NH2-MIL-125(Ti) and its emeraldine functionalized derivative as a chemical sensor for effective detection of dopamine

This work proposed and demonstrated Emeraldine (a Polyaniline) linking with NH2 functionalized MIL-125 (Ti) Metal Organic Framework (MOF) to be used as a chemical sensor for detection of Dopamine (DA). The covalent coupling of Emeraldine (E) with NH2-MIL-125(Ti) showed marked improvements in electron conductivity as reflected in various intrinsic parameters such as fluorescence intensities, quantum yield and dielectric functions. The fluorescence intensities changed in the following progression: NH2-MIL-125(Ti) > 1 mM PA-MIL 125(Ti) > 10 mM PA-MIL 125(Ti) > MIL-125(Ti) > E. The quantum yield in water decreased in the following progression: NH2-MIL-125(Ti) (84%) > 1 mM PA-MIL 125(Ti) (3.17%) > 10 mM PA-MIL 125(Ti) (0.348%). The oscillatory behaviour in dielectric functions, indicating electron delocalization was observed in the following progression: E > 10 mM PA-MIL 125(Ti) > 1 mM PA-MIL 125(Ti) > NH2-MIL-125(Ti). DA detection studies were successfully carried out in neutral buffer medium with excellent sensitivity. The corresponding LOD was estimated to be 10 nM and 5 nM in case of NH2-MIL-125 and PA-MIL 125 (Ti) respectively. Selectivity studies showed the influence of interferences were in the following progression: in case of NH2-MIL-125(Ti); Phenylalanine (13.72%) = Tryptophan (13.72%) > Aspartic acid (10.46%)>Glutamic acid (8.83%) > Urea (8.83%) > Glucose (8.02%) whereas with Emeraldine linking the values were; Urea (50.62%) > Glucose (44.44%) > Glutamic acid (45.62%) > Phenylalanine (45.54%) > Aspartic acid (43.95) > Tryptophan (35.40%). O-2 oxidizes (in the presence of NH2-MIL-125 and its Emeraldine linked pair), DA to dopamine-o-quinone (with an absorbance at 420 nm), forming a FRET pair. The present study showed Emeraldine linking to NH2-MIL-125(Ti), yielded lower LOD value (5 nM at Signal-to-Noise (S/N) = 3.0).