Microfluidic devices with integrated dual-capacitively coupled contactless conductivity detection to monitor binding events in real time

This paper describes the fabrication of microfluidic devices with integrated dual capacitively coupled contactless conductivity detection (C4D) for monitoring binding events. The avidin-biotin model was employed to show the feasibility of the C4D as a detection mode. The binding event was monitored using microfluidic channels fabricated in poly(dimethylsiloxane) (PDMS). Detection electrodes were fabricated in a three-electrode arrangement by sputtering a Ti/Au/Ti layer over a glass wafer, which were electrically insulated by a SiO2 layer. The dielectric layer over the sensing electrode area was chemically modified with biotin. After introducing avidin solutions on microchannels, binding events were detected on conductivity sensorgrams by applying a 300-kHz-sinusoidal waveform with amplitude of 2 V (peak-to-peak) to the exciting electrode. The electrical characterization of the modified electrode indicates that the conductivity signal is changed due to the alteration on the dielectric constant of the surface. The limit of detection for avidin was 1.5 μg mL−1, representing 23 nmol L−1.