Construction and characterisation of a modular microfluidic system: coupling magnetic capture and electrochemical detection

This work presents the fabrication and characterisation of a versatile lab-on-a-chip system that combines magnetic capture and electrochemical detection. The system comprises a silicon chip featuring a series of microband electrodes, a PDMS gasket that incorporates the microfluidic channels, and a polycarbonate base where permanent magnets are hosted; these parts are designed to fit so that wire bonding and encapsulation are avoided. This system can perform bioassays over the surface of magnetic beads and uses only 50 mu L of bead suspension per assay. Following detection, captured beads are released simply by sliding a thin iron plate between the magnets and the chip. Particles are captured upstream from the detector and we demonstrate how to take further advantage of the system fluidics to determine enzyme activities or concentrations, as flow velocity can be adjusted to the rate of the reactions under study. We used magnetic particles containing beta-galactosidase and monitored the enzyme activity amperometrically by the oxidation of 4-aminophenol, enzymatically produced from 4-aminophenyl-beta-d-galactopyranoside. The system is able to detect the presence of enzyme down to approximately 50 ng mL(-1).