Calix[4]arene based molecules for amino-acid detection

The ability of calixarene based molecules to form complexes with amino-acids has been the central topic of many studies. In this report we studied the potential complex formation between calix[4]arene based molecules and some amino-acids including arginine and lysine using faradic electrochemical impedance spectroscopy (EIS). Calix[4]arene–amino-acid complex formation was tested under two pH conditions. In this study we used cyclic voltammetry to determine the electrochemical properties of the different layers immobilized on gold electrode surfaces. The electrodes were initially functionalized using cysteamine and then used as a substrate for calix[4]arene immobilization. Impedance spectroscopy permits the study of the electrical properties of the different layers and also allows for the detection of amino-acids binding to calix[4]arene.Scanning electron microscopy (SEM) was utilised to study the topography and the organisation of calixarene on the electrode surface. Fourier transform infrared spectroscopy (FTIR) was used to study the molecular structure of the different layers on the electrode surface.Cyclic voltammetry and FTIR proved that calixarene was assembled at the thiol functionalized gold surface. SEM shows a crystalline organisation; a dendritic structure in the case of the calixarene modified by the carboxylic acid groups (calix 1) and the calixarene with sulphonated long chain (calix 3). The benzyl modified calixarene (calix 2) shows a cubic structure organisation. Faradic impedance spectroscopy allows the following of the amino-acid–calixarene interaction. Calix 1 presented the highest sensitivity to arginine and lysine and allowed 1 × 10−3 M of arginine and 6 × 10−3 M of lysine to be detected.