Adsorption kinetics of phosphonic acids and proteins on functionalized Indium tin oxide surfaces using electrochemical impedance spectroscopy

Abstract

Phosphonic acids (PAs) are known to have a spontaneous affinity for chemisorption onto several metal oxide surfaces. The self – assembled monolayer (SAM) of phosphonates provides a platform for further surface modifications using biomolecules that can be adopted for the development of sensors and biosensors. With this in view, we studied adsorption kinetics of different phosphonic acids of short chain lengths such as phosphonopropionic acid (PPA), aminobenzylphosphonic acid (ABPA), benzylphosphonic acid (BPA), butylphosphonic acid (BuPA), and a long chain decylphosphonic acid (DecPA) on ITO surface using electrochemical impedance spectroscopy (EIS) at short and long time scales. The dependence of solution concentration on formation kinetics is studied and the existences of two discrete kinetics were revealed. We show from our studies that the rate of adsorption is controlled by diffusion at small time scales. Further, the phosphonic acid modified surface is also used as a substrate for the adsorption of cytochromeC (CytC) (a heme protein) and urease (an enzyme) and the kinetics of their adsorption has been studied.