title: A miniaturised electrochemical affinity assay based on a wall-free sample droplet and micro-dispensing of the redox-labelled binding partner.
abstract: An affinity-assay was developed that is based on the modulation of the diffusion coefficient of a redox-labelled hapten upon complementary recognition of the analyte leading to an increase of molecular weight and hence to a decrease of the diffusion coefficient. The slower diffusion is monitored by means of cyclic voltammetry. In order to demonstrate the feasibility of this assay format, recognition of biotin by streptavidin has been chosen as a model system. Labelling of biotin was achieved by covalent binding of a ferrocene derivative to the biotin unit. To reduce the consumption of expensive compounds and to allow automatisation of the assay a novel miniaturised set-up was developed based on a wall-free sample droplet which forms the electrochemical cell with typical volumes of up to 10 microl. This droplet is dispensed by means of a step-motor driven syringe pump through a specially designed electrode holder spanning the gap between a micro-working electrode and a macroscopic counter electrode. By means of a piezo-driven micro-dispenser a predefined number of nano-droplets (100 pl volume each) containing the redox-labelled hapten are shot into the sample droplet. By this, any physical contact and hence any cross-contamination between the sample and the reagent solution could be avoided. Signal amplification can be achieved by redox recycling between the micro-electrode and the perpendicular positioned macroscopic counter electrode.
authors.affiliation: Ruhr-Universität Bochum, Analytische Chemie-Elektroanalytik & Sensorik, Universitätsstr. 150, D-44780 Bochum, Germany. mosbach@anachem.ruhr-uni-bochum.de
authors.forename: M
authors.initials: M
authors.lastname: Mosbach
authors.forename: T
authors.initials: T
authors.lastname: Laurell
authors.forename: J
authors.initials: J
authors.lastname: Nilsson
authors.forename: E
authors.initials: E
authors.lastname: Csöregi
authors.forename: W
authors.initials: W
authors.lastname: Schuhmann
mesh_terms: D015374:Biosensing Techniques / Q000295:instrumentation*; D001710:Biotin; D004563:Electrochemistry; D004867:Equipment Design; D006241:Haptens; D007118:Immunoassay / Q000295:instrumentation / Q000379:methods; D008904:Miniaturization; D010084:Oxidation-Reduction; D019809:Streptavidin
chemical_list: D006241:Haptens; D001710:Biotin; D019809:Streptavidin