Detection of Gadolinium with an Impedimetric Platform Based on Gold Electrodes Functionalized by 2-Methylpyridine-Substituted Cyclam

Gadolinium is extensively used in pharmaceuticals and is very toxic, so its sensitive detection is mandatory. This work presents the elaboration of a gadolinium chemical sensor based on 2-methylpyridine-substituted cyclam thin films, deposited on gold electrodes, using electrochemical impedance spectroscopy (EIS). The 2-methylpyridine-substituted cyclam (bis-N-MPyC) was synthesized in three steps, including the protection of cyclam by the formation of its CH2-bridged aminal derivative; the product was characterized by liquid 1H and 13C NMR spectroscopy. Spin-coated thin films of bis-N-MPyC on gold wafers were characterized by means of infrared spectroscopy in ATR (Attenuated Total Reflectance) mode, contact angle measurements and atomic force microscopy. The impedimetric chemical sensor was studied in the presence of increasing concentrations of lanthanides (Gd3+, Eu3+, Tb3+, Dy3+). Nyquist plots were fitted with an equivalent electrical circuit including two RC circuits in series corresponding to the bis-N-MPyC film and its interface with the electrolyte. The main parameter that varies with gadolinium concentration is the resistance of the film/electrolyte interface (Rp), correlated to the rate of exchange between the proton and the lanthanide ion. Based on this parameter, the detection limit obtained is 35 pM. The bis-N-MPyC modified gold electrode was tested for the detection of gadolinium in spiked diluted negative urine control samples.

Development of an impedimetric sensor based on carbon dots and chitosan nanocomposite modified electrode for Cu (II) detection in Water

The fast and sensitive detection of copper ions would be essential for water monitoring. Herein, we report a novel development of impedimetric sensor based on carbon dots/chitosan nanocomposite. Carbon dots (CDs) were synthesized by simple heating of acidic aqueous solution of glucose. The CDs were characterized by TEM, FTIR, XRD, UV-visible, and PL. These measurements revealed that the CDs possess a mean size of 3.2 nm, graphitic structure with carboxyl and hydroxyl groups on the surface, and show particular optical properties. A glassy carbon electrode (GCE) was modified with a carbon dots/chitosan (CHITO) nanocomposite, and was characterized by transmission electron microscopy and electrochemical impedance spectroscopy (EIS). The CDs-CHITO/GCE electrode exhibits large surface area, good conductivity film, and charge transfer at interface film/electrolyte. The proposed impedimetric sensor exhibits a linear response to Cu(II) over 10-9 M to 10-5 M rang with a limit of detection at about 5×10-10 M. In addition, the sensor shows good selectivity toward Cu(II) ions, which is less than 5 %.Therefore, the as-developed impedimetric sensor exhibits good reproducibility, stability, selectivity, and a low limit of detection, which augur well for its application in water safety control processes.