Modulation of the diffusion coefficient of a hapten-modified redox speciesas a basis for an amplified electrochemical affinity assay

An affinity assay was developed that is based on the modulation of the diff usion coefficient of an electroactive label upon complementary recognition leading to an increase of the molecular weight. Using an electroanalytical technique, which is correlated to the diffusion coefficient of the redox sp ecies, e.g., cyclic voltammetry, the decrease of the diffusion coefficient can be monitored as a decrease of the diffusion-limited current. Signal amp lification was achieved by redox recycling using a microelectrode that is p ositioned in close distance to a conducting surface. The amplification rate can be adapted by varying the distance between the microelectrode and the conducting surface. As a model system for molecular recognition, the biotin -streptavidin system has been chosen using a ferrocene-labeled biotin deriv ative as electroactive species. The generality of the approach was proved b y extension of the basic assay to related sandwich assays and by miniaturiz ation using a wall-free droplet cell. (C) 2000 Elsevier Science B.V. All ri ghts reserved.