Calix[4]arene functionalized gold nanoparticles: Application in colorimetric and electrochemical sensing of cobalt ion in organic and aqueous medium

Tailored calixarene derivative has been synthesized by incorporating dithiocarbamate unit, which has been anchored on the surface of the gold nanoparticles. Gold nanoparticle is a specific class of colorimetric transducer exhibiting intense red colour due to SPR absorbance. Anchoring of calixarene on to the surface of the gold nanoparticles has been confirmed by IR, UV–vis, TEM and EDX analysis. The interaction of this new material with various metal ions has been investigated and it exhibited distinct colour change from pink to blue, detectable even by naked-eyes, in presence of Co(II) ion. Binding of Co(II) is confirmed by clustering of gold nanoparticle as observed under TEM as well as DLS study. The detection limit for metal ion obtained by colorimetric method is 10−9 M. The same material has also been used for electrochemical sensing of Co(II) in aqueous media where amperometric response due to binding of metal ion has been investigated. The calixarene functionalized gold nanoparticles was immobilized in a conducting polymer (polyaniline) matrix. In this method, a detection limit of 10−12 M for Co(II) has been achieved. Competitive sensing study revealed no significant interference from other metal ions used in this study in both the sensing methods.