Development of a label-free electrochemical aptasensor based on diazonium electrodeposition: Application to cadmium detection in water.

In this study we have developed a new aptasensor for cadmium (Cd ²⁺ ) detection in water. Gold electrode surface has been chemically modified by electrochemical reduction of diazonium salt (CMA) with carboxylic acid outward from the surface. This was used for amino-modified cadmium aptamer immobilization through carbodiimide reaction. Chemical surface modification was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). This latter was also used for Cd ²⁺ detection. The aptasensor has exhibited a good linear relationship between the logarithm of the Cd ²⁺ concentration and the impedance changes in the range from 10 ^-3 to 10 ^-9  M with a correlation R ² of 0.9954. A high sensitivity was obtained with a low limit of detection (LOD) of 2.75*10 ^-10  M. Moreover, the developed aptasensor showed a high selectivity towards Cd ²⁺ when compared to other interferences such as Hg ²⁺ , Pb ²⁺ and Zn ²⁺ . The developed aptasensor presents a simple and sensitive approach for Cd ²⁺ detection in aqueous solutions with application for trace Cd ²⁺ detection in spring water samples.
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