Detection of dyestuffs with an impedimetric sensor based on Cu2+-methyl-naphthyl cyclen complex functionalized gold electrodes

This work explored the elaboration of dyestuffs chemical sensors based on methyl-naphthyl cyclen (1,4,7,10-tetraazacyclododecane) (MNCyclen) thin films, deposited on gold electrodes and characterized by electrochemical impedance spectroscopy (EIS). The methyl-naphthyl cyclen was synthesized in three steps: first, the cyclen was protected by the formation of its glyoxal bisaminal derivative, then the glyoxal aminal of cyclen was mono-alkylated, and finally the amine groups were deprotected by removal of the aminal bridges, and the product was characterized by liquid H-1 and C-13 NMR spectroscopy. Thin films of MNCyclen were deposited on gold wafers using the spin-coating technique and characterized by means of infrared spectroscopy in ATR mode, contact angle measurements and atomic force microscopy. The chemical sensor was studied in the presence of Acid Yellow 25 (AY25), Acid Violet 7 (AV7), Indigo Blue (IB) and Acid red 1 (AR1) dyestuffs. Nyquist plots were fitted with an equivalent electrical circuit including two RC circuits in series corresponding to the MNCyclen film and its interface with the electrolyte. The main parameter that varies with dyestuff concentration is the resistance of the film/electrolyte interface (R-P). The highest sensitivity was obtained for AY25 dyestuff with a detection limit of 10(-12)M, based on an equivalent electrical model.