluorescence method for the DA detection was established, which the linear range was from 50 nm to 30 μM with detection limit 46 nm. Furthermore, the proposed method has been reliably applied to determine dopamine content in dopamine hydrochloride injection and human urine with satisfactory results.